Spock 1.0 has been finally released. About new features and enhancements I already wrote two blog posts. One of the recent changes was a separation on artifacts designed for specific Groovy versions: 2.0, 2.2, 2.3 and 2.4 to minimize a chance to come across a binary incompatibility in runtime (in the past there were only versions for Groovy 1.8 and 2.0+). That was done suddenly and based on the messages on the mailing list it confused some people. After being twice asked to help properly configure two projects I decided to write a short post presenting how to configure Spock 1.0 with Groovy 2.4 in Maven and Gradle. It is also a great place to compare how much work is required to do it in those two very popular build systems. Maven Maven does not natively support other JVM languages (like Groovy or Scala). To use it in the Maven project it is required to use a third party plugin. For Groovy the best option seems to be GMavenPlus (a rewrite of no longer maintained GMaven plugin). An alternative is a plugin which allows to use Groovy-Eclipse compiler with Maven, but it is not using official groovyc and in the past there were problems with being up-to-date with the new releases/features of Groovy. Sample configuration of GMavenPlus plugin could look like: org.codehaus.gmavenplus gmavenplus-plugin 1.4 compile testCompile As we want to write tests in Spock which recommends to name files with Spec suffix (from specification) in addition it is required to tell Surefire to look for tests also in those files: maven-surefire-plugin ${surefire.version} **/*Spec.java **/*Test.java Please notice that it is needed to include **/*Spec.java not **/*Spec.groovy to make it work. Also dependencies have to be added: org.codehaus.groovy groovy-all 2.4.1 org.spockframework spock-core 1.0-groovy-2.4 test It is very important to take a proper version of Spock. For Groovy 2.4 version 1.0-groovy-2.4 is required. For Groovy 2.3 version 1.0-groovy-2.3. In case of mistake Spock protests with a clear error message: Could not instantiate global transform class org.spockframework.compiler.SpockTransform specified at jar:file:/home/foo/.../spock-core-1.0-groovy-2.3.jar!/META-INF/services/org.codehaus.groovy.transform.ASTTransformation because of exception org.spockframework.util.IncompatibleGroovyVersionException: The Spock compiler plugin cannot execute because Spock 1.0.0-groovy-2.3 is not compatible with Groovy 2.4.0. For more information, see http://versioninfo.spockframework.org Together with other mandatory pom.xml elements the file size increased to over 50 lines of XML. Quite much just for Groovy and Spock. Let’s see how complicated it is in Gradle. Gradle Gradle has built-in support for Groovy and Scala. Without further ado Groovy plugin just has to be applied. apply plugin: 'groovy' Next the dependencies has to be added: compile 'org.codehaus.groovy:groovy-all:2.4.1' testCompile 'org.spockframework:spock-core:1.0-groovy-2.4' and the information where Gradle should look for them: repositories { mavenCentral() } Together with defining package group and version it took 15 lines of code in Groovy-based DSL. Btw, in case of Gradle it is also very important to match Spock and Groovy version, e.g. Groovy 2.4.1 and Spock 1.0-groovy-2.4. Summary Thanks to embedded support for Groovy and compact DSL Gradle is preferred solution to start playing with Spock (and Groovy in general). Nevertheless if you prefer Apache Maven with a help of GMavenPlus (and XML) it is also possible to build project tested with Spock. The minimal working project with Spock 1.0 and Groovy 2.4 configured in Maven and Gradle can be cloned from my GitHub. Note 1. I haven’t been using Maven in my project for over 2 years (I prefer Gradle), so if there is a better/easier way to configure Groovy and Spock with Maven just let me know in the comments. Note 2. The configuration examples assume that Groovy is used only for tests and the production code is written in Java. It is possible to mix Groovy and Java code together, but then the configuration is a little more complicated.

Problem 1: Multiple Asserts Using multiple asserts are not good practice because if first one fail and the remaining asserts will not reach example: Assert.assertEquals("Field1", mock.field1); Assert.assertEquals(expectedField2, mock.field2); Assert.assertEquals(expectedField3, mock.field3); Assert.assertEquals(expectedField4, mock.field4); Problem 2: Single Assert with && operator condition Problem 1 can achieve by combining multiple conditions by using && operator but the issue is to difficult know which one is failed. Assert.assertTrue("Field1".equals(mock.field1) && expectedField2==mock.field2 && expectedField3==mock.field3 && expectedField4==mock.field4); Solution: by creating simple builder class can address the above two issues. in this example add method has third argument i.e label and it will tell whenever assertion failed in particular condition. Example: The below JUNIT code will fail because expected "Field2" but we got "Field1" The assertion failure message show like this, java.lang.AssertionError: expected:<[Field2]> but was <[Field1]> failed at Field1 EqualsBuilder eqb = EqualsBuilder.newBuilder() .and("Field2",mock.field1,"Field1").and(expectedField2, mock.field2,"Field2") .and(expectedField3, mock.field3,"Field3").and(expectedField4, mock.field4,"Field4"); Assert.assertTrue(eqb.getMessage(),eqb.result()); complete code is here. EqualsBuilder.java package com.demo; import java.text.MessageFormat; /** * @author UpenderC * */ public class EqualsBuilder { private boolean result = true; private String text=""; public static EqualsBuilder newBuilder() { return new EqualsBuilder(); } /** * @param expected * @param actual * @param msg * @return * example: */ public EqualsBuilder and(final Object expected,final Object actual, final String msg) { result = result && actual!=null && expected!=null ? expected.equals(actual):false; if (!result && text.length()<1) { text = MessageFormat.format("expected:<[{0}]> but was <[{1}]> failed at {2}",expected,actual,msg); } return this; } public boolean result() { return result; } public String getMessage() { return text; } } MultipleAssertsTest.java package com.stewi.demo; import java.util.Date; import org.junit.Assert; import org.junit.Test; import org.junit.runner.RunWith; import org.junit.runners.JUnit4; @RunWith(JUnit4.class) public class MultipleAssertsTest { @Test public void multipleAsserts() { Date expectedField4 = new Date(); Integer expectedField2 = 1; Long expectedField3 =2000000000l; MockFields mock = getMock(1); /*example1: Assert.assertEquals("Field1", mock.field1); Assert.assertEquals(expectedField2, mock.field2); Assert.assertEquals(expectedField3, mock.field3); Assert.assertEquals(expectedField4, mock.field4);*/ /* example2: * Assert.assertTrue("Field1".equals(mock.field1) && expectedField2==mock.field2 && expectedField3==mock.field3 && expectedField4==mock.field4); */ //example3: EqualsBuilder eqb = EqualsBuilder.newBuilder() .and("Field2",mock.field1,"Field1").and(expectedField2, mock.field2,"Field2") .and(expectedField3, mock.field3,"Field3").and(expectedField4, mock.field4,"Field4"); Assert.assertTrue(eqb.getMessage(),eqb.result()); } private MockFields getMock(int scenario) { switch(scenario) { case 1: MockFields iMock1 = new MockFields(); iMock1.field1="Field1"; iMock1.field2=1; iMock1.field3=2000000000l; iMock1.field4=new Date(); return iMock1; case 2: MockFields iMock2 = new MockFields(); return iMock2; default: return null; } } } /** * just created mock , in real time this class may generated by * third party and doesn't have equals method to compare complete * object * */ class MockFields { public String field1; public Integer field2; public Long field3; public Date field4; }

What does implementing microservices mean for a software developer? Especially, for the rookies, greenhorns, and newbs out there? I’m not talking about microservice software architecture here; this is about microservices software development. And not just that, the ultimate implementation goal should be “microservices done right”. For this post, I’ll go with Java. Yes, it’s wordy. Yes, it’s resource intensive (especially when used for the sole purpose of returning a single string). However the concept of classes and objects goes well with my intention of explaining how to do microservices correctly. Plus, it makes sense to use microservices in environments that are heavily biased towards Java. Anyway, please feel free to add your own “Hello, World!” microservice in your favorite language in the comments section below. Hello, monolith! As a prerequisite, you should be familiar with the following piece of code, what it does, and why it has to look the way it does (read this tutorial if you don’t): class Starter { public static void main(String[] args) { System.out.println(“Hello, World!”); } } This is a simple console application that yields the string “Hello, World!” This is not written in the microservice way. This is an example of when not to use the microservices approach: if all you need on your console is a single string, this is all you need. Hello, code duplication! In addition to this console application, I want this string to be available on the web by calling http://localhost:80/helloWorld.servlet from a browser. Here is the required code, implemented as plain HTTP servlet (yes, it’s wordy. Get over it.) class HelloWorldServlet extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.getWriter().println(“Hello, World!”); } } The string “Hello, World!” has to be “implemented” again. Sure, this is no big deal. But this simple string could be so much more. It could be the result of a complex calculation or it could be the result of a time consuming search query. So, just imagine that the string “Hello, World!” is the result of a week’s worth of hard work (If you’re new to programming, it may very well be...). How should you go about making it available to apps and services that you create? Step 1: HelloWorldService.java To save yourself from duplicating a week’s worth of coding, allow me to introduce the HelloWorldService class: class HelloWorldService { public String greet() { return “Hello, World!”; } } You can re-use this fine piece of software craftmanship in all your apps and classes without re-implementing or duplicating code. Here’s our console application again: class Starter { HelloWorldService helloWorldService = new HelloWorldService(); public static void main(String[] args) { String message = helloWorldService.greet(); System.out.println(message); } } The same goes for servlets: class HelloWorldServlet extends HttpServlet { HelloWorldService helloWorldService = new HelloWorldService(); public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String message = helloWorldService.greet(); response.getWriter().println(message); } } It also works great for Spring MVC controllers: @Controller class HelloWorldController { HelloWorldService helloWorldService = new HelloWorldService(); @RequestMapping("/helloWorld") public String greet() { String message = helloWorldService.greet(); return message; } } I could go on and show more examples, but I think you get the point (spoiler: it’s the bold lines that matter). Those of you who are familiar with microservices could point out that this may be fine for getting rid of code duplication, but this is no microservice. You’re right, but to get to “microservices done right,” you have to be able to separate you app’s concerns, which is what I did here in the most possible basic way: I separated the app’s frontend concerns from its backend concerns. The frontend is either a console app or a servlet, the backend is HelloWorldService. Serviceward, ho! To go down microservice lane from here, all we have to do is wrap HelloWorldService into some kind of web component that makes it accessible via HTTP, right? Let’s see… First, we could just use our servlet code from above, as it conveniently returns the string as a response to any HTTP request. But we won’t. Why? Because there’s something missing: fault tolerance. What could possibly fail when returning a simple string? That’s not the point. What matters is that the client side (the code that calls HelloWorldService) should be given enough information to effectively react to failures. We face two possible problems: The service as a whole may be unavailable The service may be unable to return a proper response The service is unavailable If a service is unavailable, it’s the client that is responsible for dealing with the situation. Frameworks like unirest.io save you the effort of writing many lines of code when dealing with HTTP requests. Future> future = Unirest.post("HTTP://helloworld.myservices.local/greet") .header("accept", "application/json") .asJsonAsync(new Callback() { public void failed(UnirestException e) { //tell them UI folks that the request went south } public void completed(HttpResponse response) { //extract data from response and fulfill it’s destiny } public void cancelled() { //shot a note to UI dept that the request got cancelled } } ); With this code, the client now knows when the service is not available or has timed out following no response. Wee can easily have an error message displayed in place of the string we expected to receive. Try/catch is probably the right solution here. Invalid responses however pose more of a challenge. The service fails If the service fails, we can just return a string with an appropriate error message. But how can you know if a message is an error message or a correct response? Yes, you can start every error message with [ERROR] or invent another “smart” (read: not-so-smart) workaround, but this won’t be a solution you’ll be proud of. And, there’s always the possibility that even valid responses may begin with ERROR because it’s simply part of the message. I’d go with JSON or XML for wrapping the answer. I prefer JSON because it’s a little less wordy than XML. And I really like using the JSON-HTML tool over at json.bloople.net for visualizing results during development. Of course, you might go for any of the numerous alternatives, like protobuf or a proprietary solution of your own. The main point is that you need to be able to apply structure to responses: { “status”:”ok”, ”message”:”Hello, World!” } By checking the status attribute, you can easily decide whether to handle an error or to display an appropriate message. { “status”:”error”, ”message”:”Invalid input parameter” } The possibilities are endless here. You can add an error code or additional properties. This all boils down to a single important point: apply structure to your responses. Structure, why? Because structure not only helps you keep your code maintainable, it also serves as the foundation of the API of your service. An API definition consists of more than a URL like this: GET HTTP://helloworld.myservices.local/greet API definitions also consist of the response structures that can be expected as a response (you know this already from a few lines back): { “status”:”ok”, ”message”:”Hello, World!” } Most important takeaway Keeping the API specifications of a service’s request and response stable is a key requirement for succeeding with microservices. Conclusion Are you (and your project) ready for microservices? If you read this and kept asking yourself, what good is all the overhead of microservices, then either your project won’t benefit from microservices or you’re just not there yet (for mindset perspective see my previous post about the value of microservices ). If you can’t stop thinking about microservices, then you probably are ready.

