Since EF was released I have been a fan. However, every once in a while I’ll run into a table design situation that I am not sure how to handle with EF. This week, I needed to setup a self-referencing table in order to store some hierarchical data. A self referencing table is a table where the primary key on the table is also defined as a foreign key. Sounds a little confusing right? Let’s clarify the solution with an example. Let’s say I am building an application where I have a list of categories and subcategories. One of my top level categories is “Programming Languages” and under programming languages I have to subcategories which are “C#” and “Java”. In order to store this data I can use a single table with the following structure: The actual data would look like this: Just to clarify, a top level category will have a null value for the ParentId field. For all child categories the ParentId field is used as to represent its parent’s primary key value. As a programmer you may want to think about the ParentId field as a pointer. To complete the example lets take a look at the SQL used to create the table. CREATE TABLE [dbo].[Categories] ( [CategoryId] [int] IDENTITY(1,1) NOT NULL, [Name] [nvarchar](255) NOT NULL, [ParentId] [int] NULL, PRIMARY KEY CLUSTERED ( [CategoryId] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] GO ALTER TABLE [dbo].[Categories] WITH CHECK ADD CONSTRAINT [Category_Parent] FOREIGN KEY([ParentId]) REFERENCES [dbo].[Categories] ([CategoryId]) GO ALTER TABLE [dbo].[Categories] CHECK CONSTRAINT [Category_Parent] GO Upon examining the SQL, you should have noticed that the CategoryId is the primary key on the table and the ParentId field is a foreign key which points back to the CategoryId field. Since we have a key referencing a another key on the same table we can classify this this as a self-referencing table. Now that we fully understand what a self-referencing table is, we can move forward to the Entity Framework code. To get started we first need to create a simple C# object to represent the Category table. Of course, keep in mind that if you are using EF Code first you do not need to create the table or database ahead of time. I only showed the table first because I wanted to better illustrate what a self referencing table is. public class Category { public int CategoryId { get; set; } public string Name { get; set; } public int? ParentId { get; set; } } So far the Category class is very simple. However, we really want to add a few more properties in order to make this class useful. For example, if you are a child category you really want to be able to use dot notation to get the name of the parent category (e.g. subCategory.Parent.Name). Using EF, we will create a virtual property named Parent. By making the property virtual we are letting EF know that when this property is accessed we want to load some data. Based on your configuration settings and the code you use to retrieve your data (whether or not you used DbSet.Include), EF will lazy load or eager load this data. public class Category { public int CategoryId { get; set; } public string Name { get; set; } public int? ParentId { get; set; } public virtual Category Parent { get; set; } } Finally, we also want a property called Children so we can use dot notation to enumerate over the child categories. Once again, here is the modified class: public class Category { public int CategoryId { get; set; } public string Name { get; set; } public int? ParentId { get; set; } public virtual Category Parent { get; set; } public virtual ICollection Children { get; set; } } The final step is to let EF know how these properties are related to one another. This can be done using EF's fluent API. If you are new to EF and are unaware of the fluent API then you may want to read this article first. public class CommodityCategoryMap : EntityTypeConfiguration { public CommodityCategoryMap() { HasKey(x => x.CategoryId); Property(x => x.CategoryId) .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity); Property(x => x.Name) .IsRequired() .HasMaxLength(255); HasOptional(x => x.Parent) .WithMany(x => x.Children) .HasForeignKey(x => x.ParentId) .WillCascadeOnDelete(false); } } Hopefully you paid careful attention to the last section of code where we state the a Category has an optional Parent property. In database speak, this simply means that the ParentID field is nullable. The code also states that if a Category object can have zero or many children. In order to specify that a record is a child, we leverage the ParentId field to hold the primary key value of the parent record. As I mentioned earlier, if you are a programmer its easier to think of the ParentId field as a pointer. Finally, I disabled the cascade on delete option. This step is optional and probably based on your own personal preferences. If you enable cascade on delete and you delete a category that has 100 children then you will effectively remove 101 records. For whatever reason this scares me a little bit. Perhaps, my short career as a DBA caused me to not trust people with large volume delete statements. However, you may decide differently depending on your circumstances. Hopefully, this short EF tutorial will help you if you are working through a scenario where you need to capture and manipulate hierarchical data. If you have any questions please leave a comment.

