This is a sequel to my blog post on "A Client Server File Sharing Application in C#" I have received several emails asking for the application to be made into a whole package instead of having it as a separate client and server applications. In order to save time and not to send the solution as email to people again, I have decided to make it a blog post and make the whole package available. The application is written in C# and it will allow files to be sent from one computer to another on the network. It attempts to compile what both the client and server applications in my previous post- A Client Server File Sharing Application in C# do into a single project. To gain a full understanding of the workings, I recommend you read the following- The full listing of the source code is below. using System;; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.IO; using System.Linq; using System.Net; using System.Net.NetworkInformation; using System.Net.Sockets; using System.Text; using System.Threading.Tasks; using System.Windows.Forms; namespace FileSharingApp { public partial class Form1 : Form { private static string shortFileName = ""; private static string fileName = ""; public delegate void FileRecievedEventHandler(object source, string fileName); public event FileRecievedEventHandler NewFileRecieved; public Form1() { InitializeComponent(); } private void Form1_Load(object sender, EventArgs e) { this.NewFileRecieved+=new FileRecievedEventHandler (Form1_NewFileRecieved); } private void Form1_NewFileRecieved(object sender, string fileName) { this.BeginInvoke( new Action( delegate() { MessageBox.Show("New File Recieved\n"+fileName); System.Diagnostics.Process.Start("explorer", @"c:\"); })); } private void btnListen_Click(object sender, EventArgs e) { int port = int.Parse(txtHost.Text); Task.Factory.StartNew(() => HandleIncomingFile(port)); MessageBox.Show("Listening on port"+port); } public void HandleIncomingFile(int port) { try { TcpListener tcpListener = new TcpListener(port); tcpListener.Start(); while (true) { Socket handlerSocket = tcpListener.AcceptSocket(); if (handlerSocket.Connected) { string fileName = string.Empty; NetworkStream networkStream = new NetworkStream (handlerSocket); int thisRead = 0; int blockSize = 1024; Byte[] dataByte = new Byte[blockSize]; lock (this) { string folderPath = @"c:\"; handlerSocket.Receive(dataByte); int fileNameLen = BitConverter.ToInt32(dataByte, 0); fileName = Encoding.ASCII.GetString(dataByte, 4, fileNameLen); Stream fileStream = File.OpenWrite(folderPath + fileName); fileStream.Write(dataByte, 4+fileNameLen,( 1024-(4+fileNameLen))); while (true) { thisRead = networkStream.Read(dataByte, 0, blockSize); fileStream.Write(dataByte, 0,thisRead); if (thisRead == 0) break; } fileStream.Close(); } if (NewFileRecieved != null) { NewFileRecieved(this, fileName); } handlerSocket = null; } } } catch { } } private void btnBrowse_Click(object sender, EventArgs e) { OpenFileDialog dlg = new OpenFileDialog(); dlg.Title = "File Sharing Client"; dlg.ShowDialog(); txtFile.Text = dlg.FileName; fileName = dlg.FileName; shortFileName = dlg.SafeFileName; } private void btnSend_Click(object sender, EventArgs e) { string ipAddress = txtIPAddress.Text; int port = int.Parse(txtPort.Text); string fileName = txtFile.Text; Task.Factory.StartNew(() => SendFile(ipAddress,port, fileName,shortFileName)); MessageBox.Show("File Sent"); } public void SendFile(string remoteHostIP, int remoteHostPort , string longFileName, string shortFileName) { try { if(!string.IsNullOrEmpty(remoteHostIP)) { byte[] fileNameByte = Encoding.ASCII.GetBytes (shortFileName); byte[] fileData = File.ReadAllBytes(longFileName); byte[] clientData = new byte[4 + fileNameByte.Length + fileData.Length]; byte[] fileNameLen = BitConverter.GetBytes( fileNameByte.Length); fileNameLen.CopyTo(clientData, 0); fileNameByte.CopyTo(clientData,4); fileData.CopyTo(clientData, 4 + fileNameByte.Length); TcpClient clientSocket = new TcpClient(remoteHostIP, remoteHostPort); NetworkStream networkStream = clientSocket.GetStream(); networkStream.Write(clientData, 0, clientData.GetLength (0)); networkStream.Close(); } } catch { } } } } The Complete source code of the application is available for download Here

I often use IntelliJ to run applications, and on occasion things go wrong. For example, a thread that wont terminate can cause a running application to become unstoppable via the IntelliJ UI. Usually when this happens I end up running ps aux | grep java and following up with a kill -9 for each process that looks like it might be the one I'm looking for. On good days there's only a few processes; however, things are more complicated when I have several to look through. Last week I noticed that the command used to launch the process printed in the Console window, and, more importantly, the idea.launcher.port is part of that command: e.g. idea.launcher.port=7538. Assuming the port is unique, or even almost unique it's much easier to ps aux | grep for than java.

infographic: clouds computing and history i have prepared three new infographics for you;aall of them related with cloud computing. these infographics will tell you about history of cloud computing, its definition, and who needs this cloud. i think that this will be interesting for you. information graphics (known as infographics) are one of the best ways to transfer some information into a reader’s mind. it can be something new, or other useful information gathered in one place. nowadays many people don’t have enough time to read a lot of text on multiple screens. infographics makes the information intuitive and understandable. that’s why we would like to share the best relevant infographics from all over the web. original source: cloud computing by the small business authority original source: a complete history of cloud computing original source: hosting decisions, from the chalkboard

I.T. is full of complex things that should (and sometimes could) be simple. Getting the JQPL/SQL String representation for a JPA 2.0 CriteriaQuery is one of them. By now you all know the JPA 2.0 Criteria API : a type safe way to write a JQPL query. This API is clever in the way that you don’t use Strings to build your query, but is quite verbose… and sometimes you get lost in dozens of lines of Java code, just to write a simple query. You get lost in your CriteriaQuery, you don’t know why your query doesn’t work, and you would love to debug it. But how do you debug it ? Well, one way would be by just displaying the JPQL and/or SQL representation. Simple, isn’t it ? Yes, but JPA 2.0 javax.persistence.Query doesn’t have an API to do this. You then need to rely on the implementation… meaning, the code is different if you use EclipseLink, Hibernate or OpenJPA. The CriteriaQuery we want to debug Let’s say you have a simple Book entity and you want to retrieve all the books sorted by their id. Something like SELECT b FROM Book b ORDER BY b.id DESC. How would you write this with the CriteriaQuery ? Well, something like these 5 lines of Java code : CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery q = cb.createQuery(Book.class); Root b = q.from(Book.class); q.select(b).orderBy(cb.desc(b.get("id"))); TypedQuery findAllBooks = em.createQuery(q); So imagine when you have more complex ones. Sometimes, you just get lost, it gets buggy and you would appreciate to have the JPQL and/or SQL String representation to find out what’s happening. You could then even unit test it. Getting the JPQL/SQL String Representations for a Criteria Query So let’s use an API to get the JPQL/SQL String representations of a CriteriaQuery (to be more precise, the TypedQuery created from a CriteriaQuery). The bad news is that there is no standard JPA 2.0 API to do this. You need to use the implementation API hoping the implementation allows it (thank god that’s (nearly) the case for the 3 main JPA ORM frameworks). The good news is that the Query interface (and therefore TypedQuery) has an unwrap method. This method returns the provider’s query API implementation. Let’s see how you can use it with EclipseLink, Hibernate and OpenJPA. EclipseLink EclipseLink‘s Query representation is the org.eclipse.persistence.jpa.JpaQuery interface and the org.eclipse.persistence.internal.jpa.EJBQueryImpl implementation. This interface gives you the wrapped native query (org.eclipse.persistence.queries.DatabaseQuery) with two very handy methods : getJPQLString() and getSQLString(). Unfortunatelly the getJPQLString() method will not translate a CriteriaQuery into JPQL, it only works for queries originally written in JPQL (dynamic or named query). The getSQLString() method relies on the query being “prepared”, meaning you have to run the query once before getting the SQL String representation. findAllBooks.unwrap(JpaQuery.class).getDatabaseQuery().getJPQLString(); // doesn't work for CriteriaQuery findAllBooks.unwrap(JpaQuery.class).getDatabaseQuery().getSQLString(); Hibernate Hibernate‘s Query representation is org.hibernate.Query. This interface has several implementations and the very useful method that returns the SQL query string : getQueryString(). I couldn’t find a method that returns the JPQL representation, if I’ve missed something, please let me know. findAllBooks.unwrap(org.hibernate.Query.class).getQueryString() OpenJPA OpenJPA‘s Query representation is org.apache.openjpa.persistence.QueryImpl and also has a getQueryString() method that returns the SQL (not the JPQL). It delegates the call to the internal org.apache.openjpa.kernel.Query interface. I couldn’t find a method that returns the JPQL representation, if I’ve missed something, please let me know. findAllBooks.unwrap(org.apache.openjpa.persistence.QueryImpl.class).getQueryString() Unit testing Once you get your SQL String, why not unit test it ? Hey, but I don’t want to test my ORM, why would I do that ? Well, it happens that I’ve discovered a but in the new releases of OpenJPA by unit testing a query… so, there is a use case for that. Anyway, this is how you could do it : assertEquals("SELECT b FROM Book b ORDER BY b.id DESC", findAllBooksCriteriaQuery.unwrap(org.apache.openjpa.persistence.QueryImpl.class).getQueryString()); Conclusion As you can see, it’s not that simple to get a String representation for a TypedQuery. Here is a digest of the three main ORMs : ORM Framework Query implementation How to get the JPQL String How to get the SPQL String EclipseLink JpaQuery getDatabaseQuery().getJPQLString()* getDatabaseQuery().getSQLString()** Hibernate Query N/A getQueryString() OpenJPA QueryImpl getQueryString() N/A (*) Only possible on a dynamic or named query. Not possible on a CriteriaQuery (**) You need to execute the query first, if not, the value is null To illustrate all that I’ve written simple test cases using EclipseLink, Hibernate and OpenJPA that you can download from GitHub. Give it a try and let me know. And what about having an API in JPA 2.1 ? For a developers’ point of view it would be great to have two methods in the javax.persistence.Query (and therefore javax.persistence.TypedQuery) interface that would be able to easily return the JPQL and SQL String representations, e.g : Query.getJPQLString() and Query.getSQLString(). Hey, that would be the perfect time to have it in JPA 2.1 that will be shipped in less than a year. Now, as an implementer, this might be tricky to do, I would love to ear your point of view on this. Anyway, I’m going to post an email to the JPA 2.1 Expert Group… just in case we can have this in the next version of JPA ;o) References http://efreedom.com/Question/1-6412774/Get-SQL-String-JPQLQuery http://old.nabble.com/Cannot-get-the-JPQL—SQL-String-of-a-CriteriaQuery-td33882629.html http://paddyweblog.blogspot.fr/2010/04/some-examples-of-criteria-api-jpa-20.html http://www.altuure.com/2010/09/23/jpa-criteria-api-by-samples-part-i/ http://www.altuure.com/2010/09/23/jpa-criteria-api-by-samples-%E2%80%93-part-ii/ http://www.jumpingbean.co.za/blogs/jpa2-criteria-api http://wiki.eclipse.org/EclipseLink/FAQ/JPA#How_to_get_the_SQL_for_a_Query.3F