RESTEasy (and Jersey as well) contain a minimal web server within their libraries which enables their users to start up a tiny web server.

As a long time Java application developer working in variety of corporate environments one of the common activities I have to perform is to write mappings to translate one Java model object into another. Regardless of the technology or library I use to write the mapper, the same question comes up. What is the best way to unit test it? I've been through various approaches, all with a variety of pros and cons related to the amount of time it takes to write what is essentially a pretty simple test. The tendency (I hate to admit) is to skimp on testing all fields and focus on what I deem to be the key fields in order to concentrate on, dare I say it, more interesting areas of the codebase. As any coder knows, this is the road to bugs and the time spent writing the test is repaid many times over in reduced debugging later. Enter eXpectamundo eXpectamundo is an open source Java library hosted on github that takes a new approach to testing model objects. It allows the Java developer to write a prototype object which has been set up with expectations. This prototype can then be used to test the actual output in a unit test. The snippet below illustrates the setup of the prototype. ... User expected = prototype(User.class); expect(expected.getCreateTs()).isWithin(1, TimeUnit.SECONDS, Moments.today()); expect(expected.getFirstName()).isEqualTo("John"); expect(expected.getUserId()).isNull(); expect(expected.getDateOfBirth()).isComparableTo(AUG(9, 1975)); expectThat(actual).matches(expected); .. For a complete example lets take a simple Data Transfer Object (DTO) which transfers the definition of a new user from a UI. package org.exparity.expectamundo.sample.mapper; import java.util.Date; public class UserDTO { private String username, firstName, surname; private Date dateOfBirth; public UserDTO(String username, String firstName, String surname, Date dateOfBirth) { this.username = username; this.firstName = firstName; this.surname = surname; this.dateOfBirth = dateOfBirth; } public String getUsername() { return username; } public String getFirstName() { return firstName; } public String getSurname() { return surname; } public Date getDateOfBirth() { return dateOfBirth; } } This DTO needs to mapped into the domain model User object which can then be manipulated, stored, etc by the service layer. The domain User object is defined as below: package org.exparity.expectamundo.sample.mapper; import java.util.Date; public class User { private Integer userId; private Date createTs = new Date(); private String username, firstName, surname; private Date dateOfBirth; public User(String username, String firstName, String surname, final Date dateOfBirth) { this.username = username; this.firstName = firstName; this.surname = surname; this.dateOfBirth = dateOfBirth; } public Integer getUserId() { return userId; } public Date getCreateTs() { return createTs; } public String getUsername() { return username; } public String getFirstName() { return firstName; } public String getSurname() { return surname; } public Date getDateOfBirth() { return dateOfBirth; } } The code for the mapper is simple so we'll use a simple hand coded mapping layer however I've introduced a bug into the mapper which we'll detect later with our unit test. package org.exparity.expectamundo.sample.mapper; public class UserDTOToUserMapper { public User map(final UserDTO userDTO) { return new User(userDTO.getUsername(), userDTO.getSurname(), userDTO.getFirstName(), userDTO.getDateOfBirth()); } } We then write a unit test for the mapper using eXpectamundo to test the expectation. package org.exparity.expectamundo.sample.mapper; import java.util.concurrent.TimeUnit; import org.junit.Test; import static org.exparity.dates.en.FluentDate.AUG; import static org.exparity.expectamundo.Expectamundo.*; import static org.exparity.hamcrest.date.Moments.now; public class UserDTOToUserMapperTest { @Test public void canMapUserDTOToUser() { UserDTO dto = new UserDTO("JohnSmith", "John", "Smith", AUG(9, 1975)); User actual = new UserDTOToUserMapper().map(dto); User expected = prototype(User.class); expect(expected.getCreateTs()).isWithin(1, TimeUnit.SECONDS, now()); expect(expected.getFirstName()).isEqualTo("John"); expect(expected.getSurname()).isEqualTo("Smith"); expect(expected.getUsername()).isEqualTo("JohnSmith"); expect(expected.getUserId()).isNull(); expect(expected.getDateOfBirth()).isSameDay(AUG(9, 1975)); expectThat(actual).matches(expected); } } The test shows how simple equality tests can be performed and also introduced some of the specialised tests which can be performed, such as testing for null, or testing the bounds of the create timestamp and performing a comparison check on the dateOfBirth property. Running the unit test reports the failure in the mapper where the firstname and surname properties have been transposed by the mapper. java.lang.AssertionError: Expected a User containing properties : getCreateTs() is expected within 1 seconds of Sun Jan 18 13:00:33 GMT 2015 getFirstName() is equal to John getSurname() is equal to Smith getUsername() is equal to JohnSmith getUserId() is null getDateOfBirth() is comparable to Sat Aug 09 00:00:00 BST 1975 But actual is a User containing properties : getFirstName() is Smith getSurname() is John A simple fix to the mapper resolves the issue: package org.exparity.expectamundo.sample.mapper; public class UserDTOToUserMapper { public User map(final UserDTO userDTO) { return new User(userDTO.getUsername(),userDTO.getFirstName(), userDTO.getSurname(), userDTO.getDateOfBirth()); } } But I can do this with hamcrest! The hamcrest equivalent to this test would follow one of two patterns; a custom implementation of org.hamcrest.Matcher for matching User objects, or a set of inline assertions as per the following example: package org.exparity.expectamundo.sample.mapper; import java.util.concurrent.TimeUnit; import org.junit.Test; import static org.exparity.dates.en.FluentDate.AUG; import static org.exparity.hamcrest.date.DateMatchers.within; import static org.exparity.hamcrest.date.Moments.now; import static org.hamcrest.MatcherAssert.assertThat; import static org.hamcrest.Matchers.*; public class UserDTOToUserMapperHamcrestTest { @Test public void canMapUserDTOToUser() { UserDTO dto = new UserDTO("JohnSmith", "John", "Smith", AUG(9, 1975)); User actual = new UserDTOToUserMapper().map(dto); assertThat(actual.getCreateTs(), within(1, TimeUnit.SECONDS, now())); assertThat(actual.getFirstName(), equalTo("John")); assertThat(actual.getSurname(), equalTo("Smith")); assertThat(actual.getUsername(), equalTo("JohnSmith")); assertThat(actual.getUserId(), nullValue()); assertThat(actual.getDateOfBirth(), comparesEqualTo(AUG(9, 1975))); } } In this example the only difference eXpectamundo offers over hamcrest is a different way of reporting mismatches. eXpectamundo will report all differences between the expected vs the actual whereas the hamcrest test will fail on the first difference. An improvement, but not really a reason to consider alternatives. Where the approach eXpectomundo offers starts to differentiate itself is when testing more complex object collections and graphs. Collection testing with eXpectamundo If we move our code forward and we create a repository to allow us to store and retrieve User instances. For the sake of simplicity I've used a basic HashMap backed repository. The code for the repository is as follows: package org.exparity.expectamundo.sample.mapper; import java.util.*; public class UserRepository { private Map userMap = new HashMap<>(); public List getAll() { return new ArrayList<>(userMap.values()); } public void addUser(final User user) { this.userMap.put(user.getUsername(), user); } public User getUserByUsername(final String username) { return userMap.get(username); } } We then write a unit test to confirm the behaviour of repository package org.exparity.expectamundo.sample.mapper; import java.util.Date; import java.util.concurrent.TimeUnit; import org.junit.Test; import static org.exparity.dates.en.FluentDate.AUG; import static org.exparity.expectamundo.Expectamundo.*; public class UserRepositoryTest { private static String FIRST_NAME = "John"; private static String SURNAME = "Smith"; private static String USERNAME = "JohnSmith"; private static Date DATE_OF_BIRTH = AUG(9, 1975); private static User EXPECTED_USER; static { EXPECTED_USER = prototype(User.class); expect(EXPECTED_USER.getCreateTs()).isWithin(1, TimeUnit.SECONDS, new Date()); expect(EXPECTED_USER.getFirstName()).isEqualTo(FIRST_NAME); expect(EXPECTED_USER.getSurname()).isEqualTo(SURNAME); expect(EXPECTED_USER.getUsername()).isEqualTo(USERNAME); expect(EXPECTED_USER.getUserId()).isNull(); expect(EXPECTED_USER.getDateOfBirth()).isComparableTo(DATE_OF_BIRTH); } @Test public void canGetAll() { User user = new User(USERNAME, FIRST_NAME, SURNAME, DATE_OF_BIRTH); UserRepository repos = new UserRepository(); repos.addUser(user); expectThat(repos.getAll()).contains(EXPECTED_USER); } @Test public void canGetByUsername() { User user = new User(USERNAME, FIRST_NAME, SURNAME, DATE_OF_BIRTH); UserRepository repos = new UserRepository(); repos.addUser(user); expectThat(repos.getUserByUsername(USERNAME)).matches(EXPECTED_USER); } } The test shows how the prototype, once constructed, can be used to perform a deep verification of an object and, if desired, can be re-used in multiple tests. The equivalent matcher in hamcrest is to write a custom matcher for the User object, or as below with flat objects using a multi matcher. (Note there are a number of ways to write the matcher, the one below I felt was the most terse example). package org.exparity.expectamundo.sample.mapper; import java.util.Date; import java.util.concurrent.TimeUnit; import org.hamcrest.*; import org.junit.Test; import static org.exparity.dates.en.FluentDate.AUG; import static org.exparity.hamcrest.BeanMatchers.hasProperty; import static org.exparity.hamcrest.date.DateMatchers.*; import static org.hamcrest.MatcherAssert.assertThat; import static org.hamcrest.Matchers.*; public class UserRepositoryHamcrestTest { private static String FIRST_NAME = "John"; private static String SURNAME = "Smith"; private static String USERNAME = "JohnSmith"; private static Date DATE_OF_BIRTH = AUG(9, 1975); private static final Matcher EXPECTED_USER = Matchers.allOf( hasProperty("CreateTs", within(1, TimeUnit.SECONDS, new Date())), hasProperty("FirstName", equalTo(FIRST_NAME)), hasProperty("Surname", equalTo(SURNAME)), hasProperty("Username", equalTo(USERNAME)), hasProperty("UserId", nullValue()), hasProperty("DateOfBirth", sameDay(DATE_OF_BIRTH))); @Test public void canGetAll() { User user = new User(USERNAME, FIRST_NAME, SURNAME, DATE_OF_BIRTH); UserRepository repos = new UserRepository(); repos.addUser(user); assertThat(repos.getAll(), hasItem(EXPECTED_USER)); } @Test public void canGetByUsername() { User user = new User(USERNAME, FIRST_NAME, SURNAME, DATE_OF_BIRTH); UserRepository repos = new UserRepository(); repos.addUser(user); assertThat(repos.getUserByUsername(USERNAME), is(EXPECTED_USER)); } } In comparison this hamcrest-based test matches the eXpectamundo test in compactness but not in type-safety. A type-safe matcher can be created which checks each property individual which would make considerably more code for no benefit over the eXpectamundo equivalent. The error reporting during failures is also clear and intuitive for the eXpectamundo test, less so for the hamcrest-equivalent. (Again an equivalent descriptive test can be written using hamcrest but will require much more code). An example of the error reporting is below where the surname is returned in place of the firstname: java.lang.AssertionError: Expected a list containing a User with properties: getCreateTs() is a expected within 1 seconds of Fri Mar 06 17:29:52 GMT 2015 getFirstName() is equal to John getSurname() is equal to Smith getUsername() is equal to JohnSmith getUserId() is is null getDateOfBirth() is is comparable to Sat Aug 09 00:00:00 BST 1975 but actual list contains: User containing properties getFirstName() is Smith Summary In summary eXpectamundo offers a new approach to perform verification of models during testing. It provides a type-safe interface to set expectations making creation of deep model tests, especially in an IDE with auto-complete, particularly simple. Failures are also reported with a clear to understand error trace. Full details of eXpectamundo and the other expectations and features it supports are available on the eXpectamundo page on github. The example code is also available on github. Try it out To try eXpectamundo out for yourself include the dependency in your maven pom or other dependency manager org.exparity expectamundo 0.9.15 test