Make sure your Apache Thrift services are secure with this awesome tutorial.

There is an increasing number of libraries which are described as high performance and have benchmarks to back that claim up. Here is a selection that I am aware of.

This is the fifth of a series of articles about Persistence with Spring. This article will focus on the configuration of transactions with Spring 3.1 and JPA. For a step by step introduction about setting up the Spring context using Java based configuration and the basic Maven pom for the project, see this article. The Persistence with Spring series: Part 1 – The Persistence Layer with Spring 3.1 and Hibernate Part 2 – Simplifying the Data Access Layer with Spring and Java Generics Part 3 – The Persistence Layer with Spring 3.1 and JPA Part 4 – The Persistence Layer with Spring Data JPA Part 5 – Transaction configuration with JPA and Spring 3.1 Spring and Transactions Spring provides a consistent and comprehensive transaction abstraction over many supported environments. There are two distinct ways of configuring and using transactions – annotations and AOP – each with their own advantages. The reference should provide enough material on both the decision to use the Spring transaction programming model, as well as a in depth discussion of its architecture. Configuring transactions with annotations After the introduction of Java based configuration in Spring 3.0, configuring transactions was one of the last things to require XML. Spring 3.1 introduces the new @Enable annotations - @EnableTransactionManagement – which makes it possible to fully use Java for the configuration: @Configuration @EnableTransactionManagement public class PersistenceJPAConfig{ @Bean public LocalContainerEntityManagerFactoryBean entityManagerFactoryBean(){ ... } @Bean public PlatformTransactionManager transactionManager(){ JpaTransactionManager transactionManager = new JpaTransactionManager(); transactionManager.setEntityManagerFactory( entityManagerFactoryBean().getObject() ); return transactionManager; } } However, if Java is not an option, here is the XML equivalent of this configuration: For a full discussion and code samples on configuring Spring with JPA, check out a previous article of this series. The @Transactional configuration By default, @Transactional will set the propagation to REQUIRED, the readOnly flag to false, and the rollback only for unchecked exceptions. Also note that the isolation level is set to the database default; when using JPA, the isolation level is that of the underlying persistence provider. In the case of Hibernate, the isolation level of all transactions should be REPEATABLE_READ. For the purpose of this discussion, the relevant application layers will be DAO, Service and Controller. These layers can of course vary from application to application, without changing the underlying principles discussed here. The @Transactional semantics of the Service and DAO layers should both be configured with REQUIRED propagation and the readOnly flag set to true for the relevant methods. The Controller layer should contain no transaction logic. Note that this is also the way the DAO implementation is configured in Spring Data. For a detailed analysis of the persistence layer with Spring data, see the previous article of this series. Assuming a clean separation of layers, where the Controller layer will only invoke the Service layer, which in turn will only call the DAO, then the DAO layer will never be called in a non-transactional context. As such the DAO will never be the transaction owner, and a more strict transaction configuration should be used for it. In this situation, the transactional semantics should be MANDATORY propagation and no readOnly flag. The MANDATORY propagation will simply ensure that a transaction has already been started when the DAO layer is entered, double checking the stated assumption that the DAO is never the transaction owner. The readOnly flag is also not needed because it will be set by the transaction owner as well. The API layer transaction strategy With the previous transaction configuration, the Service layer is the transaction owner – it is responsible with starting the transaction and it contains any potential rollback logic. This does however have one downside: a Service write method can invoke another Service write method; because both may contain rollback logic, the transaction owner may not have full control over the rollback logic in some circumstances. For this reason care must be taken if the transaction owner resubmits the transaction or takes corrective action – in these cases the service logic may need to be refactored to avoid this scenario. The API layer strategy is meant to address this shortcoming by making the Controller