In how many ways can you retrieve TeamCity artifacts? I say plenty to choose from! If you’re in a world of Java build tools then you can use plain HTTP request, Ant + Ivy, Gradle and Maven to download and use binaries produced by TeamCity build configurations. How? Read on. Build Configuration “id” Before you retrieve artifacts of any build configuration you need to know its "id" which can be seen in a browser when corresponding configuration is browsed. Let’s take IntelliJ IDEA Community Edition project hosted at teamcity.jetbrains.com as an example. Its “Community Dist” build configuration provides a number of artifacts which we’re going to play with. And as can be seen on the screenshot below, its "id" is "bt343". HTTP Anonymous HTTP access is probably the easiest way to fetch TeamCity artifacts, the URL to do so is: http://server/guestAuth/repository/download/// Fot this request to work 3 parameters need to be specified: btN Build configuration "id", as mentioned above. buildNumber Build number or one of predefined constants: "lastSuccessful", "lastPinned", or "lastFinished". For example, you can download periodic IDEA builds from last successful TeamCity execution. artifactName Name of artifact like "ideaIC-118.SNAPSHOT.win.zip". Can also take a form of "artifactName!archivePath" for reading archive’s content, like IDEA’s build file. You can get a list of all artifacts produced in a certain build by requesting a special "teamcity-ivy.xml" artifact generated by TeamCity. Ant + Ivy All artifacts published to TeamCity are accompanied by "teamcity-ivy.xml" Ivy descriptor, effectively making TeamCity an Ivy repository. The code below downloads "core/annotations.jar" from IDEA distribution to "download/ivy" directory: "ivyconf.xml" "ivy.xml" "build.xml" Gradle Identically to Ivy example above it is fairly easy to retrieve TeamCity artifacts with Gradle due to its built-in Ivy support. In addition to downloading the same jar file to "download/gradle" directory with a custom Gradle task let’s use it as "compile" dependency for our Java class, importing IDEA’s @NotNull annotation: "Test.java" import org.jetbrains.annotations.NotNull; public class Test { private final String data; public Test ( @NotNull String data ){ this.data = data; } } "build.gradle" apply plugin: 'java' repositories { ivy { ivyPattern 'http://teamcity.jetbrains.com/guestAuth/repository/download/[module]/[revision]/teamcity-ivy.xml' artifactPattern 'http://teamcity.jetbrains.com/guestAuth/repository/download/[module]/[revision]/[artifact](.[ext])' } } dependencies { compile ( 'org:bt343:lastSuccessful' ){ artifact { name = 'core/annotations' type = 'jar' } } } task copyJar( type: Copy ) { from configurations.compile into "${ project.projectDir }/download/gradle" } Maven The best way to use Maven with TeamCity is by setting up an Artifactory repository manager and its TeamCity plugin. This way artifacts produced by your builds are nicely deployed to Artifactory and can be served from there as from any other remote Maven repository. However, you can still use TeamCity artifacts in Maven without any additional setups. "ivy-maven-plugin" bridges two worlds allowing you to plug Ivy resolvers into Maven’s runtime environment, download dependencies required and add them to corresponding "compile" or "test" scopes. Let’s compile the same Java source from the Gradle example but using Maven this time. "pom.xml" 4.0.0 com.test maven jar 0.1-SNAPSHOT [${project.groupId}:${project.artifactId}:${project.version}] Ivy Maven plugin example com.github.goldin ivy-maven-plugin 0.2.5 get-ivy-artifacts ivy initialize ${project.basedir}/ivyconf.xml ${project.basedir}/ivy.xml ${project.basedir}/download/maven compile When this plugin runs it resolves IDEA annotations artifact using the same "ivyconf.xml" and "ivy.xml" files we’ve seen previously, copies it to "download/maven" directory and adds to "compile" scope so our Java sources can compile. GitHub Project All examples demonstrated are available in my GitHub project. Feel free to clone and run it: git clone git://github.com/evgeny-goldin/teamcity-download-examples.git cd teamcity-download-examples chmod +x run.sh dist/ant/bin/ant gradlew dist/maven/bin/mvn ./run.sh Resources The links below can provide you with more details: TeamCity – Patterns For Accessing Build Artifacts TeamCity – Accessing Server by HTTP TeamCity – Configuring Artifact Dependencies Using Ant Build Script Gradle – Ivy repositories "ivy-maven-plugin" That’s it, you’ve seen it – TeamCity artifacts are perfectly accessible using either of 4 ways: direct HTTP access, Ant + Ivy, Gradle or Maven. Which one do you use? Let me know!

with the release of ios 5, fixed positioned layout is said to be supported in mobilesafari. the word supported needs to be taken with a pinch of salt, because there’s all kinds of issues which i intend to show you in the following post. note that i have filed bugs for a number of these during the beta of ios 5 – but god knows how the radar apple thing works, so i don’t know the issue numbers. update: i’ve added “scrolling == unusable position:fixed element” based on corey duston pointing out more bugs with position fixed. position:fixed, who cares? i might have argued that fixed positioned doesn’t matter or isn’t really required in a good app. however, there’s an increasing number of ios apps i’ve noticed that are actually just a collection of webviews (mini-mobilesafaris) with fixed position toolbars as seen in apple’s own appstore app, the native facebook app and instagram below: appstore via @devongovett , facebook via @9eggs issues i’ve created a number of example pages that you can view for yourself, which are used in the following videos. juddering if you add position : fixed in any normal way as you might on a “desktop” site, you’ll see some degree of juddering as the page scrolls. note that this is the simulator running, but i’ve also captured the real iphone (using reflection) showing the same behaviour. the page used was: jsbin.com/3/ixewok/6/ ( edit ) no updated values on scroll the sharp eyed viewer might have spotted some values changing in the video. i’m monitoring the window . scrolltop and window . pageyoffset (and another value which we’ll look at later). you’ll notice that the values don’t change until the scroll has finished. this is a problem if you want to monitor the page position to simulate effects like the bumping and shunting of category headings like you might see in the address book app. position drift if the page is zoomed at all, which you can get in ios when the user rotates from portrait to landscape, as the user scrolls in any scale beyond 1 (i.e. zoomed), the position fixed element drifts upwards (i’ve seen this drift entirely out of view before in other sites): the page used was: jsbin.com/3/ixewok/6/ ( edit ) focus jumping if there’s a focusable element inside the position fixed element, i.e. an input element, this can cause the entire fixed element to jump out of place. this will only happen if the user has scrolled any amount (but if you’re using position : fixed you’re expecting exactly that kind of usage). the page used was: jsbin.com/3/ixewok/8/ ( edit ) scrolling == unusable position:fixed element corey dutson pointed out there’s another issue with position fixed. although his example show scrolling using javascript, the core problem is: if the page moves programatically (i.e. the user didn’t cause the scroll) the elements inside the fix element are unavailable. from the screencast i’ve recorded you can see using iwebinspector that although mobilesafari has painted the fixed element in place, it’s actually not there – the actual element remains in place until you touch and move the page again. the page used was: jsbin.com/3/ixewok/13/ ( edit ) i don’t have a fix for this yet, and i suspect it’s a core painting issue inside of mobilesafari – but i will keep playing to see if there’s something that can be done. fixing juddering with ios 5, mobilesafari also came with - webkit - overflow - scrolling : touch . this is actually intended for inline blocks of content to the page (i mean inline with respect to the document). if i change the css in my previous example, and set the height of my html , body and content block to 100%, then apply the scrolling touch property to the content, the juddering goes away. however, that alone does not fix the juddering. the trick would seem to be: make sure your fixed position element is not on a “moving canvas”. this example has the fixed element over a scrolling element, but not inside of it. so when i tried to apply this technique to the body element, the juddering was still visible, as the fixed element was inside the scrolling element. i also captured this on the real device too. the page used was: jsbin.com/3/ixewok/10/ ( edit ) getting scroll position to update again, those keen eyes might have spotted values are moving again. note that as i’ve changed the css the body is no longer scrolling, so the 0 values on the left and right are window . scrolltop and window . pageyoffset respectively. since the window isn’t scrolling, the content block is in an overflow, the values won’t change. however, the content . scrollx value is changing – but it doesn’t by default. firstly, you have to attach any touch event handler to get this value to update as the user is scrolling (or actually touching), so in javascript i can add: content.ontouchstart = function () {}; the touch event will work with start, end and move, and just needs a value set (note that i didn’t test just setting it to true – that might work too!). however, it’s still not perfect. you’ll see from the video above, that it only updated whilst i’m touching . as soon as i let go during a swipe to scroll, the momentum makes the page continue to scroll, but the value doesn’t update. i’ve yet to work out if it’s even possible to capture this value. ::sigh:: to conclude / tl;dr don’t use position : fixed inside a scrolling element, it’s juddery and looks rubbish (i’ve seen much worse than the juddering shown in the videos). do make use of - webkit - overflow - scrolling : touch and if you want the scroll values, make sure you attach a touch handler to that scrolling element. at the same time: make this work in other mobile browsers too – don’t just cater to apple. it’s a huge headache that apple have half arsed-ed-ly fixed the position : fixed issue and done in a typically microsoft proprietory way.