Jenkins is one of the most popular build servers and it runs on a wide variety of platforms (Windows, Linux, Mac OS X) and can build software for most programming languages (Java, C#, C++, …). And best of all, it is fully open source and free to use. By default Jenkins runs on the port 8080, which can be troublesome as this not the standard port 80 used by most web applications. But running on port 80 is in most cases not possible as the webserver is already using this port. Luckily IIS has a neat feature that allows it to act as a reverse proxy. The reverse proxy mode allows to forward traffic from IIS to another web server (Jenkins in this example) and send the responses back through IIS. This allows us to assign a regular DNS address to Jenkins and use the standard HTTP port 80. In this guide, I will explain you how you can set this up. What is required? You need an installation of IIS 7 or higher and you need to install the additional modules “URL Rewrite and “Application Request Routing”. The easiest way to install these modules is through the Microsoft Web Platform Installer. Configuring IIS Once the two necessary modules are installed, you have to create a new website in IIS. In my example I bind this website to the DNS alias “Jenkins.test.intranet”. You can bind this of course to the DNS of your choice (or to no specific DNS entry). Next you must copy the following web.config to the root of newly created website. This rule forwards all the traffic to http://localhost:8080/, the address on which Jenkins is running. It is also possible to configure this through the GUI with the URL Rewrite dialog boxes. I you are not forwarding to a localhost address, you need to go into the dialogs of Application Requet Routing and check the “Enable proxy” property.

junit != unit test Junit is the Java unit testing framework. We use it for unit testing usually, but many times we use it to execute integration tests as well. The major difference is that unit tests test individual units, while integration tests test how the different classes work together. This way integration tests cover longer execution chain. This means that they may discover more errors than unit tests, but at the same time they usually run longer times and it is harder to locate the bug if a test fails. If you, as a developer are aware of these differences there is nothing wrong to use junit to execute non-unit tests. I have seen examples in production code when the junit framework was used to execute system tests, where the execution chain of the test included external service call over the network. Junit is just a tool, so still, if you are aware of the drawbacks there is nothing inherently wrong with it. However in the actual case the execution of the junit tests were executed in the normal maven test phase and once the external service went down the code failed to build. That is bad, clearly showing the developer creating the code was not aware of the big picture that includes the external services and the build process. After having all that said, let me tell you a different story and join the two threads later. We speak languages… many Our programs have user interface, most of the time. The interface contains texts, usually in different languages. Usually in English and local language where the code is targeted. The text literals are usually externalized stored in “properties” files. Having multiple languages we have separate properties file for each language, each defining a literal text for an id. For example we have the files messages-de.properties messages-fr.properties messages-en.properties messages-pl.properties messages.properties and in the Java code we were accessing these via the Spring MessageSource calling String label = messageSource.getMessage("my.label.name",null,"label",locale); We, programmers are kind of lazy The problems came when we did not have some of the translations of the texts. The job of specifying the actual text of the labels in different languages does not belong to the programmers. Programmers are good speaking Java, C and other programming languages but are not really shining when it comes to natural languages. Most of us just do not speak all the languages needed. There are people who have the job to translate the text. Different people usually for different languages. Some of them work faster, others slower and the coding just could not wait for the translations to be ready. For the time till the final translation is available we use temporary strings. All temporary solutions become final. The temporary strings, which were just the English version got into the release. Process and discipline: failed To avoid that we implemented a process. We opened a Jira issue for each translation. When the translation was ready it got attached to the issue. When it got edited into the properties file and committed to git the issue was closed. It was such a burden and overhead that programmers were slowed down by it and less disciplined programmers just did not follow the process. Generally it was a bad idea. We concluded that not having a translation into the properties files is not the real big issue. The issue is not knowing that it was missing and creating a release. So we needed a process to check the correctness of the properties files before release. Light-way process and control Checking would have been cumbersome manually. We created junit tests that compared the different language files and checked that there is no key missing from one present in an other and that the values are not the same as the default English version. The junit test was to be executed each time when the project was to be released. Then we realized that some of the values are really the same as the English version so we started to use the letter ‘X’ at the first position in the language files to signal a label waiting for real translated value replacement. At this point somebody suggested that the junit test could be replaced by a simple ‘grep’. It was almost true, except we still wanted to discover missing keys and test running automatically during the release process. Summary, and take-away The Junit framework was designed to execute unit tests, but frameworks can and will be used not only for the purpose they were designed for. (Side note: this is actually true for any tool be it simple as a hammer or complex as default methods in Java interfaces.) You can use junit to execute tasks that can be executed during the testing phase of build and/or release. The tasks should execute fast, since the execution time adds to the build/release cycle. Should not depend on external sources, especially those that are reachable over the network, because these going down may also render the build process fail. When something is not acceptable for the build use the junit api to signal failure. Do not just write warnings. Nobody reads warnings.

These days a lot of organizations talk about Multi-Speed IT, so I thought I’d share my thoughts on this. I think the concept has been around for a while but now there is a nice label to associate this idea with. Let’s start by looking at why Multi-Speed IT is important. The idea is best illustrated by a picture of two interlocking gears of different sizes and by using a simple example to explain the concept. Different Speeds for Different Needs One easy way to recall what multi-speed IT looks like is to remember that there are multiple speeds for multiple needs. This is to say that there are different IT programs that may be most useful at various speeds. Some departments and applications need to move very rapidly, but others can move at a slower pace that works best for them. Regardless of which department you are focused on at the moment, it is important to know that it will have specialized needs that you need to look after, and that is why so many people are now looking at multi-speed IT as the best way to accomplish what they set out to accomplish. The smaller gear moves much faster than the larger one, but where the two gears interlock they remain aligned to not stop the motion. But what does this mean in reality? Think about a banking app on your mobile. Your bank might update the app on a weekly basis with new functionality like reporting and/or an improved user interface. That is a reasonable fast release cycle. The mainframe system that sits in the background and provides the mobile app with your account balance and transaction details does not have to change at the same speed. In fact, it might only have to provide a new service for the mobile app once every quarter. Nonetheless, the changes between those two systems need to align when new functionality is rolled out. However, it doesn’t mean both systems need to release at the same speed. In general, the customer-facing systems are the fast applications (Systems of Engagement, Digital) and the slower ones are the Systems of Record or backend systems. The release cycles should take this into consideration. So how do you get ready for the Multi-Speed IT Delivery Model? Release Strategy (Agile) – Identify functionality that requires changes in multiple systems and ones that can be done in isolation. If you follow an Agile approach, you can align every n-th release for releasing functionality that is aligned while the releases in between can deliver isolated changes for the fast-moving applications. Application Architecture – Use versioned interface agreements so that you can decouple the gears (read applications) temporarily. This means you can release a new version of a backend system or a front-end system without impacting the current functionality of the other. Once the other system catches up, new functionality becomes available across the system. This allows you to keep to your individual release schedule, which in turn means delivery is a lot less complex and interdependent. In the picture I used above, think of this as the clutch that temporarily disengages the gears. Technical Practices and Tools (DevOps) – If the application architecture decoupling is the clutch, then the technical practices and tools are the grease. This is where DevOps comes into the picture. The whole idea of Multi-Speed IT is to make the delivery of functionality less interdependent. On the flip side, you need to spend more effort on getting the right practices and tools in place to support this. For example, you want to make sure that you can quickly test the different interface versions with automated testing, you need to have good version control to make sure you have in place the right components for each application, and you also want to make sure you can manage your code line very well through abstractions and branching where required. And the basics of configuration management, packaging, and deployment will become even more important as you want to reduce the number of variables you have to deal with in your environments. You better remove those variables introduced through manual steps by having these processes completely automated. Testing strategies – Given that you are now dealing with multiple versions of components being in the environment at the same time, you have to rethink your testing strategies. The rules of combinatorics make it very clear that it only takes a few different variables before it becomes unmanageable to test all permutations. So we need to think about different testing strategies that focus on valid permutations and risk profiles. After all, functionality that is not yet live requires less testing than the ones that will go live next. The above points cover the technical aspects but to get there you will also have to solve some of the organizational challenges. Let me just highlight 3 of them here: Partnership with delivery partners – It will be important to choose your partners wisely. Perhaps it helps to think of your partner ecosystem in three categories: Innovators (the ones who work with you in innovative spaces and with new technologies), Workhorses(the ones who support your core business applications that continue to change) and Commodities (the ones who run legacy applications that don’t require much new functionality and attention). It should be clear that you need to treat them differently in regards to contracts and incentives. I will blog later about the best way to incentivize your workhorses, the area that I see most challenges in. Application Portfolio Management - Of course, to find the right partner you first need to understand what your needs are. Look across your application portfolio and determine where your applications sit across the following dimensions: Importance to business, exposure to customers, frequency of change, and volume of change. Based on this you can find the right partner to optimize the outcome for each application. Governance – Last but not least, governance is very important. In a multi-speed IT world you will need flexible governance. One size fits all will not be good enough. You will need lightweight system-driven governance for your high-speed applications and you can probably afford a more PowerPoint/Excel-driven manual governance for your slower-changing applications. If you can run status reports of live systems (like Jira, RTC, or TFS) for your fast applications you are another step closer to mastering the multi-speed IT world.

Here I will consider two different ways of standing up a local instance of Netflix Eureka. If you are not familiar with Eureka, it provides a central registry where (micro)services can register themselves and client applications can use this registry to look up specific instances hosting a service and to make the service calls. Approach 1: Native Eureka Library The first way is to simply use the archive file generated by the Netflix Eureka build process: 1. Clone the Eureka source repository here: https://github.com/Netflix/eureka 2. Run "./gradlew build" at the root of the repository, this should build cleanly generating a war file in eureka-server/build/libs folder 3. Grab this file, rename it to "eureka.war" and place it in the webapps folder of either tomcat or jetty. For this exercise I have used jetty. 4. Start jetty, by default jetty will boot up at port 8080, however I wanted to instead bring it up at port 8761, so you can start it up this way, "java -jar start.jar -Djetty.port=8761" The server should start up cleanly and can be verified at this endpoint - "http://localhost:8761/eureka/v2/apps" Approach 2: Spring-Cloud-Netflix Spring-Cloud-Netflix provides a very neat way to bootstrap Eureka. To bring up Eureka server using Spring-Cloud-Netflix the approach that I followed was to clone the sample Eureka server application available here: https://github.com/spring-cloud-samples/eureka 1. Clone this repository 2. From the root of the repository run "mvn spring-boot:run", and that is it!. The server should boot up cleanly and the REST endpoint should come up here: "http://localhost:8761/eureka/apps". As a bonus, Spring-Cloud-Netflix provides a neat UI showing the various applications who have registered with Eureka at the root of the webapp at "http://localhost:8761/". Just a few small issues to be aware of, note that the context url's are a little different in the two cases "eureka/v2/apps" vs "eureka/apps", this can be adjusted on the configurations of the services which register with Eureka. Conclusion Your mileage with these approaches may vary. I have found Spring-Cloud-Netflix a little unstable at times but it has mostly worked out well for me. The documentation at the Spring-Cloud site is also far more exhaustive than the one provided at the Netflix Eureka site.