layer the transaction owner and working with the assumption that a public Controller method shouldn’t invoke another in any scenario. With this transaction strategy, the DAO and Service transactional semantics remain the same as before; the Controller layer however will use the REQUIRES_NEW propagation to ensure that it invokes the underlying Service layer in a transactional context. @Transactional( propagation = Propagation.REQUIRES_NEW ) public class Controller{ ... } @Transactional( propagation = Propagation.MANDATORY ) public class Service{ ... } @Transactional( propagation = Propagation.MANDATORY ) public class DAO{ ... } Spring Testing support for Transactions The TestContext framework provides transaction support Spring enabled tests via the PlatformTransactionManager bean in the application context and the @Transactional annotation. Spring also support various test specific annotations which, used in conjunction with the TestContext framework allow for full control over the transaction configuration: @TransactionConfiguration, @Rollback and @BeforeTransaction/@AfterTransaction. A common usage of the framework and a common requirement of an integration test is to leave the database unchanged after the test method is finished. This can be done by annotating the test class with: @TransactionConfiguration( defaultRollback = true ) @Transactional public class TransactionalIntegrationTest{ ... } Also, note that because Spring uses proxies at runtime to manage transactions, the test class must not be final if it’s annotated with @Transactional. Potential Pitfalls Changing the Isolation level One of the major pitfalls when configuring Spring to work with JPA is that changing the isolation of the transaction semantics will not work – JPA does not support custom isolation levels. This is a limitation of JPA, not Spring; nevertheless changing the @Transactionalisolation property will result in: org.springframework.transaction.InvalidIsolationLevelException: Standard JPA does not support custom isolation levels – use a special JpaDialect for your JPA implementation Read Only Transactions The readOnly flag usually generates confusion, especially when working with JPA; from the javadoc: This just serves as a hint for the actual transaction subsystem; it will not necessarily cause failure of write access attempts. A transaction manager which cannot interpret the read-only hint will not throw an exception when asked for a read-only transaction. The fact is that it cannot be guaranteed that an insert or update will not occur when the readOnly flag is set – its behavior is vendor dependent whereas JPA is vendor agnostic. It is also important to understand that the readOnly flag is only relevant inside a transaction; if an operation occurs outside of a transactional context, the flag is simply ignored. A simple example of that would calling a method annotated with: @Transactional( propagation = Propagation.SUPPORTS,readOnly = true ) from a non-transactional context – a transaction will not be created and the readOnly flag will be ignored. Transaction Logging Transactional related issues can also be better understood by fine-tuning logging in the transactional packages; the relevant package in Spring is “org.springframework.transaction”, which should be configured with a logging level of TRACE. Configuring transactions with AOP In addition to annotations, the declarative transactional configuration can of course make use of the aspect-oriented programming support in Spring. As this is not meant to be an exhaustive guide to all the possible ways to configure transactions in Spring, check out the reference for a in depth discussion on using AOP to configure transactions. This is a quick starting point to configuring transactions with AOP: Conclusion This article covered the configuration of the transactional strategies with Spring 3.1 and JPA, using both XML and Java based configuration. Two transaction strategies were discussed, focusing on different ways to manage transaction propagation between the layers of an application. The Spring support for transactional testing as well as some common JPA pitfalls were also discussed. You can check out the full implementation in the github project. From the originalTransaction configuration with JPA and Spring 3.1 of the Persistence with Spring series