Sort Linked List in Ascending Order - C# Efficiency: O(n^2) Inspired by Selection Sort algorithm /// /// This method sorts elements in linked list and returns a new sorted linked list /// /// head node of unsorted linked list /// number of elements in unsorted linked list /// head node of new sorted linked list public static Node SortLinkedList(Node head, int count) { // Basic Algorithm Steps //1. Find Min Node //2. Remove Min Node and attach it to new Sorted linked list //3. Repeat "count" number of times Node _current = head; Node _previous = _current; Node _min = _current; Node _minPrevious = _min; Node _sortedListHead = null; Node _sortedListTail = _sortedListHead; for (int i = 0; i < count; i++) { _current = head; _min = _current; _minPrevious = _min; //Find min Node while (_current != null) { if (_current.Data < _min.Data) { _min = _current; _minPrevious = _previous; } _previous = _current; _current = _current.Next; } // Remove min Node if (_min == head) { head = head.Next; } else if (_min.Next == null) //if tail is min node { _minPrevious.Next = null; } else { _minPrevious.Next = _minPrevious.Next.Next; } //Attach min Node to the new sorted linked list if (_sortedListHead != null) { _sortedListTail.Next = _min; _sortedListTail = _sortedListTail.Next; } else { _sortedListHead = _min; _sortedListTail = _sortedListHead; } } return _sortedListHead; }

I really like Spring, so I tend to use its features to the fullest. However, in some dark corners of its philosophy, I tend to disagree with some of its assumptions. One such assumption is the way database testing should work. In this article, I will explain how to configure your projects to make Spring Test and DBUnit play nice together in a multi-developers environment. Context My basic need is to be able to test some complex queries: before integration tests, I've to validate those queries get me the right results. These are not unit tests per se but let's assilimate them as such. In order to achieve this, I use since a while a framework named DBUnit. Although not maintained since late 2010, I haven't found yet a replacement (be my guest for proposals). I also have some constraints: I want to use TestNG for all my test classes, so that new developers wouldn't think about which test framework to use I want to be able to use Spring Test, so that I can inject my test dependencies directly into the test class I want to be able to see for myself the database state at the end of any of my test, so that if something goes wrong, I can execute my own queries to discover why I want every developer to have its own isolated database instance/schema Considering the last point, our organization let us benefit from a single Oracle schema per developer for those "unit-tests". Basic set up Spring provides the AbstractTestNGSpringContextTests class out-of-the-box. In turn, this means we can apply TestNG annotations as well as @Autowired on children classes. It also means we have access to the underlying applicationContext, but I prefer not to (and don't need to in any case). The structure of such a test would look like this: @ContextConfiguration(location = "classpath:persistence-beans.xml") public class MyDaoTest extends AbstractTestNGSpringContextTests { @Autowired private MyDao myDao; @Test public void whenXYZThenTUV() { ... } } Readers familiar with Spring and TestNG shouldn't be surprised here. Bringing in DBunit DbUnit is a JUnit extension targeted at database-driven projects that, among other things, puts your database into a known state between test runs. [...] DbUnit has the ability to export and import your database data to and from XML datasets. Since version 2.0, DbUnit can also work with very large datasets when used in streaming mode. DbUnit can also help you to verify that your database data match an expected set of values. DBunit being a JUnit extension, it's expected to extend the provided parent class org.dbunit.DBTestCase. In my context, I have to redefine some setup and teardown operation to use Spring inheritance hierarchy. Luckily, DBUnit developers thought about that and offer relevant documentation. Among the different strategies available, my tastes tend toward the CLEAN_INSERT and NONE operations respectively on setup and teardown. This way, I can check the database state directly if my test fails. This updates my test class like so: @ContextConfiguration(locations = {"classpath:persistence-beans.xml", "classpath:test-beans.xml"}) public class MyDaoTest extends AbstractTestNGSpringContextTests { @Autowired private MyDao myDao; @Autowired private IDatabaseTester databaseTester; @BeforeMethod protected void setUp() throws Exception { // Get the XML and set it on the databaseTester // Optional: get the DTD and set it on the databaseTester databaseTester.setSetUpOperation(DatabaseOperation.CLEAN_INSERT); databaseTester.setTearDownOperation(DatabaseOperation.NONE); databaseTester.onSetup(); } @Test public void whenXYZThenTUV() { ... } } Per-user configuration with Spring Of course, we need to have a specific Spring configuration file to inject the databaseTester. As an example, here is one: However, there's more than meets the eye. Notice the databaseTester has to be fed a datasource. Since a requirement is to have a database per developer, there are basically two options: either use a in-memory database or use the same database as in production and provide one such database schema per developer. I tend toward the latter solution (when possible) since it tends to decrease differences between the testing environment and the production environment. Thus, in order for each developer to use its own schema, I use Spring's ability to replace Java system properties at runtime: each developer is characterized by a different user.name. Then, I configure a PlaceholderConfigurer that looks for {user.name}.database.properties file, that will look like so: db.username=myusername1 db.password=mypassword1 db.schema=myschema1 This let me achieve my goal of each developer using its own instance of Oracle. If you want to use this strategy, do not forget to provide a specific database.properties for the Continuous Integration server. Huh oh? Finally, the whole testing chain is configured up to the database tier. Yet, when the previous test is run, everything is fine (or not), but when checking the database, it looks untouched. Strangely enough, if you did load some XML dataset and assert it during the test, it does behaves accordingly: this bears all symptoms of a transaction issue. In fact, when you closely look at Spring's documentation, everything becomes clear. Spring's vision is that the database should be left untouched by running tests, in complete contradiction to DBUnit's. It's achieved by simply rollbacking all changes at the end of the test by default. In order to change this behavior, the only thing to do is annotate the test class with @TransactionConfiguration(defaultRollback=false). Note this doesn't prevent us from specifying specific methods that shouldn't affect the database state on a case-by-case basis with the @Rollback annotation. The test class becomes: @ContextConfiguration(locations = {classpath:persistence-beans.xml", "classpath:test-beans.xml"}) @TransactionConfiguration(defaultRollback=false) public class MyDaoTest extends AbstractTestNGSpringContextTests { @Autowired private MyDao myDao; @Autowired private IDatabaseTester databaseTester; @BeforeMethod protected void setUp() throws Exception { // Get the XML and set it on the databaseTester // Optional: get the DTD and set it on the databaseTester databaseTester.setSetUpOperation(DatabaseOperation.CLEAN_INSERT); databaseTester.setTearDownOperation(DatabaseOperation.NONE); databaseTester.onSetup(); } @Test public void whenXYZThenTUV() { ... } } Conclusion Though Spring and DBUnit views on database testing are opposed, Spring's configuration versatility let us make it fit our needs (and benefits from DI). Of course, other improvements are possible: pushing up common code in a parent test class, etc. To go further: Spring Test documentation DBUnit site Database data verification Database testing best practices Generating DTD from your database schema

Dynamic and static properties are really interesting. Learn about managing dynamic property in Spring.