Deadlocks are situations in which two or more actions are waiting for the others to finish, making all actions in a blocked state forever. They can be very hard to detect during development, and they usually require restart of the application in order to recover. To make things worse, deadlocks usually manifest in production under the heaviest load, and are very hard to spot during testing. The reason for this is it’s not practical to test all possible interleavings of a program’s threads. Although some statical analysis libraries exist that can help us detect the possible deadlocks, it is still necessary to be able to detect them during runtime and get some information which can help us fix the issue or alert us so we can restart our application or whatever. Detect deadlocks programmatically using ThreadMXBean class Java 5 introduced ThreadMXBean - an interface that provides various monitoring methods for threads. I recommend you to check all of the methods as there are many useful operations for monitoring the performance of your application in case you are not using an external tool. The method of our interest is findMonitorDeadlockedThreads, or, if you are using Java 6,findDeadlockedThreads. The difference is that findDeadlockedThreads can also detect deadlocks caused by owner locks (java.util.concurrent), while findMonitorDeadlockedThreads can only detect monitor locks (i.e. synchronized blocks). Since the old version is kept for compatibility purposes only, I am going to use the second version. The idea is to encapsulate periodical checking for deadlocks into a reusable component so we can just fire and forget about it. One way to impement scheduling is through executors framework - a set of well abstracted and very easy to use multithreading classes. ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1); this.scheduler.scheduleAtFixedRate(deadlockCheck, period, period, unit); Simple as that, we have a runnable called periodically after a certain amount of time determined by period and time unit. Next, we want to make our utility is extensive and allow clients to supply the behaviour that gets triggered after a deadlock is detected. We need a method that receives a list of objects describing threads that are in a deadlock: void handleDeadlock(final ThreadInfo[] deadlockedThreads); Now we have everything we need to implement our deadlock detector class. public interface DeadlockHandler { void handleDeadlock(final ThreadInfo[] deadlockedThreads); } public class DeadlockDetector { private final DeadlockHandler deadlockHandler; private final long period; private final TimeUnit unit; private final ThreadMXBean mbean = ManagementFactory.getThreadMXBean(); private final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1); final Runnable deadlockCheck = new Runnable() { @Override public void run() { long[] deadlockedThreadIds = DeadlockDetector.this.mbean.findDeadlockedThreads(); if (deadlockedThreadIds != null) { ThreadInfo[] threadInfos = DeadlockDetector.this.mbean.getThreadInfo(deadlockedThreadIds); DeadlockDetector.this.deadlockHandler.handleDeadlock(threadInfos); } } }; public DeadlockDetector(final DeadlockHandler deadlockHandler, final long period, final TimeUnit unit) { this.deadlockHandler = deadlockHandler; this.period = period; this.unit = unit; } public void start() { this.scheduler.scheduleAtFixedRate( this.deadlockCheck, this.period, this.period, this.unit); } } Let’s test this in practice. First, we will create a handler to output deadlocked threads information to System.err. We could use this to send email in a real world scenario, for example: public class DeadlockConsoleHandler implements DeadlockHandler { @Override public void handleDeadlock(final ThreadInfo[] deadlockedThreads) { if (deadlockedThreads != null) { System.err.println("Deadlock detected!"); Map stackTraceMap = Thread.getAllStackTraces(); for (ThreadInfo threadInfo : deadlockedThreads) { if (threadInfo != null) { for (Thread thread : Thread.getAllStackTraces().keySet()) { if (thread.getId() == threadInfo.getThreadId()) { System.err.println(threadInfo.toString().trim()); for (StackTraceElement ste : thread.getStackTrace()) { System.err.println("\t" + ste.toString().trim()); } } } } } } } } This iterates through all stack traces and prints stack trace for each thread info. This way we can know exactly on which line each thread is waiting, and for which lock. This approach has one downside - it can give false alarms if one of the threads is waiting with a timeout which can actually be seen as a temporary deadlock. Because of that, original thread could no longer exist when we handle our deadlock and findDeadlockedThreads will return null for such threads. To avoid possible NullPointerExceptions, we need to guard for such situations. Finally, lets force a simple deadlock and see our system in action: DeadlockDetector deadlockDetector = new DeadlockDetector(new DeadlockConsoleHandler(), 5, TimeUnit.SECONDS); deadlockDetector.start(); final Object lock1 = new Object(); final Object lock2 = new Object(); Thread thread1 = new Thread(new Runnable() { @Override public void run() { synchronized (lock1) { System.out.println("Thread1 acquired lock1"); try { TimeUnit.MILLISECONDS.sleep(500); } catch (InterruptedException ignore) { } synchronized (lock2) { System.out.println("Thread1 acquired lock2"); } } } }); thread1.start(); Thread thread2 = new Thread(new Runnable() { @Override public void run() { synchronized (lock2) { System.out.println("Thread2 acquired lock2"); synchronized (lock1) { System.out.println("Thread2 acquired lock1"); } } } }); thread2.start(); Output: Thread1 acquired lock1 Thread2 acquired lock2 Deadlock detected! “Thread-1” Id=11 BLOCKED on java.lang.Object@68ab95e6 owned by “Thread-0” Id=10 deadlock.DeadlockTester$2.run(DeadlockTester.java:42) java.lang.Thread.run(Thread.java:662) “Thread-0” Id=10 BLOCKED on java.lang.Object@58fe64b9 owned by “Thread-1” Id=11 deadlock.DeadlockTester$1.run(DeadlockTester.java:28) java.lang.Thread.run(Thread.java:662) Keep in mind that deadlock detection can be an expensive operation and you should test it with your application to determine if you even need to use it and how frequent you will check. I suggest an interval of at least several minutes as it is not crucial to detect deadlock more frequently than this as we don’t have a recovery plan anyway - we can only debug and fix the error or restart the application and hope it won’t happen again. If you have any suggestions about dealing with deadlocks, or a question about this solution, drop a comment below.

Even though I was supposed to write a series of blog posts about micro-infra-spring here at Too Much Coding blog, today I'll write about how we've managed to decrease our biggest project's build time from 90 to 8 minutes! In one of the companies I've been working for we've faced a big problem related to pull request build times. We have one monolithic application that we are in progress of slicing into microservices but still until this process is finished we have to build that big app for each PR. We needed to change things to have really fast feedback from our build so that pull request builds don't get queued up endlessly in our CI. You can only imagine the frustration of developers who can't have their branches merged to master because of the waiting time. Structure In that project we have over 200 Gradle modules and over a dozen big projects (countries) from which we can build some (really fat) fat-jars. We have also a core module that if we change then we would have to rebuild all the big projects to check if they weren't affected by the modifications. There are a few old countries that are using GWT compilers and we have some JS tasks executed too. Initial stats Before we started to work on optimization of the process the whole application (all the countries) was built in about 1h 30 minutes. Current build time: ~90 minutes. Profile your build First thing that we've done was to run the build with the --profile switch. ./gradlew clean buildAll --profile That way Gradle created awesome stats for our build. If you are doing any sort of optimization then it's crucial to gather measurements and statistics. Check out this Gradle page about profiling your build for more info on that switch and features. Exclude long running tasks in dev mode It turned out that we are spending a lot of time on JS minification and on GWT compilation. That's why we have added a custom property -PdevMode to disable some long running tasks in dev mode build. Those tasks were: excluded JS minification benefit: 13 countries * ~60 secs * at least 2 modules where minification occurred ~ 26 minutes optimized GWT compilation: have permutations done for only 1 browser (by default it's done for multiple browsers) disable optimization of the compilation (-optimize 0) add the -draftCompile switch to to compile quickly with minimal optimizations benefit: about 2 minutes less on GWT compilation * sth like 5 projects with GWT ~ 10 minutes Overall gain: ~ 40 minutes. Current build time: ~50 minutes. Check out your tests Together with the one and only Adam Chudzik we have started to write our own Gradle Test Profiler (it's a super beta version ;) ) that created a single CSV with sorted tests by their execution time. We needed quick and easy gains without endless test refactoring and it turned out that it's really simple. One of our tests took 50 seconds to execute and it was testing a feature that has and will never be turned on on production. Of course there were plenty of other tests that we should take a look into (we'd have to look for test duplication, check out the test setup etc.) but it would involve more time, help of a QA and we needed quick gains. Benefit: By simple disabling this test we gained about 1 minute. Overall gain: ~ 41 minutes. Current build time: ~49 minutes. Turn on the --parallel Gradle flag at least for the compilation Even though at this point our gains were more or less 40 minutes it was still unacceptable for us to wait 40 minutes for the pull request to be built. That's why we decided to go parallel! Let's build the projects (over 200) in parallel and we'll gain a lot of time on that. When you execute the Gradle build with the --parallel flag Gradle calculates how many threads can be used to concurrently build the modules. For more info go to the Gradle's documentation on parallel project execution. It's an incubating feature so wen we started to get BindExceptions on port allocation we initially thought that most likely it's Gradle's fault. Then we had a chat with Szczepan Faberwho worked for Gradleware and it turns out that the feature is actually really mature (thx Szczepan for the help BTW :) ). We needed quick gains so instead of fixing the port binding stuff we decided only to compile everything in parallel and then run tests sequentially. ./gradlew clean buildAll -PdevMode -x test --parallel && ./gradlew buildAll-PdevMode Benefit: By doing this lame looking hack we gained ~4 mintues (on my 8 core laptop). Overall gain: ~ 45 minutes. Current build time: ~45 minutes. Don't be a jerk - just prepare your tests for parallelization This command seemed so lame that we couldn't even look at it. That's why we said - let's not be jerks and just fix the port issues. So we went through the code, randomized all the fixed ports, patched micro-infra-spring so it does the same upon Wiremock and Zookeeper instantiation and just ran the building of the project like this: ./gradlew clean buildAll-PdevMode --parallel We were sure that this is the killer feature that we were lacking and we're going to win the lottery. Much to our surprise the result was really disappointing. Benefit: Concurrent project build decreased the time by ~5 minutes. Overall gain: ~ 50 minutes. Current build time: ~40 minutes. Check out your project structure You can only imagine the number of WTFs that were there in our office. How on earth is that possible? We've opened up htop, iotop and all the possible tools including vmstat to see what the hell was going on. It turned out that context switching is at an acceptable level whereas at some point of the build only part of the cores are used as if sth was executed sequentially! The answer to that mystery was pretty simple. We had a wrong project structure. We had a module that ended up as a test-jar in testCompile dependency of other projects. That means that the vast majority of modules where waiting for this project to be built. Built means compiled and tested. It turned out that this test-jar module had also plenty of slow integration tests in it so only after those tests were executed could other modules be actually built! Simple source moving can drastically increase your speed By simply moving those slow tests to a separate module we've unblocked the build of all modules that were previously waiting. Now we could do further optimization - we've split the slow integration tests into two modules to make all the modules in the whole project be built in more or less equal time (around 3,5 minutes). . Benefit: Fixing the project structure decreased the time by ~10 minutes Overall gain: ~ 60 minutes. Current build time: ~30 minutes. Don't save on machine power We've invested in some big AWS instance with 32 cores and 60 gb of RAM to really profit from the parallel build's possibilities. We're paying about 1.68$ per one hour of such machine's (c3.8xlarge) working time. If someone form the management tells you that that machine costs a lot of money and the company can't afford it you can actually do a fast calculation. You can ask this manager what is more expensive - paying for the machine or paying the developer for 77 minutes * number of builds of waiting? Benefit: Paying for a really good machine on AWS decreased the build time by ~22 minutes Overall gain: ~ 82 minutes. Current build time: ~8 minutes. What else can we do? Is that it? Can we decrease the time further on? Sure we can! Possible solutions are: Go through all of the tests and check why some of them take so long to run Go through the integration tests and check if don't duplicate the logic - we will remove them We're using Liquibase for schema versioning and we haven't merged the changests for some time thus sth like 100 changesets are executed each time we boot up Spring context (it takes more or less 30 seconds) We could limit the Spring context scope for different parts of our applications so that Spring boots up faster Buy a more powerful machine ;) There is also another, better way ;) SPLIT THE MONOLITH INTO MICROSERVICES AND GO TO PRODUCTION IN 5 MINUTES ;) Summary Hopefully I've managed to show you how you can really speed up your build process. The work to be done is difficult, sometimes really frustrating but as you can see very fruitful.