this is a super basic and easy question, but i found quite often people asking me how to add an existing project to a tfs team project. it turns out that there are more than one way of doing this, but i usually suggests this simple path that is quite simple and is understandable from people that comes from the subversion world. first of all be sure that you have a valid workspace in your computer that maps the folder in the team project where you want to put your existing project and issue a getlatest . if the team project is new you can simply create a workspace going to menu file –> source control –> workspaces, press add and create a workspace that maps the source to a folder on your pc. figure 1: creating a workspace that maps the whole folder of the source control. now simply go to the local folder and move the existing solution from the original location to the mapped folder, then go to the team explorer –> source control and manually add all the files to tfs source control. in figure2 i represented the process to accomplish this task, first of all select source control, press the add button then visual studio presents you all the files that are in your local folder but are not present in the source control (they are the candidate to be added to the source control). figure 2: adding existing file to source control now you are presented with a list of all the files that will be added to tfs source control, as seen in figure 3 figure 3: list of files that gets added to the source control. as you can see some of the files are excluded (22 in figure 3), this happens because visual studio already knows that certain types of file should be excluded from source control, like all the bin and debug folders and all *.dll files . if you have some lib folder where you store third party library, you can go to the excluded items tab in figure 3 to add manually all the excluded files you want to be added to the source control. since this window is usually cluttered with all the bin and obj directory, i found simpler to: 1) in a first pass add all the file suggested by visual studio 2) browse to lib directory (or whatever folder contains third party library) and add explicitly all the files in the directory. now all files were in pending-add, this means that they will be sent to the source control with a check-in, but before the check-in phase you should open solution file from the source control explorer windows. after the solution is opened visual studio should tell you that this solution is in a source control monitored folder, but source control is not enabled this basically means that, source files are correctly linked to the source control system, but the visual studio integration is not enabled, you can simply press yes and let visual studio actually do binding between projects and source control . if the binding does not happens automatically you will get the windows of figure 4, (you can always open this windows with the menu file –> source control –> change source control. in this window you can simply select one project at a time and press the bind button to perform the bind, until all the project files are in connected status. figure 4: binding windows where you can bind solution and projects file to tfs now you can check-in everything and usually you should create another workspace or ask to another member of the team to do a get-latest of the just-inserted solution, to verify that all the needed files were correctly added to the source control. gian maria. source: http://www.codewrecks.com/blog/index.php/2012/01/27/add-existing-project-to-tfs

Last time we have learnt the basics of WADL. The language itself is not as interesting to write a separate article about it, but the title of this article reveals why we needed that knowledge. Many implementations of JSR 311: JAX-RS: The Java API for RESTful Web Services provide runtime WADL generation out-of-the-box: Apache CXF, Jersey and Restlet. RESTeasy still waiting. Basically these frameworks examine Java code with JSR-311 annotations and generate WADL document available under some URL. Unfortunately Spring MVC not only does not implement the JSR-311 standard (see: Does Spring MVC support JSR 311 annotations?), but it also does not generate WADL for us (see: SPR-8705), even though it is perfectly suited for exposing REST services. For various reasons I started developing server-side REST services with Spring MVC and after a while (say, thirdy resources later) I started to get a bit lost. I really needed a way to catalogue and document all available resources and operations. WADL seemed like a great choice. Fortunately Spring framework is open for extension and it is easy to add new features based on existing infrastructure if you are willing to dig through the code for a while. In order to generate WADL I needed a list of URIs that an application handles, what HTTP methods are implemented and – ideally – which Java method handles each one of them. Obviously Spring does that job already somewhere during boot-strapping MVC DispatcherServlet - scanning for @Controller, @RequestMapping, @PathVariable, etc. - so it seems smart to reuse that information rather then performing the