A Robust Splitter Aggregator Design Strategy - Messaging Gateway Adapter Pattern What do we mean by robust? In the context of this article, robustness refers to an ability to manage exception conditions within a flow without immediately returning to the caller. In some processing scenarios n of m responses is good enough to proceed to conclusion. Example processing scenarios that typically have these tendencies are: Quotations for finance, insurance and booking systems. Fan-out publishing systems. Why do we need Robust Splitter Aggregator Designs? First and foremost an introduction to a typical Splitter Aggregator pattern maybe necessary. The Splitter is an EIP pattern that describes a mechanism for breaking composite messages into parts in order that they can be processed individually. A Router is an EIP pattern that describes routing messages into channels - aiming them at specific messaging endpoints. The Aggregator is an EIP pattern that collates and stores a set of messages that belong to a group, and releases them when that group is complete. Together, those three EIP constructs form a powerful mechanism for dividing processing into distinct units of work. Spring Integration (SI) uses the same pattern terminology as EIP and so readers of that methodology will be quite comfortable with Spring Integration Framework constructs. The SI Framework allows significant customisations of all three of those constructs and furthermore, by simply using asynchronous channels as you would in any other multi-threaded configuration, allows those units of work to be executed in parallel. An interesting challenge working with SI Splitter Aggregator designs is building appropriately robust flows that operate predictably in a number of invocation scenarios. A simple splitter aggregator design can be used in many circumstances and operate without heavy customisation of the SI constructs. However, some service requirements demand a more robust processing strategy and therefore more complex configuration. The following sections describe and show what a Simple Splitter Aggregator design actually looks like, the type of processing your design must be able to deal with and then goes on to suggest candidate solutions for more robust processing. A Simple Splitter Aggregator Design The following Splitter Aggregator design shows a simple flow that receives document request messages into messaging gateway, splits the message into two processing routes and then aggregates the response. Note that the diagram has been built from EIP constructs in OmniGraffle rather than being an Integration Graph view from within STS; the channels are missing from the diagram for the sake of brevity. SI Constructs in detail: Messaging Gateways - there are three messaging gateways. A number of configurations are available for gateway specifications but significantly can return business objects, exceptions and nulls (following a timeout). The gateway to the far left is the service gateway for which we are defining the flow. The other two gateways, between the Router and Aggregator, are external systems that will be providing responses to business questions that our flow generates. The Splitter - a single splitter exists and is responsible for consuming the document message and producing a collection of messages for onward processing. The Java signature for the, most often, custom Splitter specifies a single object argument and a collection for return. The Recipient List Router - a single router exists, any appropriate router can be used, chose the one that closely matches your requirements - you can easily route by expression or payload type. The primary purpose of the router is route a collection of messages supplied by the splitter. This is a pretty typical Splitter Aggregator configuration. Aggregator - a single construct that is responsible for collecting messages together in a group in order that further processing can take place on the gateway responses. Although the Aggregator can be configured with attributes and bean definitions to provide alternative grouping and release strategies, most often the default aggregation strategy suffices. Interesting Aspects of Splitter Aggregator Operation Gateway - the inbound gateway, the one on the far left, may or may not have an error handling bean reference defined on it. If it does then that bean will have an opportunity to handle an exceptions thrown within the flow to the right of that gateway. If not, any exception will be thrown straight out of the gateway. Gateway - an optional default-reply-timeout can be set on each of the gateways, there are significant implications for setting this value, ensure that they're well understood. An expired timeout will result in a null being returned from the gateway. This is the very same condition that can lead to a thread getting parked if an upstream gateway also has no default-reply-timeout set. Splitter Input Channel - this can be a simple direct channel or a direct channel with a dispatcher defined on it. If the channel has a dispatcher specified the flow downstream of this point will be asynchronous, multi-threaded. This also changes the upstream gateway semantics as it usually means that an otherwise impotent default-reply-timeout becomes active. Splitter - the splitter must return a single object. The single object returned by the splitter is a collection, a java.util.List. The SI framework will take each member of that list and feed it into the output-channel of the Splitter - as with this example, usually straight into a router. The contract for Splitter List returns is as its use in Java - it may contain zero, one or more elements. If the splitter returns an empty list it's unlikely that the router will have any work to do and so the flow invocation will be complete. However, if the List contains one item, the SI framework will extract that item from the list and push it into the router, if this gets routed successfully, the flow will continue. Router - the router will simply route messages into one of two gateways in this example. Gateways - the two gateways that are used between the Splitter and Aggregator are interesting. In this example I have used the generic gateway EIP pattern to represent a message sub-system but not defined it explicitly - we could use an HTTP outbound gateway, another SI flow or any other external system. Of course, for each of those sub-systems, a number of responses is possible. Depending on the protocol and external system, the message request may fail to send, the response fail to arrive, a long running process invoked, a network error or timeout or a general processing exception. Aggregator - the single aggregator will wait for a number of responses depending on what's been created by the Splitter. In the case where the splitter return list is empty the Aggregator will not get invoked. In the case where the Splitter return list has one entry, the aggregator will be waiting for one gateway response to complete the group. In the case where the Splitter list has n entries the Aggregator will be waiting for n entries to complete the group. Custom correlation strategies, release strategies and message stores can be injected amongst a set of rich configuration aspects. Interesting Aspects of Simple Splitter Aggregator Operation The primary deciding factor for establishing whether this type of simple gateway is adequate for requirements is to understand what happens in the event of failure. If any exception occurring in your SI flow results in the flow invocation being abandoned and that suits your requirements, there's no need to read any further. If, however, you need to continue processing following failure in one of the gateways the remainder of this article may be of more interest. Exceptions, from any source, generated between the splitter and aggregator, will result in an empty or partial group being discarded by the Aggregator. The exception will propagate back to the closest upstream gateway for either handling by a custom bean or re-throwing by the gateway. Note that a custom release strategy on the Aggregator is difficult to use and especially so alongside timeouts but would not help in this case as the exception will propagate back to the leftmost gateway before the aggregator is invoked. It's also possible to configure exception handlers on the innermost gateways, the exception message could be caught but how do you route messages from a custom exception handler into the aggregator to complete the group, inject the aggregator channel definition into the custom exception handler? This is a poor approach and would involve unpacking an exception message payload, copying the original message headers into a new SI message and then adding the original payload - only four or five lines of code, but dirty it is. Following exception generation, exception messages (without modification) cannot be routed into an Aggregator to complete the group. The original message, the one that contains the correlation and sequence ids for the group and group position are buried inside the SI messages exception payload. If processing needs to continue following exception generation, it should be clear that in order to continue processing, the following must take place: the aggregation group needs to be completed, any exceptions must be caught and handled before getting back to the closet upstream gateway, the correlation and sequence identifiers that allow group completion in the aggregator are buried within the exception message payload and will require extraction and setting on the message that's bound for the aggregator A More Robust Solution - Messaging Gateway Adapter Pattern Dealing with exceptions and null returns from gateways naturally leads to a design that implements a wrapper around the messaging gateway. This affords a level of control that would otherwise be very difficult to establish. This adapter technique allows all returns from messaging gateways to be caught and processed as the messaging gateway is injected into the Service Activator and called directly from that. The messaging gateway no longer responds to the aggregator directly, it responds to a custom Java code Spring bean configured in the Service Activator namespace definition. As expected, processing that does not undergo exception will continue as normal. Those flows that experience exception conditions or unexpected or missing responses from messaging gateways need to process messages in such as way that message groups bound for aggregation can be completed. If the Service Activator were to allow the exception to be propagated outside of it's backing bean, the group would not complete. The same applies not just for exceptions but any return object that does not carry the prerequisite group correlation id and sequence headers - this is where the adaptation is applied. Exception messages or null responses from messaging gateways are caught and handled as shown in the following example code: import com.l8mdv.sample.*; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.integration.Message; import org.springframework.integration.MessageHeaders; import org.springframework.integration.support.MessageBuilder; import org.springframework.util.Assert; public class AvsServiceImpl implements AvsService { private static final Logger logger = LoggerFactory.getLogger(AvsServiceImpl.class); public static final String MISSING_MANDATORY_ARG = "Mandatory argument is missing."; private AvsGateway avsGateway; public AvsServiceImpl(final AvsGateway avsGateway) { this.avsGateway = avsGateway; } public Message service(Message message) { Assert.notNull(message, MISSING_MANDATORY_ARG); Assert.notNull(message.getPayload(), MISSING_MANDATORY_ARG); MessageHeaders requestMessageHeaders = message.getHeaders(); Message responseMessage = null; try { logger.debug("Entering AVS Gateway"); responseMessage = avsGateway.send(message); if (responseMessage == null) responseMessage = buildNewResponse(requestMessageHeaders, AvsResponseType.NULL_RESULT); logger.debug("Exited AVS Gateway"); return responseMessage; } catch (Exception e) { return buildNewResponse(responseMessage, requestMessageHeaders, AvsResponseType.EXCEPTION_RESULT, e); } } private Message buildNewResponse(MessageHeaders requestMessageHeaders, AvsResponseType avsResponseType) { Assert.notNull(requestMessageHeaders, MISSING_MANDATORY_ARG); Assert.notNull(avsResponseType, MISSING_MANDATORY_ARG); AvsResponse avsResponse = new AvsResponse(); avsResponse.setError(avsResponseType); return MessageBuilder.withPayload(avsResponse) .copyHeadersIfAbsent(requestMessageHeaders).build(); } private Message buildNewResponse(Message responseMessage, MessageHeaders requestMessageHeaders, AvsResponseType avsResponseType, Exception e) { Assert.notNull(responseMessage, MISSING_MANDATORY_ARG); Assert.notNull(responseMessage.getPayload(), MISSING_MANDATORY_ARG); Assert.notNull(requestMessageHeaders, MISSING_MANDATORY_ARG); Assert.notNull(avsResponseType, MISSING_MANDATORY_ARG); Assert.notNull(e, MISSING_MANDATORY_ARG); AvsResponse avsResponse = new AvsResponse(); avsResponse.setError(avsResponseType, responseMessage.getPayload(), e); return MessageBuilder.withPayload(avsResponse) .copyHeadersIfAbsent(requestMessageHeaders).build(); } } Notice the last line of the catch clause of the exception handling block. This line of code copies the correlation and sequence headers into the response message, this is mandatory if the aggregation group is going to be allowed to complete and will always be necessary following an exception as shown here. Consequences of using this technique There's no doubt that introducing a Messaging Gateway Adapter into SI config makes the configuration more complex to read and follow. The key factor here is that there is no longer a linear progression through the configuration file. This because the Service Activator must forward reference a Gateway or a Gateway defined before it's adapting Service Activator - in both cases the result is the same. Resources Note:- The design for the software that drove creation of this meta-pattern was based on a requirement that a number of external risk assessment services would be accessed by a single, central Risk Assessment Service. In order to satisfy clients of the service, invocation had to take place in parallel and continue despite failure in any one of those external services. This requirement lead to the design of the Messaging Gateway Adapter Pattern for the project. Spring Integration Reference Manual The solution approach for this problem was discussed directly with Mark Fisher (SpringSource) in the context of building Risk Assessment flows for a large US financial institution. Although the configuration and code is protected by NDA and copyright, it's acceptable to express the design intention and similar code in this article.