Microservices is a new software architecture and delivery paradigm, where applications are composed of several small runtime services. The current mainstream approach for software delivery is to build, integrate, and test entire applications as a monolith. This approach requires any software change, however small, to require a full test cycle of the entire application. With Microservices a software module is delivered as an independent runtime service with a well defined API. The Microservices approach allow faster delivery of smaller incremental changes to an application. There are several tradeoffs to consider with the Microservices architecture. On one hand, the Microservices approach builds on several best practices and patterns for software design, architecture, and DevOps style organization. On the other hand, Microservices requires expertise in distributed programming and can become an operational nightmare without proper tooling in place. There are several good posts that highlight the pros-and-cons of Microservices, and I have added in the references section. In the remainder of this post, I will define five architectural constraints (principles that drive desired properties) for the Microservices architectural style. To be a Microservice, a service must be: Elastic Resilient Composable Minimal, and; Complete Microservice Constraint #1 - Elastic A microservice must be able to scale, up or down, independently of other services in the same application. This constraint implies that based on load, or other factors, you can fine tune your applications performance, availability, and resource usage. This constraint can be realized in different ways, but a popular pattern is to architect the system so that you can run multiple stateless instances of each microservice, and there is a mechanism for Service naming, registration, and discovery along with routing and load-balancing of requests. Microservice Constraint #2 - Resilient A microservice must fail without impacting other services in the same application. A failure of a single service instance should have minimal impact on the application. A failure of all instances of a microservice, should only impact a single application function and users should be able to continue using the rest of the application without impact. Adrian Cockroft describes Microservices as loosely coupled service oriented architecture with bounded contexts [3]. To be resilient a service has to be loosely coupled with other services, and a bounded context limits a service’s failure domain. Microservice Constraint #3 - Composable A microservice must offer an interface that is uniform and is designed to support service composition. Microservice APIs should be designed with a common way of identifying, representing, and manipulating resources, describing the API schema and supported API operations. The ‘Uniform Interfaces constraint of the REST architectural style describes this in detail. Service Composition is a SOA principle that has fairly obvious benefits, but few guidelines on how it can be achieved. A Microservice interface should be designed to support composition patterns like aggregation, linking, and higher-level functions such as caching, proxies and gateways. I previously discussed REST constraints and elements in as two part blog post: REST is not about APIs Microservice Constraint #4 - Minimal A microservice must only contain highly cohesive entities In software, cohesion is a measure of whether things belong together. A module is said to have high cohesion if all objects and functions in it are focused on the same tasks. Higher cohesion leads to more maintainable software. A Microservice should perform a single business function, which implies that all of its components are highly cohesive. This is also an Single Responsibility Principle (SRP) of object-oriented design [5] Microservice Constraint #5 - Complete A microservice must be functionally complete Bjarne Stroustrup, the creator of C++, stated that a good interface must be, “minimal but complete” i.e. as small as possible, and no smaller. Similarly, a Microservice must offer a complete function, with minimal dependencies (loose coupling) to other services in the application. This is important, as otherwise its becomes impossible to version and upgrade individual services. This constraint is designed to oppose the minimal constraint. Put together a microservice must be “minimal but complete.” Conclusions Designing a Microservices application requires application of several principles, patterns, and best practices of modular design and service-oriented architectures. In this post, I've outlined five architectural constraints which can help guide and retain the key benefits of a Microservices-style architecture. For example, Microservices Constraint# 1 - Elastic steers implementations towards separating the data tier from the application tier, and leads to stateless services. At Nirmata we have built our solution, that makes it easy to deploy and operate microservices applications, using these very same principles. We believe that Microservices style applications, running in containers, will power the next generation of software innovation. If you are using, or interested in using microservices, I would love to hear from you. Jim Bugwadia Founder and CEO Nirmata -- For additional content and articles follow us at @NirmataCloud. -- If you are in the San Francisco Bay Area, come join our Microservices meetup group. References [1] Microservices, Martin Fowler and James Lewis, http://martinfowler.com/articles/microservices.html [2] Microservices Are Not a free lunch!, Benjamin Wootton, http://contino.co.uk/microservices-not-a-free-lunch/ [3] State of the Art in Microservices, Adrian Cockroft, http://thenewstack.io/dockercon-europe-adrian-cockcroft-on-the-state-of-microservices/ [4] The Principles of Object-Oriented Design, Robert C. Martin, http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

Of late, I have been looking into Microservice containers that are available out there to help speed up the development. Although, Microservice is a generic term however there is some consensus with respect to what it means. Hence, we may conveniently refer to the definition Microservice as an "architectural design pattern, in which complex applications are composed of small, independent processes communicating with each other using language-agnostic APIs. These services are small, highly decoupled and focus on doing a small task." There are several Microservice containers out there. However, in my experience I have found Dropwizard and Spring-boot to have had received more attention and they appear to be widely used compared to the rest. In my current role, I was asked create a comparison matrix between the two, so it's here below. Dropwizard Spring-Boot What is it? Dropwizard pulls together stable, mature libraries from the Java ecosystem into a simple, light-weight package that lets you focus on getting things done. [more...] Takes an opinionated view of building production-ready Spring applications. Spring Boot favours convention over configuration and is designed to get you up and running as quickly as possible. [more...] Overview? Dropwizard straddles the line between being a library and a framework. Provide performant, reliable implementations of everything a production-ready web application needs. [more...] Spring-boot takes an opinionated view of the Spring platform and third-party libraries so you can get started with minimum fuss. Most Spring Boot applications need very little Spring configuration. [more...] Out of the box features? Dropwizard has out-of-the-box support for sophisticated configuration, application metrics, logging, operational tools, and much more, allowing you and your team to ship a production-quality web service in the shortest time possible. [more...] Spring-boot provides a range of non-functional features that are common to large classes of projects (e.g. embedded servers, security, metrics, health checks, externalized configuration). [more...] Libraries Core: Jetty, Jersey, Jackson and Matrics Others: Guava, Liquibase and Joda Time. Spring, JUnit, Logback, Guava. There are several starter POM files covering various use cases, which can be included in the POM to get started. Dependency Injection? No built in Dependency Injection. Requires a 3rd party dependency injection framework such as Guice, CDI or Dagger. [Ref...] Built in Dependency Injection provided by Spring Dependency Injection container. [Ref...] Types of Services i.e. REST, SOAP Has some support for other types of services but primarily is designed for performant HTTP/REST LAYER. If ever need to integrate SOAP, there is a dropwizard bundle for building SOAP web services using JAX-WS API is provided here but it’s not official drop-wizard sub project. [more...] As well as supporting REST Spring-boot has support for other types of services such as JMS, Advanced Message Queuing Protocol, SOAP based Web Services to name a few. [more...] Deployment? How it creates the Executable Jar? Uses Shading to build executable fat jars, where a shaded jar spackages all classes, from all jars, into a single 'uber jar'. [Ref...] Spring-boot adopts a different approach and avoids shaded jars, as it becomes hard to see which libraries you are actually using in your application. It can also be problematic if the same filename is used in Shaded jars. Instead it uses “Nested Jar” approach where all classes from all jars do not need to be included into a single “uber jar” instead all dependent jars should be in the “lib” folder, spring loader loads them appropriately. [Ref...] Contract First Web Services? No built in support. Would have to refer to 3rd party library (CXF or any other JAX-WS implementation) if needed a solution for the Contract First SOAP based services. Contract First services support is available with the help of spring-boot-starter-ws starter application. [Ref...] Externalised Configuration for properties and YAML Supports both Properties and YAML Supports both Properties and YAML Concluding Remarks If dealing with only REST micro services, drop wizard is an excellent choice. Where Spring-boot shines is the types of services supported i.e. REST, JMS, Messaging, and Contract First Services. Not least a fully built in Dependency Injection container. Disclaimer: The matrix is purely based on my personal views and experiences, having tried both frameworks and is by no means an exhaustive guide. Readers are requested to do their own research before making a strategic decision between the two very formidable frameworks.

Fellow geeks, the following article provides an overview of injection in Java EE and describes the two injection mechanisms provided by the platform: Resource Injection and Dependency Injection. Java EE provides injection mechanisms that enable our objects to obtain the references to resources and other dependencies without having to instantiate them directly (explicitly with ‘new’ keyword). We simply declare the needed resources & other dependencies in our classes by drawing fields or methods with annotations that denotes the injection point to the compiler. The container then provides the required instances at runtime. The advantage of Injection is that it simplifies our code and decouples it from the implementations of its dependencies. Note should be given for the fact that Dependency Injection is a specification (also a design pattern) and Context and Dependency Injection (CDI) is an implementation andJava standard for DI. The following topics are discussed here: · Resource Injection · Dependency Injection · Difference between Context and Dependency Injection 1. Resource Injection One of the simplification features of Java EE is the implementation of basic Resource Injection to simplify web and EJB components. Resource injection enables you to inject any resource available in the JNDI namespace into any container-managed object, such as a servlet, an enterprise bean, or a managed bean. For eg, we can use resource injection to inject data sources, connectors, or any other desired resources available in the JNDI namespace. The type we’ll use for the reference to the instance happen to be injected is usually an interface, which would decouple our code from the implementation of the resource. For better understanding of the above statement let’s take a look at the example. The resource injection can be performed in the following three ways: · Field Injection · Method Injection · Class injection Now, the javax.annotation.Resource annotation is used to declare a reference to a resource. So before proceeding, let’s learn few elements of @Resource annotation. @Resource has the following elements: · name: The JNDI name of the resource · type: The Java type of the resource · authenticationType: The authentication type to use for the resource · shareable: Indicates whether the resource can be shared · mappedName: A non-portable, implementation-specific name to which the resource should be mapped · description: The description of the resource Thenameelement is the JNDI name of the resource, and is optional for field- and method-based injection. For field injection, d defaultnameis the field name. For method-based injection, the defaultnameis the JavaBeans property name based on the method. The‘name’ and ‘type’element must be specified for class injection. Thedescriptionelement is the description of the resource (optional). Let’s hop on to the example now. Field Injection: To use field-based resource injection, declare a field and annotate it with the @Resource annotation. The container will refer the name and type of the resource if the name and type elements are not specified. If you do specify the type element, it must match the field’s type declaration. package com.example; public class SomeClass { @Resource private javax.sql.DataSource myDB; ... } In the code above, the container infers the name of the resource based on the class name and the field name: com.example.SomeClass/myDB. The inferred type isjavax.sql.DataSource.class. package com.example; public class SomeClass { @Resource(name="customerDB") private javax.sql.DataSource myDB; ... } In the code above, the JNDI name is customerDB, and the inferred type is javax.sql.DataSource.class. Method Injection: To use method injection, declare a setter method and preceding with the @Resource annotation. The container will itself refer the name and type of the resource if in case it is not specified by programmer. The setter method must follow the JavaBeans conventions for property names: the method name must begin with set, have a void return type, and only one parameter (needless to say :P). Anyways, if you do specify the return type, it must match the field’s type declaration. package com.example; public class SomeClass { private javax.sql.DataSource myDB; ... @Resource private void setMyDB(javax.sql.DataSource ds) { myDB = ds; } ... } In the code above, the container refers the name of the resource according to the class name and the field name: com.example.SomeClass/myDB. The type which is javax.sql.DataSource.class. package com.example; public class SomeClass { private javax.sql.DataSource myDB; ... @Resource (name="customerDB") private void setMyDB (javax.sql.DataSource ds) { myDB = ds; } ... } In the code above, the JNDI name is customerDB, and the inferred type is javax.sql.DataSource.class. Class Injection: To use class-based injection, decorate the class with a @Resource annotation, and set the requiredname and type elements. @Resource(name="myMessageQueue", type="javax.jms.ConnectionFactory") public class SomeMessageBean { ... } Declaring Multiple Resources The @Resources annotation is used to group together multiple @Resource declarations for class injection only. @Resources({ @Resource(name="myMessageQueue", type="javax.jms.ConnectionFactory"), @Resource(name="myMailSession", type="javax.mail.Session") }) public class SomeMessageBean { ... } The code above shows the @Resources annotation containing two @Resource declarations. One is a JMS (Java Messagin Service) message queue, and the other is a JavaMail session. 2. Dependency Injection Dependency injection enables us to turn regular Java classes into managed objects and to inject them into any other managed object (objects wich are managed by the container). Using DI, our code can declare dependencies on any managed object. The container automatically provides instances of these dependencies at the injection points at runtime, n it also manages the lifecycle of these instances right from class loading to releasing it for Garbage Collection. Dependency injection in Java EE defines scopes. For eg, a managed object that is only happen to respond to a single client request (such as a currency converter) has a different scope than a managed object that is needed to process multiple client requests within a session (such as a shopping cart). We can define managed objects (also called managed beans) so that we can later inject by assigning a scope to a needed class: @javax.enterprise.context.RequestScoped public class CurrencyConverter { ... } Use the javax.inject.Inject annotation to inject managed beans; for example: public class MyServlet extends HttpServlet { @Inject CurrencyConverter cc; ... } Umlike resource injection, dependency injection is typesafe because it resolves by type. To decouple our code from the implementation of the managed bean, we can reference the injected instances using an interface type and have our managed bean (regular class controlled by container) implement that interface. I wouldn’t like to discuss more on DI or better saying CDI since we already have a great article published on this. 3. Difference between Resource Injection and Dependency Injection The differences between the RI and DI are listed below. 1. Resource Injection can inject JNDI Resources directly whereas Dependency Injection cannot. 2. Dependency Injection can inject Regular Classes (managed bean) directly whereas Resource Injection cannot. 3. Resource Injection resolves by resource name whereas Dependency Injectin resolves by type. 4. Dependency Injection is typesafe whereas Resoiurce Injection is not. Conclusion: Thus we learnt concept on types on Injection in Java EE and the differences between them. Just a brief. There’s more to come