job again. Guess what, it looks like all the information we need is kept in an oddly named RequestMappingHandlerMapping class. Here is a debugger screenshot just to give you an overview how rich information is available: But it gets even better: RequestMappingHandlerMapping is actually a Spring bean which you can easily inject and use: @Controller class WadlController @Autowired()(mapping: RequestMappingHandlerMapping) { @RequestMapping(method = Array(GET)) @ResponseBody def generate(request: HttpServletRequest) = new WadlApplication() } That's right, we will use yet another Spring MVC controller to generate WADL document. Last time we managed to generate JAXB classes representing WADL document (after all WADL is an XML file) so by returning empty instance of WadlApplication we are actually returning empty, but valid WADL: I won't explain the details of the implementation (full source code is available including sample application). It was basically a matter of rewriting Spring models to WADL classes. If you are interested, have a look at WadlGenerator.scala that is a central point of the solution and test cases. Here is one of them: test("should add parameter info for template parameter in URL") { given("") val mapping = Map( mappingInfo("/books", GET) -> handlerMethod("listBooks"), mappingInfo("/books/{bookId}", GET) -> handlerMethod("readBook") ) when("") val wadl = generate(mapping) then("") assertXMLEqual(wadlHeader + """ """ + wadlFooter, wadl) } Unfortunately I was too lazy to correctly name given/when/then blocks. But tests should be pretty readable. The only technical difficulty I would like to mention was translating flat URI patterns provided by Spring infrastructure to hierarchical WADL objects (basically a tree). Here is a simplified version of this problem: having a list of URI patterns as follows: /books /books/{bookId} /books/{bookId}/reviews /books/best-sellers /readers /readers/{readerId} /readers/{readerId}/account/new-password /readers/active /readers/passive Generate the following tree data structure: Of course the data structure is as simple as a Node object holding a label and a children list of Nodes. Not really that challenging, but probably an interesting CodeKata. So what is it all about with this WADL? Is the XML really more readable and helps in managing REST-heavy applications? I wouldn't even bother playing with it if not the great soapUI support for WADL. The WADL generated for an example application I pushed as well can be easily imported to soapUI: Two features are worth mentioning. First of all soapUI displays a tree of REST resources (as opposed to flat list of operations when WSDL is imported). Next to every HTTP method there is a corresponding Java method that handles it (this can be disabled) for troubleshooting and debugging purposes. Secondly, we can pick any HTTP method/resource and invoke it. Based on WADL description soapUI will create user-friendly wizard where one can input parameters. Default values are automatically populated. When we are done, the application will generate HTTP request with correct URL and content, displaying the response when it arrives. Really helpful! By the way have you noticed the max and page query parameters? Our small library uses reflection to find @RequestParam annotations so e.g. the following controller: @Controller @RequestMapping(value = Array("/book/{bookId}/review")) class ReviewController @Autowired()(reviewService: ReviewService) { @RequestMapping(method = Array(GET)) @ResponseBody def listReviews( @RequestParam(value = "page", required = false, defaultValue = "1") page: Int, @RequestParam(value = "max", required = false, defaultValue = "20") max: Int) = new ResultPage(reviewService.listReviews(new PageRequest(page - 1, max))) //... } will be translated into WADL-compatible description: ? Hope you had fun with this small library I have written. Feel free to include it in your project and don't hesitate to report bugs. Full source code under Apache license is available on GitHub: https://github.com/nurkiewicz/spring-rest-wadl. From http://nurkiewicz.blogspot.com/2012/02/automatically-generating-wadl-in-spring.html