I'm not even interested in psychology. But. This kind of thing seems to come up once in a great while. You're asked (or "forced") to work with someone who—essentially—fails to cooperate. They don't actively disagree or actively suggest something better. They passively fail to agree. In fact, they probably disagree. They may actually have an idea of their own. But they prefer to passively "fail to agree." I have little patience to begin with. And I had noted my personal inability to cope in The Passive-Aggressive Programmer or Why Nothing Gets Done. Recently, I received this. "I thought I was going crazy and started doubting myself when dealing with a PAP co-worker. I went out on the internet searching for help and ran into your blog and its helped me realize that I'm not crazy. The example conversations you posted are almost every day occurrences here at my job when dealing with my co-worker. From outside of the department it was oh those two just butt-heads because I never knew how to communicate or point out that really I'm a targeted victim of a PAP rather than a butting heads issue. No matter what approach I took with the PAP I was doomed and still not quite sure where to go from here. Would you happen to offer any advice on how to actually deal with PAP? It's driven me to a point where I'm looking for new employment because my employer won't deal with it." I really have no useful advice. There's no way to "force" them to agree with anything specific. In some cases, there's no easy to even determine what they might agree with. Your employer will only "deal with" problems that cause them real pain. If you're butting heads, but still getting things done, then there's no real pain. You're successful, even if you're unhappy. If you want to be both happy and successful, you need to stop doing things that make you unhappy. If you can't agree with a co-worker, you can butt heads (which makes you unhappy) or you can ignore them (which may make you happy.) Ignoring them completely may mean that things will stop getting done. You may appear less successful. If you stop being successful, then your employer will start to feel some pain. When you employer feels pain, they will take action to relieve the pain. You might want to try to provide clear, complete documentation of your colleague's ideas, whatever they are. If you write down the Passive-Aggressive Programmer's "suggestions", then you might be able to demonstrate what's causing the pain. Since a properly passive programmer never actually agrees with anything, it's tricky to pin them down to anything specific. You might be able to make it clear that they're the roadblock that needs to be removed.

Blogging was quite a trend a few years ago, but with the rise of Facebook & Twitter, it’s fallen out of favor with some. Well, I’m here to tell you that you should open your own blog today, and if you own a blog but haven’t posted in a while … you should come back to it and post some more. There are several reasons for maintaining a blog, some of which I’m sure are relevant to you: Reason 1 – A technical memento to your future self I found out today how to do something cool. In a year, I won’t remember how to do it … but I might remember it enough to know what to look for. Once I’ve blogged about something, if I Google for it in the future I often find my own blog post, and save myself a considerable amount of time. There are other venues for such mementos-to-self, but none as indexable and expressive as a blog post. Facebook content is poorly searchable … I searched for something I posted 2 days ago on Facebook and failed to find it except going over my stream/timeline. Twitter is very limiting … I guess it might be good for something, but not for keeping concrete knowledge about how to solve a problem, except that knowledge is just a link. You could post a Stack Overflow or Quora question, and answer it, but that feels kind of akward. Actually, Quora has Boards which are rather similar to blogs for this purpose. Reason 2 – Why not share the love? An immediate followup to Reason#1 – if you worked hard and found out something, why not share it and save some time for other people who might run into the same problem? It’s just being a good citizen, and it doesn’t cost you more effort to share it rather than keep it in a private knowledge base e.g. Evernote / Google Docs. If you’ve ever Googled and found a blog post that solved your problem – now is your time to give something back. Reason 3 – Professional Resume Your blog tells the world about you. Whenever I interview for a job, the first thing on my resume is my blog. It shows that I am passionate about my profession. Even if your blog is just a collection of links, it shows what kind of technology stack you’re using or interested in, what your beliefs are, and what makes you tick. I’ll give a candidate with a personal blog a big +1 over a candidate without a blog any time. It takes courage to go out there and say “Even though I’m not worthy, I’m still out here, doing, writing, and sharing. I’m not the best software engineer / biologist / whatever in the world … but I’m trying my best, and I want to share it with you”. Reason 4 - Alzheimer This is an extension of reason 1. Reason 1 was about forgetting technical stuff … but as the years pass, you don’t just forget technical stuff, you forget who you were. Your life isn’t lived by a single personality, but is rather experienced by an endless series (or continuum) of personalities, each slightly different than the ones before it. I hardly remember what things we like twenty years ago … but I do know that 5 years ago, I felt the immense joy of leaving the army, didn’t like Google for a day, and had loads of fun playing Portal. I recently started maintaining, in addition to this blog and social media accounts, a personal record of how each day worked out for me. My setup is simple – I setup a Google Calendar event to send me a daily reminder at 7 PM each day. I forward this reminder to Evernote, and prefix it with a number between 1 and 5 of “how much I enjoyed this day”, plus a one liner of key events that happened. I have a grand plan to one day go over these notes, chart out my happiness graph, and note any specific events … but for the time being I’m recording. A blog can serve to record part of your history – the part you’re willing to be public about, of course. I picture my kids, ten or twenty years from now, reading through my blog (yeah right, all hundreds of entries , to learn who their father was back on 2012, when we didn’t have hovercrafts and teleportation. Maybe it will happen, maybe it won’t, but I know that I would have been happy if my parents had kept such a diary. Reason 5 – Helping semi-distant friends keep in touch I have 267 friends on Facebook … guess with how many I actually keep in touch in real life? I guess maybe ten-fifteen max, and the real number is probably more close to five. But, thanks to Facebook, I get to not lose my other friends completely. Even though I don’t spend enough time with them, I get occasional glimpses of their lives. The problem with social networks is you can’t possibly keep up with everything … I even miss cool posts like this one because they’re swallowed up in a huge stream of noise. A part of the fix is blogging. When you have a blog, I’ll follow it with my trusty Google Reader, and it won’t get swallowed up, because I do read or glance everything in my reader stream. So please, if you’re a friend of mine, do me a personal favor and blog – I want to keep in touch with you! Summary Please, don’t give me bullshit like “You don’t have anything worth writing about” or “You’re not a good enough writer”. Perfect is the enemy of good … just start by writing something, it’s better by any definition than not writing anything. If you care about it, work on your writing and save up interesting bits to write later (I was saving the idea for this post for a couple of months now, until I got the time and energy to write it). Stuff happens in your life, both personal & professional. Save up the good parts, and write … your future self + children will thank you later.

eclipse comes with a large set of different views: they allow the developer to represent the information in various forms and with different angles. most of these views are navigation oriented: a perfect example for this is the projects view or the outline view . but over time i add more projects, more resources to my project, and at a certain time things get overwhelming. i have a lot of projects, and i do not want to switch between workspace too often. yes, i can open and close projects, but this gets cumbersome too. thankfully, there is a solution in eclipse: working sets . working sets allow me to group elements for display in views. with that, i can do operations on a set of elements in that working set. especially as i’m using many projects the same time, working sets are a big help to focus on the right set of things at a time. i can define a set of things i want to look at, work with, or whatever: it allows me to get be productive in the universe of my environment. building/compiling a working set a nice feature of using working sets is to build a set of projects. instead of selecting a set of projects and then to compile them together, i use a working set. i use the menu project > build working set > select working set… to create or change working sets: menu to select working set if i have no working set defined, then this will show the following dialog where i can press new… to create a new one: creating new working set to create a working set of c/c++ projects, i select c/c++ and press next : new c c++ working set next i give a name and select the project(s) which shall be in my working set, and press finish : defining working set to build my set of projects, i can select the working set and press ok : selected working set search in a working set it is possible to limit the search to a working set. for this i can choose a working set as scope in the search dialogs: search in a working set managing working sets to manage working sets, i press ctrl+3 (see quick access ) and choose manage working sets… : ctrl+3 with manage working sets… note: i can add extra tool-bars and menus for working sets too (this is explained later). then i can manage my working sets: manage working set configuration project view filtering with working sets i can filter the projects shown in the project view based on working sets. for this i select the small triangle and select/define a working set or choose one from the most recently used sets: working sets for project view with this i can easily filter and focus on a subset of projects: project view with applied working set really cool tip: i’m using working sets as well to avoid too many workspaces. instead of having projects spread over different workspaces, i can keep them in one workspace and use working sets instead. there is an added benefit of using working sets: having too many projects open at the same time in eclipse can slow down the ide: using working sets allows me just to switch quickly between the set of projects i’m working on. but it does not stop at filtering by projects: you can filter even things inside the project structure. i simply deselect things i don’t want to see and can focus on what is important for me: filtering project files export and import of working sets note: import and export of working sets is not part of the standard codewarrior eclipse distribution. you get the import/export feature installed with the mqx plugins (www.freescale.com/mqx) or with the anyedit plugins (http://andrei.gmxhome.de/anyedit/index.html). to export a working set, i use the menu file > export > other > export working set : export working sets with mqx plugins note: the anyedit plugins come as well with an import/expert working set wizard. the file format is different, and the mqx plugin allows drag&drop of the file into eclipse. this gives the following dialog where i can specify the file name and the root of projects: export working set dialog this will store the settings in an xml file. importing the working set is done with file > import > other > import working set . tip: i’m using *.wsd extension for working sets. that way i can simply drag&drop the file into eclipse to import it. other kinds of working sets working sets do not stop at projects and files: select working set type i can create working sets of breakpoints or analysis/trace points. or i can create working sets of any resource files or tasks. the possibilities are nearly endless and depend as well on the extra plugins installed. window working sets and now back to the really cool part. one question remains: what are window working sets? window working sets the thing is that every view and dialog has its own working set setting. in my example below i use a working set ‘coldfire’ for the projects view, but my search dialog has a ‘kinetis’ working set configured: two different working sets sometimes i want this, but not always. what i need is a ‘global’ working set. and here the window working sets comes to rescue me. for this i’m going to add some menus and toolbars to make it really easy… for this i choose the menu window > customize perspecti ve. in the command groups i enable ‘window working set’. additionally it is a good idea to enable ‘working set manipulation’ as well: window working set commands the same way i can enable the toolbar and menu visibility. this gives me added tool-bars to switch between working sets and to add/remove things from a working set quickly: working set toolbars in a similar way, it gives me menu access as well: working sets menu and here is the trick: using ‘ window working set ‘ really means ‘ using the global workbench working set ‘. to select the global workbench working set, i use the toolbar icon to switch between window (or workbench) working sets: selecting global window or workbench working set in the individual views i choose to use the window working sets instead a selection of working sets: selected global window or workbench working set now my working set settings are shared and common for all views: if i switch the working set, it will switch for all views where i have set it to ‘window working set’: window working set applied to multiple views that way my working set is the same across views, and switching between different project settings is done with a simple mouse click. summary working sets are an extremely powerful feature to get focus on a subset of things inside eclipse, based on my workflow. as with many great eclipse features, i need to know about it until you really appreciate the power of it. who knows how many other hidden treasures are buried in eclipse i hope this article helps to save you a few mouse clicks. happy work-setting but over time i add more projects, more resources to my project, and at a certain time things get overwhelming. i have a lot of projects, and i do not want to switch between workspace too often.