If you go to Google and search for "measuring software developer productivity" you will find a whole lot of nothing. Seriously -- nothing. Nick Hodges, Measuring Developer Productivity By now we should all know that we don’t know how to measure programmer productivity. There is no clear cut way to measure which programmers are doing a better or faster job, or to compare productivity across teams. We “know” who the stars on a team are, who we can depend on to deliver, and who is struggling. And we know if a team is kicking ass – or dragging their asses. But how do we prove it? How can we quantify it? All sorts of stupid and evil things can happen when you try to measure programmer productivity. But let’s do it anyways. We’re Writing More Code, So We Must Be More Productive Developers are paid to write code. So why not measure how much code they write – how many lines of code get delivered? Because we've known since the 1980s that this is a lousy way to measure productivity. Lines of code can’t be compared across languages (of course), or even between programmers using the same language working in different frameworks or following different styles. Which is why Function Points were invented – an attempt to standardize and compare the size of work in different environments. Sounds good, but Function Points haven’t made it into the mainstream, and probably never will – very few people know how Function Points work, how to calculate them and how they should be used. The more fundamental problem is that measuring productivity by lines (or Function Points or other derivatives) typed doesn’t make any sense. A lot of important work in software development, the most important work, involves thinking and learning – not typing. The best programmers spend a lot of time understanding and solving hard problems, or helping other people understand and solve hard problems, instead of typing. They find ways to simplify code and eliminate duplication. And a lot of the code that they do write won’t count anyways, as they iterate through experiments and build prototypes and throw all of it away in order to get to an optimal solution. The flaws in these measures are obvious if we consider the ideal outcomes: the fewest lines of code possible in order to solve a problem, and the creation of simplified, common processes and customer interactions that reduce complexity in IT systems. Our most productive people are those that find ingenious ways to avoid writing any code at all. Jez Humble, The Lean Enterprise This is clearly one of those cases where size doesn’t matter. We’re Making (or Saving) More Money, so We Must Be Working Better We could try to measure productivity at a high level using profitability or financial return on what each team is delivering, or some other business measure such as how many customers are using the system – if developers are making more money for the business (or saving more money), they must be doing something right. Using financial measures seems like a good idea at the executive level, especially now that “every company is a software company”. These are organizational measures that developers should share in. But they are not effective – or fair – measures of developer productivity. There are too many business factors are outside of the development team’s control. Some products or services succeed even if the people delivering them are doing a lousy job, or fail even if the team did a great job. Focusing on cost savings in particular leads many managers to cut people and try “to do more with less” instead of investing in real productivity improvements. And as Martin Fowler points out there is a time lag, especially in large organizations – it can sometimes take months or years to see real financial results from an IT project, or from productivity improvements. We need to look somewhere else to find meaningful productivity metrics. We’re Going Faster, so We Must Be Getting More Productive Measuring speed of development – velocity in Agile – looks like another way to measure productivity at the team level. After all, the point of software development is to deliver working software. The faster that a team delivers, the better. But velocity (how much work, measured in story points or feature points or ideal days, that the team delivers in a period of time) is really a measure of predictability, not productivity. Velocity is intended to be used by a team to measure how much work they can take on, to calibrate their estimates and plan their work forward. Once a team’s velocity has stabilized, you can measure changes in velocity within the team as a relative measure of productivity. If the team’s velocity is decelerating, it could be an indicator of problems in the team or the project or the system. Or you can use velocity to measure the impact of process improvements, to see if training or new tools or new practices actually make the team’s work measurably faster. But you will have to account for changes in the team, as people join or leave. And you will have to remember that velocity is a measure that only makes sense within a team – that you can’t compare velocity between teams. Although this doesn't stop people from trying. Some shops use the idea of a well-known reference story that all teams in a program understand and use to base their story points estimates on. As long as teams aren't given much freedom on how they come up with estimates, and as long as the teams are working in the same project or program with the same constraints and assumptions, you might be able to do rough comparison of velocity between teams. But Mike Cohn warns that If teams feel the slightest indication that velocities will be compared between teams there will be gradual but consistent “point inflation.” ThoughtWorks explains that velocity <> productivity in their latest Technology Radar: We continue to see teams and organizations equating velocity with productivity. When properly used, velocity allows the incorporation of “yesterday's weather” into a team’s internal iteration planning process. The key here is that velocity is an internal measure for a team, it is just a capacity estimate for that given team at that given time. Organizations and managers who equate internal velocity with external productivity start to set targets for velocity, forgetting that what actually matters is working software in production. Treating velocity as productivity leads to unproductive team behaviors that optimize this metric at the expense of actual working software. Next: Just Stay Busy, Measure Outcomes, not Output; and more... Just Stay Busy One manager I know says that instead of trying to measure productivity “We just stay busy. If we’re busy working away like maniacs, we can look out for problems and bottlenecks and fix them and keep going”. In this case you would measure – and optimize for – cycle time, like in Lean manufacturing. Cycle time – turnaround time or change lead time, from when the business asks for something to when they get it in their hands and see it working – is something that the business cares about, and something that everyone can see and measure. And once you start looking closely, waste and delays will show up as you measure waiting/idle time, value-add vs. non-value-add work, and process cycle efficiency (total value-add time / total cycle time). “It’s not important to define productivity, or to measure it. It’s much more important to identify non-productive activities and drive them down to zero.” Erik Simmons, Intel Teams can use Kanban to monitor – and limit – work in progress and identify delays and bottlenecks. And Value Stream Mapping to understand the steps, queues, delays and information flows which need to be optimized. To be effective, you have to look at the end-to-end process from when requests are first made to when they are delivered and running, and optimize all along the path, not just the work in development. This may mean changing how the business prioritizes, how decisions are made and who makes the decisions. In almost every case we have seen, making one process block more efficient will have a minimal effect on the overall value stream. Since rework and wait times are some of the biggest contributors to overall delivery time, adopting “agile” processes within a single function (such as development) generally has little impact on the overall value stream, and hence on customer outcomes. Jezz Humble, The Lean Enterprise The down side of equating delivery speed with productivity? Optimizing for cycle time/speed of delivery by itself could lead to problems over the long term, because this incents people to think short term, and to cut corners and take on technical debt. We’re Writing Better Software, so We Must Be More Productive “The paradox is that when managers focus on productivity, long-term improvements are rarely made. On the other hand, when managers focus on quality, productivity improves continuously.” John Seddon, quoted in The Lean Enterprise We know that fixing bugs later costs more. Whether it’s 10x or 100+x, it doesn't really matter. And that projects with fewer bugs are delivered faster – at least up to a point of diminishing returns for safety-critical and life-critical systems. And we know that the costs of bugs and mistakes in software to the business can be significant. Not just development rework costs and maintenance and support costs. But direct costs to the business. Downtime. Security breaches. Lost IP. Lost customers. Fines. Lawsuits. Business failure. It’s easy to measure that you are writing good – or bad – software. Defect density. Defect escape rates (especially defects – including security vulnerabilities – that escape to production). Static analysis metrics on the code base, using tools like SonarQube. And we know how to write good software - or we should know by now. But is software quality enough to define productivity? Devops – Measuring and Improving IT Performance Devops teams who build/maintain and operate/support systems extend productivity from dev into ops. They measure productivity across two dimensions that we have already looked at: speed of delivery, and quality. But devops isn't limited to just building and delivering code – instead it looks at performance metrics for end-to-end IT service delivery: Delivery Throughput: deployment frequency and lead time, maximizing the flow of work into production Service Quality: change failure rate and MTTR It’s not a matter of just delivering software faster or better. It’s dev and ops working together to deliver services better and faster, striking a balance between moving too fast or trying to do too much at a time, and excessive bureaucracy and over-caution resulting in waste and delays. Dev and ops need to share responsibility and accountability for the outcome, and for measuring and improving productivity and quality. As I pointed out in an earlier post this makes operational metrics more important than developer metrics. According to recent studies, success in achieving these goals lead to improvements in business success: not just productivity, but market share and profitability. Measure Outcomes, not Output In The Lean Enterprise (which you can tell I just finished reading), Jez Jumble talks about the importance of measuring productivity by outcome – measuring things that matter to the organization – not output. “It doesn't matter how many stories we complete if we don’t achieve the business outcomes we set out to achieve in the form of program-level target conditions”. Stop trying to measure individual developer productivity. It’s a waste of time. Everyone knows who the top performers are. Point them in the right direction, and keep them happy. Everyone knows the people who are struggling. Get them the help that they need to succeed. Everyone knows who doesn't fit in. Move them out. Measuring and improving productivity at the team or (better) organization level will give you much more meaningful returns. When it comes to productivity: Measure things that matter – things that will make a difference to the team or to the organization. Measures that are clear, important, and that aren't easy to game. Use metrics for good, not for evil – to drive learning and improvement, not to compare output between teams or to rank people. I can see why measuring productivity is so seductive. If we could do it we could assess software much more easily and objectively than we can now. But false measures only make things worse. Martin Fowler, CannotMeasureProductivity

We love Git Flow. It’s awesome to have a standard release process where everybody is using the same terminology and tooling. It’s also great to have out-of-the-box answers to the same questions that get asked at the start of every project. For example: “How are we going to develop features in isolation?” “How are we going to separate release candidates from ongoing development?” “How are we going to deal with hotfixes?” Now it’s enough to just say ‘We use Git Flow’, and everybody’s on the same page. Well, mostly. Whilst Git Flow is terrific for managing features and separating release candidates from ongoing development, things get a little hazier when it comes time to actually release to production. This is because of a mismatch between the way that Git Flow works and another practice that is common in large development projects: immutable build artifacts. Immutable what? On most enterprise projects I work on these days, it’s considered a pretty good idea to progress exactly the same build artifact through testing, pre-production and into production. It doesn’t matter whether it’s a JAR file, WAR file, tar.gz file, or something more exotic – the key point is that you build it once, then deploy the same thing to each downstream environment. If you find a bug during this journey, you fix the bug, build a whole new artifact, and start the process again. In the absence of any established terminology, let’s just call these things immutable build artifacts. (Note that you’ll still need a separate, external file for those things that have to be different between environments, but by keeping the amount of stuff in that file to an absolute minimum, you’ll minimise your potential exposure to variances between environments.) Without immutable build artifacts, many development managers will start to sweat nervously. This is usually because at some stage in their careers they’ve been up at 2am in the morning prising apart build artifacts and trying to understand what changed between the pre-prod build (which worked just fine) and the current prod build (which is inexplicably failing). A bunch of things can cause this sort of problem. For example, it could be that somebody managed to sneak some change in between the two builds, or that some downstream build dependency changed between the two builds, or even that somebody tweaked the build process between the two builds. ‘That’ll never happen to me’, I hear you say, ‘if everybody follows our development methodology correctly’. And therein lies the problem: it’s difficult to absolutely guarantee that a developer won’t at the last minute do something stupid, like slip something into the wrong branch, upload an incorrectly-versioned downstream dependency, or mess with your buildbox configuration. My point is this: why open yourself up to the risk at all, when having a single artifact will eliminate a whole class of potential defects? Now for the actual problem A while back, I was working on a project using both Git Flow and immutable builds. A junior developer came to me looking confused. He was trying to understand when it would be OK for him to finish the current Git Flow release. The testers had just signed off on the current build. But if he finished the release, Git Flow was going to merge the release branch into master – and strictly speaking, he should create a new build from that. But if he created a new build, the testers were going to want to test it. If they found a problem, the fix was going to have to happen in a new release branch. But then when he closed that release, he was going to have to do a new build from master, which the testers would want to test again, right? And then, if they found a bug in that… I admired his highly conscientious approach to his work, but worried that his mind was going to disintegrate as it spun around this build-management paradox. I also had to acknowledge that he had stumbled head first into something that I had been wilfully ignoring in the hope that it would resolve itself; namely, the fundamental mismatch between Git Flow and the concept of immutable builds. Put simply, Git Flow works on the premise that production builds will only be done from the master branch. In contrast, immutable builds work on the premise that production builds will be done from either a release branch or a hotfix branch. There is no perfect way to work around this mismatch. The pragmatic solution Put bluntly, if you want truly immutable builds, then you should do them from the release or hotfix branch rather than master. However, because this runs contrary to how Git Flow works, there are a couple of important consequences to keep in mind. 1. Concurrent hotfixes and releases require special handling If you start and then finish a hotfix whilst a release branch is in process, then that hotfix’s changes won’t automatically be brought into the release branch by Git Flow. This means that a subsequent build from the release branch which goes into production won’t include the hotfix changes. Here’s a diagram illustrating the problem: Note that the inverse problem would apply if you tried to start a release whilst a hotfix was in progress. Thankfully, Git Flow will not let you have two release branches in progress at the same time, so we don’t have to worry about that particular possibility. (If you’re wondering how Git Flow avoids these scenarios in its regular usage, remember that it always merges back into master when a release or hotfix is finished, and that you’re supposed to always build from master. Consequently, if you’re building from master post-release or post-hotfix, you’ll always be getting the latest changes into the build.) The problem of concurrent hotfixes and releases can be solved by merging the hotfix branch into the release branch just before the hotfix branch gets finished (or vice-versa if you started a release whilst a hotfix was in progress). Here’s what it looks like: However, you will need to remember to do this merge manually because Git Flow won’t do it for you. 2. Version tags will be incorrect by default When you finish a release or hotfix, Git Flow merges the corresponding branch back into master, and then tags the resultant merge commit on master with the version number. However, because your immutable artifact will have been built from the release/hotfix branch, the commit SHA for the version tag in Git will be different from the SHA that the artifact was actually built from. Continuing on from our previous example: You may or may not care about this, for a number of reasons. Firstly, from the perspective of Git Flow, the merge commit on master should never have any changes in it. The only scenario that might lead to it having changes is if you have run concurrent hotfix and release branches (as described in the previous section) and forgotten to merge them prior to finishing. And you’llnever forget to do that now will you? :) Secondly, in the likely event that you are using some sort of continuous integration server to produce your builds, that server can probably associate its own number with each build, and stamp the resultant artifact with that number. The CI server will probably also have recorded the SHA that each build was done from. So from the artifact you could probably work backwards to the SHA that was used to produce it. If you’re nevertheless wary of the confusion that this backtracking process might introduce when trying to debug a production issue at 2am in the morning, you might still insist on having correct version tags. In that case the best thing I can think of is to manually create the tag on the release/hotfix branch yourself before finishing it and then, when finishing the release, run git flow [release/hotfix] finish with the -n option to stop it from trying to create the tag again (which would fail because the tag now already exists). I’m on a roll with my diagrams, so what the heck, let’s do one more: Wrapping Up On balance, I think the benefits of having immutable builds outweigh the costs of deviating from the Git Flow way of doing things. However, you do have to be aware of a couple of problematic scenarios. We’ll be experimenting in coming months with using Git Flow with our own immutable builds, and will let you know if anything else weird pops up. Who knows, perhaps we’ll even end up with our own version of Git Flow. Either way, I’d be interested in hearing from anybody else who has had the same problem.