XML is for dinosaurs, right? Everybody uses JSON these days. So you do, don’t you? But what about things like XSD, XSLT, JAXB, XPath, etc – is it all evil? In this article, I’d like to introduce the StAXON project (APL2) which tries to give you the best from both worlds: JSON outside, but XML inside. One benefit from this is that you can integrate JSON with powerful XML-related technologies for free. StAXON lets you read and write JSON using the Java Streaming API for XML (javax.xml.stream), also known as StAX. More specifically, StAXON provides implementations of the StAX Cursor API (XMLStreamReader and XMLStreamWriter) StAX Event API (XMLEventReader and XMLEventWriter) StAX Factory API (XMLInputFactory and XMLOutputFactory) for JSON. You may know the Jettison project, which also has XMLStreamReader and XMLStreamWriter implementations. However, StAXON aims to provide a more comprehensive and consistent solution and tries to avoid some of the issues users are having with Jettison. Anyway, let’s get started and see what this “anti-aging substance” for XML can do. Setup Add the following dependency to your Maven POM file: de.odysseus.staxon staxon 1.0 or get the latest StAXON JAR from the Downloads page and add it to your classpath. Mapping Convention The purpose of StAXON’s mapping convention is to generate a more compact JSON. It borrows the "$" syntax for text elements from the Badgerfish convention but attempts to avoid needless text-only JSON objects: Element names become object properties: <–> {"alice":null} Attributes go in properties whose name begin with "@": <–> {"alice":{"@charlie":"david"} Text-only elements go to a simple key/value property: bob <–> {"alice":"bob"} Otherwise, text content is mapped to the "$" property: bob <–> {"alice":{"@charlie":"david","$":"bob"} Nested elements go to nested properties: charlie <–> {"alice":{"bob":"charlie"} A default namespace declaration goes in the element’s "@xmlns" property: <–> {"alice":{"@xmlns":"http://foo.com"} A prefixed namespace declaration goes in the element’s "@xmlns:" property: John Doe555-1111 However, with our JSON-based writer, the output is {"customer":{"name":"John Doe","phone":"555-1111"} Reading JSON Create a JSON-based reader: String json = "{\"customer\":{\"name\":\"John Doe\",\"phone\":\"555-1111\"}"; XMLInputFactory factory = new JsonXMLInputFactory(); XMLStreamReader reader = factory.createXMLStreamReader(new StringReader(json)); Read your document: assert reader.getEventType() == XMLStreamConstants.START_DOCUMENT; reader.nextTag(); assert reader.isStartElement() && "customer".equals(reader.getLocalName()); reader.next(); assert reader.isStartElement() && "name".equals(reader.getLocalName()); reader.next(); assert reader.hasText() && "John Doe".equals(reader.getText()); reader.nextTag(); assert reader.isEndElement(); reader.next(); assert reader.isStartElement() && "phone".equals(reader.getLocalName()); reader.next(); assert reader.hasText() && "555-111".equals(reader.getText()); reader.nextTag(); assert reader.isEndElement(); reader.next(); assert reader.isEndElement(); reader.next(); assert reader.getEventType() == XMLStreamConstants.END_DOCUMENT; reader.close(); Factory Configuration The JsonXMLInputFactory and JsonXMLOutputFactory classes can be configured via the standard setProperty(String, Object) API. The factory classes define several constants for properties they support. However, the JsonXMLConfig interface provides a convenient way to hold the configuration of both - input and output - factories: JsonXMLConfig config = new JsonXMLConfigBuilder(). virtualRoot("customer"). prettyPrint(true). build(); XMLInputFactory inputFactory = new JsonXMLInputFactory(config); ... XMLOutputFactory outputFactory = new JsonXMLOutputFactory(config); ... Virtual Roots Set the virtualRoot configuration property to strip the root element from the JSON representation, e.g. { "name" : "John Doe", "phone" : "555-1111" } As XML requires a single root element, but JSON documents often don’t have one, this is an important feature required to read and write existing JSON formats. Mastering Arrays What about JSON arrays? Unfortunately, there’s nothing like this in XML. And to be honest, this causes most of the trouble when writing JSON via an XML API like StAX. Simply omitting the array boundaries would lead to non-unique JSON properties, which is usually not desired. StAXON provides several ways to deal with JSON arrays. At the core is the idea to leverage XML processing instructions to tell the writer about to start an array: the processing instruction maps a sequence of XML elements with the same name to a JSON array. The processing instruction optionally takes the array element tag name (with prefix) as data. There’s no end array hint as StAXON detects the end of an array sequence and closes it automatically. Consider the following JSON document: { "alice" : { "bob" : [ "edgar", "charlie" ], "peter" : null } } In order to get a "bob" array instead of two separate "bob" properties, we need to provide XML events corresponding to edgar charlie I.e., with the cursor API, you would just insert writer.writeProcessingInstruction(JsonXMLStreamConstants.MULTIPLE_PI_TARGET); // to start an array. Initiating Arrays with Element Paths Sometimes it is not desired or even impossible to generate processing instruction to control arrays. This may be the case if the