Today I will debunk quite a popular myth about one way only communication in JMS. There is no classic request-response equivalent of course (just like there is in AMQP), but a message may convey a reply to header containing a reference to a temporary queue. This way we can achieve two way communication in JMS. Below I give you a simple JUnit test which illustrates the idea. Example In the following example I use a temporary queue and set it as JMS reply to header. The temporary queue exists as long as its creator's session is active. The code is pretty simple and self commenting. In testA I create a message and a temporary queue which I expect to recieve a response from the consumer. Comsumer in testB consumes the message, retrieves the reply to destination and sends a text message to it. testC consumes the message from temporary queue. Once the session is closed, temporary queue is disposed and removed. public class AppTest { private static Connection connection; private static Session session; private static Destination destination; private static Destination replyToDestination; @BeforeClass public static void setup() throws JMSException { ConnectionFactory connectionFactory = new ActiveMQConnectionFactory( "tcp://localhost:62626"); connection = connectionFactory.createConnection(); connection.start(); session = connection.createSession(true, Session.SESSION_TRANSACTED); destination = session.createQueue("Java.ActiveMQ.Test.Queue"); replyToDestination = session.createTemporaryQueue(); } @AfterClass public static void cleanup() throws JMSException { session.close(); connection.stop(); connection.close(); } @Test public void testA() throws JMSException { MessageProducer producer = session.createProducer(destination); Person person = new Person(); person.setFirstName("Lukasz"); person.setLastName("Budnik"); Message message = session.createObjectMessage(person); message.setJMSReplyTo(replyToDestination); producer.send(message); session.commit(); } @Test public void testB() throws JMSException, InterruptedException { Person person = null; MessageConsumer consumer = session.createConsumer(destination); Message message; while ((message = consumer.receive(2000l)) != null) { if (message instanceof ObjectMessage) { ObjectMessage objectMessage = (ObjectMessage) message; Object object = objectMessage.getObject(); if (object instanceof Person) { person = (Person) object; Assert.assertEquals("Lukasz", person.getFirstName()); Assert.assertEquals("Budnik", person.getLastName()); Destination replyToDestination = message.getJMSReplyTo(); MessageProducer replyToMessageProducer = session.createProducer(replyToDestination); Message replyMessage = session.createTextMessage("OK"); replyToMessageProducer.send(replyMessage); session.commit(); } } } if (person == null) { Assert.fail("Person is null"); } } @Test public void testC() throws JMSException, InterruptedException { String text = null; MessageConsumer consumer = session.createConsumer(replyToDestination); Message message; while ((message = consumer.receive(2000l)) != null) { if (message instanceof TextMessage) { TextMessage textMessage = (TextMessage) message; text = textMessage.getText(); Assert.assertEquals("OK", text); session.commit(); } } if (text == null) { Assert.fail("Text is null"); } } } Summary Simple, isn't it? This mechanism is used heavily in Apache Camel and WS frameworks which use transacted JMS under the hood for WS-RM implementations. Using those frameworks, temporary queues and reply to headers are being taken care of transparently so I may even not know that you use them :) cheers, Łukasz

Spring Integration (SI) Gateways Spring Integration Gateways () provide a semantically rich interface to message sub-systems. Gateways are specified using namespace constructs, these reference a specific Java interface () that is backed by an object dynamically implemented at run-time by the Spring Integration framework. Furthermore, these Java interfaces can, if you so wish, be defined entirely independent of any Spring artefacts - that's both code and configuration. One of the primary advantages of using the SI gateway as an interface to message sub-systems is that it's possible to automatically adopt the benefit of rich, default and customisable, gateway configuration. One such configuration attribute deserves further scrutiny and discussion primarily because it's easy to misunderstand and misconfigure around - default-reply-timeout. Primary Motivator for Gateway Analysis During recent consulting engagements, I've encountered a number of deployments that use Spring Integration Gateway specifications that may, in some circumstances, lead to production operational instability. This has often been in high-pressure environments or those where technology support is not backed by adequate training, testing, review or technology mentoring. How do gateways behave in Spring Integration (R2.0.5) One of the key sections, regarding gateways, in the Spring Integration manual clearly explains gateway semantics. Below is a 2-dimensional table of possible non-standard gateway returns for each of the scenarios that the SI Manual (r2.0.5) refers to. Gateway Non-standard Responses Runtime Events default-reply-timeout=x Single-threaded default-reply-timeout=x Multi-threaded default-reply-timeout=null Single-threaded default-reply-timeout=null Multi-threaded 1. Long Running Process Thread Parked null returned Thread Parked Thread Parked 2. Null Returned Downstream null returned null returned Thread Parked Thread Parked 3. void method Downstream null returned null returned Thread Parked Thread Parked 4. Runtime Exception Error handler invoked or exception thrown. Error handler invoked or exception thrown. Error handler invoked or exception thrown. Error handler invoked or exception thrown. The key parts of this table are the conditions that lead to invoking threads being parked (noted in red), nulls returned (noted in orange) and exceptions (noted in green). Each contributor consists of configuration that is under the developers control, deployed code that is under developers control and conditions that are usually not under developers control. Clearly, the column headings in the table above are divided into two sections; two gateway configuration attributes. The default-reply-timeout is set by the SI configured and is the amount of time that a client call is wiling to wait for a response from the gateway. Secondly, synchronous flows are represented by Single-threaded flows, asynchronous by Multi-threaded flows. A synchronous, or single-threaded flow, is one such as the following: The implicit input channel (gateway-request-channel) has no associated dispatcher configured. An asynchronous, or multi-threaded flow, is one such as the following: The explicit input channel has a dispatcher configured ("taskExecutor"). This task executor specifies a thread pool that supplies threads for execution and whose configuration as above marks a thread boundary. Note: This is not the only way of making channels asynchronous The other configuration attribute referenced is default-reply-timeout, this is set on the gateway namespace configuration such as the example above. Note that both of these runtime aspects are set by the configurer during SI flow design and implementation. They are entirely under developer control. The 'Runtime Events' column indicates gateway relevant runtime events that have to be considered during gateway configuration - these are obviously not under developer control. Trigger conditions for these events are not as unusual as one may hope. 1. Long Running Processes It's not uncommon for thread pools to become exhausted because all pooled threads are waiting for an external resource accessed through a socket, this may be a long running database query, a firewall keeping a connection open despite the server terminating etc. There is significant potential for these types of trigger. Some long-running processes terminate naturally, sometimes they never completed - an application restart is required. 2. Null returned downstream A null may be returned from a downstream SI construct such as a Transformer, Service Activator or Gateway. A Gateway may return null in some circumstances such as following a gateway timeout event. 3. Void method downstream Any custom code invoked during an SI flow may use a void method signature. This can also be caused by configuration in circumstances where flows are determined dynamically at runtime. 4. Runtime Exception RuntimeException's can be triggered during normal operation and are generally handled by catching them at the gateway or allowing them to propagate through. The reason that they are coloured green in the table above is that they are generally much easier to handle than timeouts. Gateway Timeout Handling Strategies There are four possible outcomes from invoking a gateway with a request message, all of these as a result of specific runtime events: a) an ordinary message response, b) an exception message, c) a null or d) no-response. Ordinary business responses and exceptions are straight forward to understand and will not be covered further in this article. The two significant outcomes that will be explored further are strategies for dealing with nulls and no-response. Generally speaking, long running processes either terminate or not. Long running processes that terminate may eventually return a message through the invoked gateway or timeout depending on timeout configuration, in which case a null may be returned. The severity of this as a problem depends on throughput volume, length of long running process and system resources (thread-pool size). Configuration exists for default-reply-timeout In the case where a long running process event is underway and a default-reply-timeout has been set, as long as the long running process completes before the default-reply-timeout expires, there is no problem to deal with. However, if the long running process does not complete before that timeout expires one of three outcomes will apply. Firstly, if the long running process terminates subsequent to the reply timeout expiry, the gateway will have already returned null to the invoker so the null response needs handling by the invoker. The thread handling the long-running process will be returned to the pool. Secondly, if the long running process does not terminate and a reply timeout has been set, the gateway will return null to the gateway invoker but the thread executing the long-running process will not get returned to the pool. Thirdly, and most significantly, if a default-reply-timeout has been configured but the long running process is running on the same thread as the invoker, i.e. synchronous channels supply messages to that process, the thread will not return, the default-reply-timeout has no affect. Assuming the most common processing scenario, a long running process completes either before or after the reply timeout expiry. When a null is returned by the gateway, the invoker is forced to deal with a null response. It's often unacceptable to force gateway consumers to deal with null responses and is not necessary as with a little additional configuration, this can be avoided. Absent Configuration for default-reply-timeout The most significant danger exists around gateways that have no default-reply-timeout configuration set. A long running process or a null returned from downstream will mean that the invoking thread is parked. This is true for both synchronous and asynchronous flows and may ultimately force an application to be restarted because the invoker thread pool is likely to start on a depletion course if this continues to occur. Spring Integration Timeout Handling Design Strategies For those Spring Integration configuration designers that are comfortable with gateway invokers dealing with null responses, exceptions and set default-reply-timeouts on gateways, there's no need to read further. However, if you wish to provide clients of your gateway a more predictable response, a couple of strategies exist for handling null responses from gateways in order that invokers are protected from having to deal with them. Firstly, the simpliest solution is to wrap the gateway with a service activator. The gateway must have the default-reply-timeout attribute value set in order to avoid unnecessary parking of threads. In order to avoid the consequence of long-running threads it's also very prudent to use a dispatcher soon after entry to the gateway - this breaks the thread boundary. Whilst this is a valid technical approach, the impact is that we have forced a different entry point to our message sub-system. Entry is now via a Service Activator rather than a Gateway. A side affect of this change is that the testing entry point changes. Integration tests that would normally reference a gateway to send a message now have to locate the backing implementation for the Service Activator, not ideal. An alternative approach toward solving this problem would be to configure two gateways with a Service Activator between them. Only one of the gateways would be exposed to invokers, the outer one. Both Gateways would reference the same service interface. The outer gateway specification would not specify the default-reply-timeout but would specify the input and output channels in the same way that a single gateway would. The Service Activator between the Gateways would handle null gateway responses and possibly any exceptions if preferred to the gateway error handler approach. An example is as follows: The Service Activator bean (enrollmentServiceGatewayHandler) deals with both null and exception responses from the adapted gateway (enrollmentServiceAdaptedGateway), in the situation where these are generated a business response detailing the error is generated. Spring Integration R2.1 Changes async-executor on gateway spec