Dropwizard is a bunch of superb frameworks glued together to provide a fast way of building web applications including REST APIs. We'll talk about great frameworks which are parts of Dropwizard as we go over our examples. The full code for the examples can be obtained here . The simplest way to create a Dropwizard project is to use the Maven archetype called java-simple which is a part of Dropwizard. This can be accomplished either via the command line or using your favorite IDE. Let's stick to the former approach. The command below is formatted for clarity but it should be pasted as a single line to the terminal. mvn archetype:generate -DgroupId=com.javaeeeee -DartifactId=DWGettingStarted -Dname=DWGettingStarted -Dpackage=com.javaeeeee.dwstart -DarchetypeGroupId=io.dropwizard.archetypes -DarchetypeArtifactId=java-simple -DinteractiveMode=false After the project was created it can be modified using an editor or opened in an IDE. All the three IntelliJ, Eclipse and Netbeans have Maven support. An important parameter to note in the pom.xml file of the newly created project is dropwizard.version, which at the time of writing was automatically set to 0.8.0-rc2-SNAPSHOT and the latest stable version was 0.7.1. We'll discuss later the important consequences of the version for project development. The directory structure of the project is shown below. There are multiple sub-packages and two classes that were created for us in a package com.javaeeeee.dwstart. Now let's create a simple resource class that produces a string “Hello world!”, start the application and test the results using both browser and cURL. The snippet below shows the resource class. @Path("/hello") public class HelloResource { @GET @Produces(MediaType.TEXT_PLAIN) public String getGreeting() { return "Hello world!"; } } There is a special package, com.javaeeeee.dwstart.recources for placing resource classes or an appropriate folder can be found from the screenshot above if you use a text editor and not an IDE. One of the main tenets of the REST architecture style is that each resource is assigned a URL. In our case the URL of our resource would be http://localhost:8080/hello, that is we access it from our local machine, the default port which is used by Dropwizard is 8080 and the final part of the URL is enshrined in @Path annotation in our class, in other words, the aforementioned annotation helps to describe the URL used to access a resource. Moving on to method getGreeting() it can be seen that it is a simple method which returns the desired string “Hello world!”, although it is marked with two annotations: first, @GET prescribes that this method is called when the aforementioned URL is accessed using HTTP GET method, second, annotation @Produces specifies what media types can be produced when the method is accessed by the client, such as browser, cURL or some other program. In our case it is plain text. These annotations are part of Java API for RESTful Web Services (JAX-RS), and its reference implementation Jersey is the cornerstone of Dropwizard. Other annotations include @POST for HTTP POST method, @DELETE for DELETE and so on and media types include MediaType.APPLICATION_JSON and not so popular MediaType.APPLICATION_XML among others. Now, to see the result of our coding, we should do some configuration. Let's open one of the created by Maven files, DWGettingStartedApplication.java, and register our resource. public void run(final DWGettingStartedConfiguration configuration, final Environment environment) { environment.jersey().register(new HelloResource()); } We added a single line environment.jersey().register(new HelloResource()); to help Dropwizard find our resource class. Now we have to create a jar-file which contains an embedded Jersey web server to serve the incoming requests, as well as all the necessary libraries. Dropwizard applications are packaged as executable jar-files rather than war-files which are deployed to an application server. The kind of jar files used by Dropwizard applications are also called “fat” because they include all the .class files necessary to run the application as this leads to a situation that the versions of all libraries are the same in both development and production environments which leads to less problems. One shouldn't worry about creating such jar-files as Maven creates them for us using instructions in the generated pom.xml file of the project. The jar-file can be created using command-line command issued from the project's folder mvn package or using an IDE. After that we should start the application, which could be accomplished either from the command line by issuing a command java -jar target/DWGettingStarted-1.0-SNAPSHOT.jar server or from the IDE which can be instructed to pass a “server” argument to the executable jar file. To stop the application it is sufficient to press Ctrl+C in the terminal. Now it is time to check if it works. The simplest way to achieve this is to navigate your browser to the URL mentioned earlier. You should see the greeting string in the main window of a browser. If you cannot see the greeting, there is probably some problems and the program’s output is the place to look for clues for what went wrong. The same greeting can be seen in the terminal window with help of cURL. curl -w "\n" localhost:8080/hello Protocol HTTP and GET method are defaults, so it is not necessary that they be included explicitly in the command. As the result a message "Hello world!" without quotes should be printed. The w-option is used to add a trailing newline to prettify the output. It is a good idea to start using tests as early as possible, so let's write a test that checks the work of our resource class using in-memory Jersey. We'll create the test in test packages and as we are testing a resource an appropriate package to place our test is com.javaeeeee.dwstart.resources (or src/test/com/javaeeeee/dwstart/resources folder). It is necessary that the following dependency be added to the pom-file of the project. (It works without explicit jUnit dependency.) io.dropwizard dropwizard-testing ${dropwizard.version} test An example test for our greeting resource is shown below. public class HelloResourceTest { @Rule public ResourceTestRule resource = ResourceTestRule.builder() .addResource(new HelloResource()).build(); @Test public void testGetGreeting() { String expected = "Hello world!"; //Obtain client from @Rule. Client client = resource.client(); //Get WebTarget from client using URI of root resource. WebTarget helloTarget = client.target("http://localhost:8080/hello"); //To invoke response we use Invocation.Builder //and specify the media type of representation asked from resource. Invocation.Builder builder = helloTarget.request(MediaType.TEXT_PLAIN); //Obtain response. Response response = builder.get(); //Do assertions. assertEquals(Response.Status.OK, response.getStatusInfo()); String actual = response.readEntity(String.class); assertEquals(expected, actual); } } The annotation @Rule is from jUnit realm and could be placed on public non-static fields and methods that return a value. This annotation may perform some initial setup and clean-up like @Before and @After methods, but it is more powerful as it allows to share functionality between classes and even projects. This rule is needed to allow us to access our resources from the code of the test using in-memory Jersey. At this point of time we should pause and discuss the version of our product. There is a pom.xml file in the dropwizard folder on the GitHub, which can readily be accessed by cloning the project, and this file specifies the version of constituent products among other things. It can be seen from it that the version of Jersey in the snapshot version of Dropwizard is 2.13 and in the version 0.7.1 it is 1.18.1. The version of Jersey influences the code of the tests as 1.x and 2.x versions of Jersey have different client APIs, that is the code to access the service programmatically from Java depends on the version of Jersey framework. Let's stick to the latest 2.x version of Jersey as it is liable to be included in following 0.8.x releases of Dropwizard and if you are interested how to test using the older version of Jersey client, please check the project repository , there is a special branch v0.7.x. Another observation concerning testing is that Fest matchers were superseded by AssertJ counterparts. First, we obtain an instance of Jersey client to make requests to our service. Second, we create an instance of a class that implements WebTarget interface for the resource using its URL. After that we use Invocation.Builder that helps to build request and send it to the server. The Invocation.Builder interface extends SynchInvoker interface which defines a bunch of get(...) methods used to invoke HTTP GET method synchronously. Finally, we check the results, namely that the HTTP status code was 200 and the desired string was returned. The same result could be obtained by chaining the methods as in the snippet below. actual = resource.client() .target("http://localhost:8080/hello") .request(MediaType.TEXT_PLAIN) .get(String.class); assertEquals(expected, actual); The replacement of the two assertions by a single is possible due to the fact that the get(...) method we used throws a WebApplicationException if the HTTP status code is not in the 2xx range, in other words if there is a problem. Now let's improve our resource to take a name and return a bespoke greeting. It could be done in a couple of ways using Jersey's annotations. The first is to use so-called path parameters, that is you pass the name using a URL like http://localhost:8080/hello/path_param/your_name. The application should return “Hello your_name”. Let's see a code snippet. @Path("/path_param/{name}") @GET @Produces(MediaType.TEXT_PLAIN) public String getNamedGreeting(@PathParam(value = "name") String name) { return "Hello " + name; } Now we see a @Path annotation on our method. It adds its content to those produced by class level annotation as seen from the URL. Methods marked with this annotation are called sub-resource methods. The name of the parameter, name, is in curly braces. Something interesting happens inside the parenthesis of the getNamedGreeting method. There is an annotation which prescribes to extract the content of the url after “/path_param/” to the method as a value. It should be noted that if you find yourself marking each method with the same annotation @Produces(MediaType.TEXT_PLAIN), the latter can be removed from methods and used to mark the class, then all the methods produce the desired media types, although this can be overruled by an annotations with a different media type for some of the methods. The second way to pass a name is to use query parameters and the URL could look like http://localhost:8080/hello/query_param?name=your_name. The output should be “Hello your_name” without quotes. The snippet is shown below. @Path("/query_param") @GET @Produces(MediaType.TEXT_PLAIN) public String getNamedStringWithParam(@DefaultValue("world") @QueryParam("name") String name) { return "Hello " + name; } Once again, the @Path annotation adds something to our URL, then the default value of the parameter is set in case there is no question mark and following it symbols in the URL using @DefaultValue annotation. In other words, if the parameter is omitted in the URL and it looks like http://localhost:8080/hello/query_param, a phrase “Hello world” is printed. The last annotation injects a parameter from the URL to the method's parameter. By the way, all these cases can be tested as was shown above. To test a method using query parameters one can use a queryParam(...) method of WebTarget interface. There is a couple of points to pay attention to. Firstly, there are other @*Param annotations available and secondly, the @DefaultValue annotation will not work with path parameters and to process the absence of the parameter a special sub-resource method should be introduced. You were patient enough to bear all this plain text staff, but it is not what REST APIs are about. Let's create another sub-resource method which is preprogrammed to return JSON representation. The first step is to create a representation class, which should be placed to com.javaeeeee.dwstart.core package. Let's limit ourselves to extremely simple example which is shown below. public class Greeting { @JsonProperty private String greeting; public Greeting() { } public Greeting(String greeting) { this.greeting = greeting; } public String getGreeting() { return greeting; } } The class above relies on one more important part of the Dropwizard stack namely Jackson , which can turn Java objects to JSON and vice versa. A @JsonProperty annotation is used to do the job. The sub-resource method looks like pretty much the same as our previously discussed methods. @Path("/hello_json") @GET @Produces(MediaType.APPLICATION_JSON) public Greeting getJSONGreeting() { return new Greeting("Hello world!"); } The difference is that we changed the media type and the method returns an instance of the greeting class. If you navigate your browser to to a URL http://localhost:8080/hello/hello_json or use cURL, you should see a JSON representation of the object {"greeting":"Hello world!"}. What if we remove the @Path annotation from the aforementioned method altogether? Well, if you try to access the localhost:8080/hello resource you'll see the text representation. How one could access the JSON-producing method? There is a special HTTP header called Accept which is used to instruct the server what representation to return, the process called content negotiation. The Jersey inside the Dropwizard will choose for us what method to use based on the content of the Accept header. Let's try cURL to do this. curl -w "\n" -H 'Accept: application/json' localhost:8080/hello/ The H-option is used to send headers and we instructed cURL to ask the JSON response. Other possible types to try could include text/plain and application/xml. The former should return the plain-text representation and the letter should result in error as there is no method in our resource class that can produce the latter media type response. Another way to engage in content negotiation is to use a REST client for your browser. There are several clients for each of major browsers but we will use Postman extension for Chrome browser. There are special fields to input headers as the screenshot below shows. One can enter the resource URL, headers and press Send button and the response will show up in the lower part of the window. To sum up we created a simple REST-like API using Dropwizard, which can greet its users. We learned how to create a Dropwizard project using Maven archetype and created a simple resource class to accomplish the task of greeting and a representation class to produce JSON response. An important ingredient of REST architecture style, HATEOAS, was omitted for now for simplicity reasons. Also a problem of testing resource classes was touched as well as the ways to access resources both from browser and command line. There are some other ideas for creating sub-resources such as returning the current date and adding two numbers using query parameters which can be easily implemented using the information presented in this article. References Dropwizard on GitHub Maven Archetypes Dropwizard Getting Started JAX-RS Resources and Subresources Dropwizard Testing Jersey Client API 2.x Jersey Client API 1.x Jackson annotations