After my article Connection Pooling in a Java Web Application with Glassfish and NetBeans IDE, here are the instructions for Tomcat. Requirements NetBeans IDE (this tutorial uses NetBeans 7) Tomcat (this tutorial uses Tomcat 7 that is bundled within NetBeans) MySQL database MySQL Java Driver Steps Assuming your MySQL database is ready, connect to it and create a database. Lets call it connpool: mysql> create database connpool; Now we create and populate the table from which we will fetch the data: mysql> use connpool; mysql> create table data(id int(5) not null unique auto_increment, name varchar(255) not null); mysql> insert into data(name) values("Fred Flintstone"), ("Pink Panther"), ("Wayne Cramp"), ("Johnny Bravo"), ("Spongebob Squarepants"); That is it for the database part. We now create our web application. In NetBeans IDE, click File → New Project... Select Java Web → Web Application: Click Next and give the project the name TomPool. Click Next Choose the server as Tomcat and, since we are not going to use any frameworks, click Finish. The project will be created and the start page, index.jsp, opened for us in the IDE. Now we create the connection pooling parameters. In the Projects window, expand configuration files and open "context.xml". You will see that the IDE has added this code for us: Delete the last line: and then add the following to the context.xml file. I have explained the sections along the way. Make sure you edit your MySQL username and password appropriately: Next, expand the Web Pages node, right-click WEB-INF → New → Other → XML → XML Document. Click Next and type web for the File Name. Click next and choose Well-Formed Document then Finish. You will now have the file "web.xml": Delete everything in the file and paste this code: MySQL Test App DB Connection connpool javax.sql.DataSource Container That is it for the connection pool. We now edit our code to make use of it. Edit index.jsp by adding this code just after the initial coments but before Edit the section of the page: Data in my Connection Pooled Database Now, we test the connection pool by running the application: If you want to have the one connection pool used in multiple applications, you need to edit the following two files: 1. /conf/web.xml Just before the closing tag, add the code DB Connection connpool javax.sql.DataSource Container 2. /conf/context.xml Just before the closing tag, add the code Now you can use the pool without editing XML files in each of your applications. Just use the sample code as given in index.jsp That's it folks!

CamelOne was yet again a really cool and fun conference. I just returned back home, from the 2nd annual CamelOne conference, held in downtown Boston. It was a 2 day packed with great talks with a balanced mix of technical talks, cloud stuff, and showcases of integration in the real world. CamelOne speaker podium The feedback of the conference was really good, as you can see from the image below. Feedback wall from CamelOne attendees The FuseSource engineering team was present, and on the end of the 2nd day, Debbie, got us together for a photo session. The FuseSource Engineering Team CamelOne 2012 - Day 1 So back the the 1st day. This year Jonathan and I was asked to do the opening key note, with our Camel story, and where the Camel project is today, and some thoughts about how Camel could be riding the cloud in the near future. Jonathan and I wanted to tell our Camel story with a sense of humor. I can say mission accomplished when the slide with the lovely Camel picture was shown. And no the picture is not retouched, it was found using google image search. Apache Camel is a project that stands out After the keynote I gave a talk about how to get started riding the Camel. The talk is a practical focus talk so I was sharing the time 50/50 between slides and live coding. As all sessions were recorded, and we can all watch them later, as they will be posted on the CamelOne website, free for anymore to watch. A professional production company is currently processing the videos. They should be ready in weeks from now. I will blog when the videos are online. Free Apache/Fuse Resources Apache Project Leader Videos Open Source Integration Tool Downloads Integrate Anywhere: Fuse ESB Super Fast Messaging with Fuse MQ Free SOA Webcasts Apache ActiveMQ and ServiceMix Lessons Integration Resources Jonathan was next after my talk, and his talk was a natural progress from mine talk. As he gave a rundown how you can run and deploy Camel and CXF applications in the ESB server. Jonathan showed how this works in practice as well. I got engaged in a number of hallway conversations, and didn't have the chance to attend a session at every slot. It was really great to meet so many happy Camel users, and hear their stories, where the Camel is riding in the real world. Also I was told that more and more commercial vendors is adapting Camel and embedding it internally in their commercial products. Kai Wahner gave his first of two talks today. Kai Wahner giving a talk about choosing Integration Frameworks He was talking about his experience with evaluating Apache Camel, Spring Integration, and Mule ESB. I guess Camel was in favor at a Camel conference :) James gave the ending general session of the first day. James Strachan giving ending key note on 1st day As always a pleasure to watch James talk with such a enthusiasm. His talk was a technical talk addressed to the developers how to develop and get Camel riding in the cloud. He gave a tour of the cool and awesome much improved Fuse IDE 2.1 product. It now has even more Camel crack for runtime insight. As well as easier deployment for both local jvms, remove machines, and as well the clouds. CamelOne 2012 - Day 2 On the 2nd day, we have Gabe Zichermann giving a very entertaining keynote, about gamification. Gabe talking about Gamification The idea of getting people engaged, based on the ideas of computer games. But applying them in a real life processes. For example a company managed to get its employees go to the gym, based on teaming up, and competing against your co-workers. In Sweden they have traffic cameras, using reverse sychology, by enlisting people in a lottery, if they are within speed limits. However people above the speed limit will of course still get a fine, and not participate in the lottery. I have heard good buzz about Stan Lewis and Dhirajs talk about how to manage, monitor and provision a cluster of machines, in a data centre or the cloud. Dhiraj showed how Fuse HQ could monitor the Camel applications running on numerous machines. And how that worked as well when Stan did a rolling upgrade on the fly, leaving Fuse HQ being able to compare and display a "before" vs. "after" overview. Likewise the tweets about Charles Moulliard were very positive. Seems like people wanted to go and play with websockets, and the Camel. This is definitly cool. So Camel 2.10 is a much anticipated release, having the websocket component out of the box. Kai was on the stage again, giving a talk about using Apache Camel with BPM (Avtiviti). Kai gave us a rundown of the differences between Camel and Activiti, and where they overlap. As well when you should use either one, or both of them. In Kais talk he give live demos which is a nice change in the flow, to see the "code" for real. Activiti and Camel together seems powerful. And the Activiti designer looks beautiful. Did you know that Camel is help protecting the Canadians. Mike Gingell from General Dynamics Canada gave us a rundown of how they have been successful by using open source integration technologies from Apache. The Camel is helping in cool stuff such as with the marine to detect torpedo attacks, with satellite surveillance of the north poles, and to keep track of personel and whatnot. Torpedo Warning System. Slide from Mike Gingell, General Dynamics Canada, Mike gave a really great talk, and also took us through how his team is battling uphill in a traditionally conservative organization where software projects take millions of $ and years to just get started. They have been on the open source road for about 5 years, and jumped on Apache ServiceMix when it became OSGi based. And the Camel has been riding all along together with ActiveMQ and CXF. So the Camel is help protecting Jonathan Anstey, who lives in New Foundland, Canada. Must be cool to know that the software he works on every day, is now serving the people of Canada. The ending keynote, was a real treat to all of us. Felix Ehmn from CERN gave us a very interesting talk how CERN is using ActiveMQ in their control room, to monitor the most complex machine man have ever built - the Large Hadron Collider; eg the 27km circle where they smash atoms together and see what happens. Felix giving ending keynote, about CERN using ActiveMQ There is 85.000 devices, which they need the monitor. Its everything, from censors on the collider, to fire alarms, door buttons and whatnot. CERN is definitily a cool place. In fact the coolest place on earth as well, as they need to cool down the collider, to 1 degree kelvin. That is - 272 degrees celsius. Like CERN, the CamelOne conference was very cool. I discovered a number of other blogs covering the CamelOne 2012 conference Kai Waehner blogged his CamelOne report. Christian Posta blogged as well And Rob Terpilowski who gave a talk also Hope to see you in 2013 at the next CamelOne conference. As David Reiser tweeted, the conference was awesome. David liked the conference