Today I am going to discuss about creating a Grid in Android having image and associated checkbox. The idea is to have Grid with clickable images and checkbox. When an image is clicked the corresponding checkbox state is toggled. It is relatively easy to add custom items to the Grid. But its bit tricky to add clickable images and check/uncheck checkbox on click of the image. If you want to make the images clickable and check/uncheck the checkbox on image click, that is not that straightforward. In this article, I will take you through the creation of the Grid with clickable images and checkboxes. Creating a new project Open Eclipse and create a new android project. Choose a blank activity for the project. Create main Grid layout Open the layout file for the main activity and add a GridView component to it. Create Custom layout for grid items The next step is to create a custom layout that will be used to represent each item of the grid. Here we will define a custom layout using an ImageView and CheckBox android components. Create a new layout file named griditem.xml and add ImageView and CheckBox components to it as shown below: Adding Images to project For this sample project I am adding images to the project itself for use in the grid. But you can source those from database or any other content provider supported by android. In Android project there are few drawable-* folders under res folder. These are used for storing various resources used by the project. We can put images in any of these folders and Android SDK will copy them to other folders. If you have different images for different resolutions you can copy them to respective folders and correct image would be picked up based on the device resolution. Another option is to create a drawable folder under res and add images there. These will be copied to all drawable-* folders. We will use this approach here. Create custom adapter The next important step is to create a custom adapter which uses custom layout that we defined earlier to add items to the grid. The custom adapter should extend the BaseAdapter. The getView()method of the adapter is invoked for each item of the grid. In this method we assign values to the ImageView and checkbox. The listeners on the custom grid items are added here only. The code for getView() looks like the following: @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder holder; if (convertView == null) { holder = new ViewHolder(); convertView = mInflater.inflate( R.layout.griditems, null); holder.imageview = (ImageView) convertView.findViewById(R.id.grid_item_image); holder.checkbox = (CheckBox) convertView.findViewById(R.id.grid_item_checkbox); convertView.setTag(holder); } else { holder = (ViewHolder) convertView.getTag(); } holder.checkbox.setId(position); holder.imageview.setId(position); holder.checkbox.setOnClickListener(new OnClickListener() { public void onClick(View v) { CheckBox cb = (CheckBox) v; int id = cb.getId(); if (thumbnailsselection[id]){ //cb.setChecked(false); thumbnailsselection[id] = false; } else { //cb.setChecked(true); thumbnailsselection[id] = true; } } }); holder.imageview.setOnClickListener(new ImageClickListener(context, holder,thumbnailsselection)); holder.imageview.setImageResource(thumbnails[position]); holder.checkbox.setChecked(thumbnailsselection[position]); holder.id = position; return convertView; } Here we are saving the state of checkboxes in an array, thumbnailsselection. Since checkboxes are being added dynamically and there is no unique identifier for them, this will help in identifying the current state of checkbox whose state has to be toggled when an image is clicked. For the same reason we need to create a separate ImageClickListener. As we cannot identify the checkbox on click of corresponding image, we have to create the separate listener which holds the reference to holder class. Using this holder instance we can check/uncheck the checkbox when a corresponding image is clicked. Sometimes when you click on the image, the ImageClickListener is not invoked. The reason for this is that the checkbox overrides the focus event of container grid. Hence checkbox takes the focus when any item of the grid is clicked. To solve this issue you need to add the following properties to the checkbox. android:focusable=“false” android:focusableInTouchMode=“false” References Image icons source: http://www.iconarchive.com http://developer.android.com/

Recently I had a dispute with my colleagues regarding performance penalty of lazy vals in Scala. It resulted in a set of microbenchmarks which compare lazy and non-lazy vals performance. All the sources can be found at http://git.io/g3WMzA. But before going to the benchmark results let's try to understand what can cause the performance penalty. For my JMH benchmark I created a very simple Scala class with lazy val in it: @State(Scope.Benchmark) class LazyValCounterProvider { lazy val counter = SlowInitializer.createCounter() } Now let's take a look at what is hidden under the hood of lazy keyword. At first, we need to compile given code with scalac, and then it can be decompiled to correspondent Java code. For this sake I used JD decompiler. It produced the following code: @State(Scope.Benchmark) @ScalaSignature(bytes="...") public class LazyValCounterProvider { private SlowInitializer.Counter counter; private volatile boolean bitmap$0; private SlowInitializer.Counter counter$lzycompute() { synchronized (this) { if (!this.bitmap$0) { this.counter = SlowInitializer.createCounter(); this.bitmap$0 = true; } return this.counter; } } public SlowInitializer.Counter counter() { return this.bitmap$0 ? this.counter : counter$lzycompute(); } } As it's seen, the lazy keyword is translated to a classical double-checked locking idiom for delayed initialization. Thus, most of the time the only performance penalty may come from a single volatile read per lazy val read (except for the time it takes to initialize lazy val instance since its very first usage). Let's finally measure its impact in numbers. My JMH-based microbenchmark is as simple as: public class LazyValsBenchmarks { @Benchmark public long baseline(ValCounterProvider eagerProvider) { return eagerProvider.counter().incrementAndGet(); } @Benchmark public long lazyValCounter(LazyValCounterProvider provider) { return provider.counter().incrementAndGet(); } } A baseline method access a final counter object and increments an integer value by 1 by calling incrementAndGet . And as we've just found out, the main benchmark method - lazyValCounter - in addition to what baseline method does also does one volatile read. Note: all measurements are performed on MBA with Core i5 1.7GHz CPU. All results were obtained by running JMH in a throughput mode. Both score and score error columns show operations/second. Each JMH run made 10 iterations and took 50 seconds. I performed 6 measurements with the different JVM and JMH options: client VM, 1 thread Benchmark Score Score error baseline 412277751.619 8116731.382 lazyValCounter 352209296.485 6695318.185 client VM, 2 threads Benchmark Score Score error baseline 542605885.932 15340285.497 lazyValCounter 383013643.710 53639006.105 client VM, 4 threads Benchmark Score Score error baseline 551105008.767 5085834.663 lazyValCounter 394175424.898 3890422.327 server VM, 1 thread Benchmark Score Score error baseline 407010942.139 9004641.910 lazyValCounter 341478430.115 18183144.277 server VM, 2 threads Benchmark Score Score error baseline 531472448.578 22779859.685 lazyValCounter 428898429.124 24720626.198 server VM, 4 threads Benchmark Score Score error baseline 549568334.970 12690164.639 lazyValCounter 374460712.017 17742852.788 The numbers show that lazy vals performance penalty is quite small and can be ignored in practice. For further reading about the subject I would recommend SIP 20 - Improved Lazy Vals Initialization, which contains very interesting in-depth analysis of existing issues with lazy initialization implementation in Scala.

This article follows on from my Omnipresent, Infallible, Omnipotent and Instantaneous Build Technologies one a couple of day ago. Specifically the last section: “Minimalist test execution, via hacks”, that addressed test times being very lengthy. I’ve made a proof of concept of that for Maven. The tests impacted by a change (a pending change specifically) can now be quickly determined and fed into the test runner to massively reduce test times. Massively reduced, this is, if you’ve managed to engineer hours of Selenium tests. Proof of concept I forked a Github project that Petri Kainulainen had made to discuss coverage for a Maven projects. Clone my fork, but cd into the “code-coverage-jacoco” directory. Running testimpact.sh there – it will rebuild a map of what tests cover what production-classes (sources). I’ve checked in the previous results from running this script, that’s what a team would do. It runs Maven against one test at a time, to calculate coverage then store that per test. Actually for Petri’s example, I’m only focussing on the integration tests (run by the “failsafe” plugin) rather than the unit tests (run by the “surefire” plugin). Even though Petri’s example project is not launching Selenium (or equivalent slow test), the integration test phase is where you would run that for a canonical Maven project. The testimpact.sh script uses python and ack (you’ll have to install those if you want to run this). I tried to use sqlite3’s CSV ingesting, but it was impossibly opaque, even with using StackOverflow’s best Questions/Answers, so I flipped to Python. Petri’s example uses JaCoCo for coverage, which spits out a handy CSV report (as well as HTML). There are some text files in src/integration-test/meta/ccexample that show the sources covered by each test. Yes, they are checked in. Those files end in .java but are actually plain text (sorry): There’s another file src/integration-test/impact-map.txt that contains a list of production sources and the tests that would exercise them. Actually its a map of sources vs tests: Experimenting with what I’ve done Change one of the two production classes in src/main/java/ccexample. Yes they are clones of each other – that’s just something I did after forking to increase the class count at the start. Don’t commit that pending change, just leave it there showing up as modified in git status. Run python tests.py and watch it run one or two tests in the same invocation. Now undo that change, and change the other source file, and run python tests.py again. Different tests ran, right? Undo that change, and do python tests.py once more. No tests ran, right? That would be the same for changed sources/classes that had no tests exercising them (covering them under test invocation) at all. Of course these few tests are really quick, but they could have been three subset from hundreds or thousands of tests with an elapsed time of many hours. Turning the idea into a solution It is also worth noting that scripts as I have them are not robust or optimized. There’s more source-control systems than just Git, of course. The script needs to be able to work for a commit too, not just a pending commit. The storage format for impact-map.txt will not scale, and you might want to excise certain categories of POJO if every test exercises them. To be correct in Maven-land, this should be a bunch of plugins that fit the Maven style. One plugin would be invoked from Jenkins and would probably run constantly if corresponding test times are up in the hours. That Jenkins job should check in changes to the meta-files as it sees changes. This is benign, and useful to team members who may want the shorter build. Would you check the impact map into source-control? It seems to me that the map data is related to the other source files. Perhaps if you took a historical view to things, the impact maps change with the source code at the same time. If you were bug-fixing something from the past (checking out a prior revision), you might be happy that the impact map also goes back in time. Of course there’s nothing here that couldn’t be stored in a key/value store, including the changing map over time. Or a service that could answer the question “what tests should I run if these source files are changed?” Except perhaps that uncommitted work (on your own workstation) isn’t going to be present in that store until after a commit, and the impact map data us updated to that into account. Taking the idea even further I’ve suggested that Selenium is the technology that would greatly lengthen test times. There are many other test technologies that are one, two or three orders slower than perfect unit tests. This idea is applicable to much more than just Selenium – the only requirement is to be able to measure coverage while individual tests are running. What I have done could also be extended to the “surefire” phase – almost identical to what I’ve done already – an opportunity for reuse of course. CI daemons like Jenkins could benefit from the same impact-driven test time reduction. At least the per-commit jobs that we do for the Continuous Delivery era of enterprise development. This idea could be extended to the test-method level. That would be harder still, but achievable in the same way. It comes with arguably negligible gains, though. You’d code it all, and work out that 5% wasn’t worth it (versus other ways of speeding up tests). We’d need Intellij and Eclipse plugins for this. The script needs to be able to work for range of commits as many teams batch them in in Jenkins-land. I wonder what is out there that already does this sort of thing already. Followups (Jan 13, 17, 2015) Markus Kohler notes: This is a great idea and I guess similar to what Google does (there was blog post about it, can’t find it ATM). But I think as it is it would not be completely correct. The reason is that as far as I can see, you just run the tests that use the modified class files. That is not enough, because in Java changing one source code file might result in other files needed to be recompiled. Gradle’s Java plugin (http://www.gradle.org/docs/current/userguide/java_plugin.html) computes that set of files for example for incremental compilation. As an example if a final static String is changed and that String is used in other classes, these classes has to be recompiled because the Java compiler inlines these kind of strings. Any Test that uses these classes would have to be re-run. He’s quite right there’s room for some edge case mistakes. To overcome those, you would need to check for changes that would lead to final static fields being inlined into other classes. Maybe a list of source files that, if changed, would cause all tests to be re-run (after a suitable warning).