Some time ago I came across What's the purpose of AsyncContext.start(...) in Servlet 3.0? question. Quoting the Javadoc of aforementioned method: Causes the container to dispatch a thread, possibly from a managed thread pool, to run the specified Runnable. To remind all of you, AsyncContext is a standard way defined in Servlet 3.0 specification to handle HTTP requests asynchronously. Basically HTTP request is no longer tied to an HTTP thread, allowing us to handle it later, possibly using fewer threads. It turned out that the specification provides an API to handle asynchronous threads in a different thread pool out of the box. First we will see how this feature is completely broken and useless in Tomcat and Jetty - and then we will discuss why the usefulness of it is questionable in general. Our test servlet will simply sleep for given amount of time. This is a scalability killer in normal circumstances because even though sleeping servlet is not consuming CPU, but sleeping HTTP thread tied to that particular request consumes memory - and no other incoming request can use that thread. In our test setup I limited the number of HTTP worker threads to 10 which means only 10 concurrent requests are completely blocking the application (it is unresponsive from the outside) even though the application itself is almost completely idle. So clearly sleeping is an enemy of scalability. @WebServlet(urlPatterns = Array("/*")) class SlowServlet extends HttpServlet with Logging { protected override def doGet(req: HttpServletRequest, resp: HttpServletResponse) { logger.info("Request received") val sleepParam = Option(req.getParameter("sleep")) map {_.toLong} TimeUnit.MILLISECONDS.sleep(sleepParam getOrElse 10) logger.info("Request done") } } Benchmarking this code reveals that the average response times are close to sleep parameter as long as the number of concurrent connections is below the number of HTTP threads. Unsurprisingly the response times begin to grow the moment we exceed the HTTP threads count. Eleventh connection has to wait for any other request to finish and release worker thread. When the concurrency level exceeds 100, Tomcat begins to drop connections - too many clients are already queued. So what about the the fancy AsyncContext.start() method (do not confuse with ServletRequest.startAsync())? According to the JavaDoc I can submit any Runnable and the container will use some managed thread pool to handle it. This will help partially as I no longer block HTTP worker threads (but still another thread somewhere in the servlet container is used). Quickly switching to asynchronous servlet: @WebServlet(urlPatterns = Array("/*"), asyncSupported = true) class SlowServlet extends HttpServlet with Logging { protected override def doGet(req: HttpServletRequest, resp: HttpServletResponse) { logger.info("Request received") val asyncContext = req.startAsync() asyncContext.setTimeout(TimeUnit.MINUTES.toMillis(10)) asyncContext.start(new Runnable() { def run() { logger.info("Handling request") val sleepParam = Option(req.getParameter("sleep")) map {_.toLong} TimeUnit.MILLISECONDS.sleep(sleepParam getOrElse 10) logger.info("Request done") asyncContext.complete() } }) } } We are first enabling the asynchronous processing and then simply moving sleep() into a Runnable and hopefully a different thread pool, releasing the HTTP thread pool. Quick stress test reveals slightly unexpected results (here: response times vs. number of concurrent connections): Guess what, the response times are exactly the same as with no asynchronous support at all (!) After closer examination I discovered that when AsyncContext.start() is called Tomcat submits given task back to... HTTP worker thread pool, the same one that is used for all HTTP requests! This basically means that we have released one HTTP thread just to utilize another one milliseconds later (maybe even the same one). There is absolutely no benefit of calling AsyncContext.start() in Tomcat. I have no idea whether this is a bug or a feature. On one hand this is clearly not what the API designers intended. The servlet container was suppose to manage separate, independent thread pool so that HTTP worker thread pool is still usable. I mean, the whole point of asynchronous processing is to escape the HTTP pool. Tomcat pretends to delegate our work to another thread, while it still uses the original worker thread pool. So why I consider this to be a feature? Because Jetty is "broken" in exactly same way... No matter whether this works as designed or is only a poor API implementation, using AsyncContext.start() in Tomcat and Jetty is pointless and only unnecessarily complicates the code. It won't give you anything, the application works exactly the same under high load as if there was no asynchronous logic at all. But what about using this API feature on correct implementations like IBM WAS? It is better, but still the API as is doesn't give us much in terms of scalability. To explain again: the whole point of asynchronous processing is the ability to decouple HTTP request from an underlying thread, preferably by handling several connections using the same thread. AsyncContext.start() will run the provided Runnable in a separate thread pool. Your application is still responsive and can handle ordinary requests while long-running request that you decided to handle asynchronously are processed in a separate thread pool. It is better, unfortunately the thread pool and thread per connection idiom is still a bottle-neck. For the JVM it doesn't matter what type of threads are started - they still occupy memory. So we are no longer blocking HTTP worker threads, but our application is not more scalable in terms of concurrent long-running tasks we can support. In this simple and unrealistic example with sleeping servlet we can actually support thousand of concurrent (waiting) connections using Servlet 3.0 asynchronous support with only one extra thread - and without AsyncContext.start(). Do you know how? Hint: ScheduledExecutorService. Postscriptum: Scala goodness I almost forgot. Even though examples were written in Scala, I haven't used any cool language features yet. Here is one: implicit conversions. Make this available in your scope: implicit def blockToRunnable[T](block: => T) = new Runnable { def run() { block } } And suddenly you can use code block instead of instantiating Runnable manually and explicitly: asyncContext start { logger.info("Handling request") val sleepParam = Option(req.getParameter("sleep")) map { _.toLong} TimeUnit.MILLISECONDS.sleep(sleepParam getOrElse 10) logger.info("Request done") asyncContext.complete() } Sweet!

As you know in the last months I've been intrigued more and more by metaphors for object-oriented systems, since they brilliantly solve the problem of naming by borrowing terminology from an existing field. However, it is also interesting (and indeed has happened many times) to propose metaphors for a software development process. Analogies like building a skyscraper and growing a crop have let us ground some of our hypothesis in "thousand-years old domains"; and often lead us ashtray by false comparisons like the one between programmers and bricklayers. The goal of this article is to describe the surgery metaphor for software development and check where it is useful to explain development concepts to newcomers and non-technical people. Quality There are some shared values between surgery and a certain category of software development, that deeply cares about the quality of the final product. For example, the diatribe of long-term and short-term value is resolved in favor of a the former: a solution must work without requiring larger operations for years (ideally, for decades). The cost of maintenance is taken into account and never discounted when discussing different approaches to the current problem. Attention to the detail is omnipresent in surgery, down to the singles procedure to follow; software development faces risk by automating most of these checks: broken builds cannot be deployed, and business metrics like current active users or satisfied requests must be monitored to ensure availability of the service. TDD and refactoring Following Uncle Bob's metaphor, common Agile practices like TDD are akin to aseptic techniques in surgery. These procedures started out simply by hand washing, and has evolved into gloves, masks and sterilization. Thus practices are not strictly necessary conditions for success: emergency scenarios require to operate without it, like in the case of first aid. However, standardized procedures are facilitating conditions: not as strong as necessary, but able to improve the odds of a good outcome enough to show a good return on investment. Post-surgery infections were as common and lethal in medieval times as finding bugs in production is nowadays. However, practices are never a sufficient condition: you don't bring a postman into a surgery room, make him wash hands and tell him to operate (while many people tell him to code without even the hand washing part.). There is a whole set of training that he has to undergo before being able to make a positive contribution. Training The training of surgeons is one of the hardest in the world. Depending on the country, there are strong qualifications to obtain and associations of certified professionals that a surgeon must belong to in order to operate the profession. In cases of misconduct, a surgeon can be stopped or expelled from the order. Try imagining a programmer getting expelled for doing a sloppy job. However, given how certifications work in the field at this time, we still have much work to do before they become a reliable signal for employees. A big part of the medical training happens on the field (in hospitals and periodically in operating rooms), although the apprentice is usually never left in charge. Moreover, the training is never declared complete, and there is a costant update on the latest tools and techniques on the part of doctors. Their publication ofscientific papers and journals can be compared to our blogs and articles reporting the best (or good) practices of a field, although the selection system is based on peer review in the former case and on popularity in the latter. The issues A first way in which the metaphor fails is in the different definition of value: while maintaining software and adding new features to it is often necessary, the best surgical operation is still the one that is not performed. In this sense, the value of getting the application to work again would be preferred to the one of further product development. Another issue that we would face is the inflating cost and time needed for training of doctors, alghouth the long training may actually be necessary for such a delicate domain. After all, the surgeon's salary justifies the investment costs to become one. High compensation systems seem to be able to attract the best programmers as for the best surgeons in the market. The inflating costs of healthcare are instead more worrying. In the case of software, there is a trade-off between value (and so monetary revenue) produced and cost, while it is much more difficult to ethically quantify if the costs of medical procedures are worth bearing. What is happening in software is that there is absolutely no regulation on who can be a supplier in the market, and as such the average (and also median) quality of the products is terrifying. I'm not saying that you should adopt the values of medicine in your work, which can be a stretch for Wordpress applications, but that if you share them, the surgery metaphor becomes interesting for you. Software is as important as human lives only when they depend on it, in the case of biomedical and transportation systems such as pacemakers and flight control; other important categories of software are business critical, and as such economic metaphors will suit them more than the medical one.

Someone just asked me to define “best practices” for a collection of application deployments.