actual writing isn’t done by your code, but some other framework like JAXB or similar, and you only provide a stream writer. Addressing such a scenario, wouldn’t it be nice being able to tell the writer beforehand, which elements should trigger a JSON array? This is where the XMLMultipleStreamWriter and XMLMultipleEventWriter wrappers step in. E.g., to specify a sequence of bob elements below root element alice as a multiple path: writer = new XMLMultipleStreamWriter(writer, true, "/alice/bob"); The boolean parameter specifies whether our paths include the root node (alice) from the paths. That is, we could also use writer = new XMLMultipleStreamWriter(writer, false, "/bob"); To wrap all bob fields into arrays (not just alice children), we can use a relative path, without a leading slash: writer = new XMLMultipleStreamWriter(writer, false, "bob"); Now we (or some legacy code, framework, …) may write our document, and the writer will take care to trigger the bob array for us. Triggering Arrays automatically Finally, if nothing else works for you, you may also let StAXON fully automatically determine array boundaries. Use this only if you cannot provide processing instructions and cannot provide the paths of the elements that should be wrapped into JSON arrays. However, using this method has several drawbacks: The writer basically needs to cache the entire document in memory, eating both space and time. The writer will not be able to produce empty arrays or arrays with a single element. To enable this feature, set the JsonXMLOutputFactory.PROP_AUTO_ARRAY property to true. Triggering Document Arrays StAXON’s writer implementation allows you to wrap a sequence of documents into a JSON array. To do this, write the PI before writing anything else: writer.writeProcessingInstruction(JsonXMLStreamConstants.MULTIPLE_PI_TARGET); writer.writeStartDocument(); // first array component ... writer.writeEndDocument(); writer.writeStartDocument(); // second array component ... writer.writeEndDocument(); ... writer.close(); The writer.close() call is crucial here, as it will close the JSON array. Using JAXB Consider a JAXB-annotated Customer class: @JsonXML(virtualRoot = true, prettyPrint = true, multiplePaths = "phone") @XmlRootElement public class Customer { public String name; public List phone; } The @JsonXML annotation is used to configure the mapping details. In the above example, the customer root element is stripped from the JSON representation, phone elements are wrapped into an array and JSON output is nicely formatted, e.g. { "name" : "John Doe", "phone" : [ "555-1111" ] } Now, the JsonXMLMapper class enables for dead-simple mapping to and from JSON: /* * Create mapper instance. */ JsonXMLMapper mapper = new JsonXMLMapper(Customer.class); /* * Read customer. */ InputStream input = getClass().getResourceAsStream("input.json"); Customer customer = mapper.readObject(input); input.close(); /* * Write back to console */ mapper.writeObject(System.out, customer); Using JAX-RS StAXON provides the staxon-jaxrs module, which enables your RESTful services to serialize/deserialize JAXB-annotated classes to/from JSON. It includes the following JAX-RS @Provider classes: de.odysseus.staxon.json.jaxrs.jaxb.JsonXMLObjectProvider is used to read and write JSON objects de.odysseus.staxon.json.jaxrs.jaxb.JsonXMLArrayProvider is used to read and write JSON arrays In order to select the StAXON message body readers/writers for your resource, a @JsonXML annotation is required. When used with JAX-RS, the @JsonXML annotation can be placed on a model type (@XmlRootElement or @XmlType) to configure its serialization and deserialization a JAX-RS resource method to configure serialization of the result type a parameter of a JAX-RS resource method to configure deserialization of the parameter type If a @JsonXML annotation is present at a model type and a resource method or parameter, the latter will override the model type annotation. If neither is present, StAXON will not handle the resource. You can find a sample project using Jersey with StAXON here. Using XPath XPath is another standard that can be easily adopted for use with JSON. The Java XPath API (javax.xml.xpath) doesn’t let us provide an XMLStreamReader or similar as a source, but requires a Document Object Model (DOM). Therefore, we need to read our JSON into a DOM first to apply expressions against that DOM. This could be done by performing an XSLT identity transformation to a DOMResult. However, StAXON provides the DOMEventConsumer class to translate XML events to DOM nodes, which should be faster and simpler than leveraging XSLT. Once we have a DOM, there’s nothing special with applying XPath expressions. StringReader json = new StringReader("{\"edgar\":\"david\",\"bob\":\"charlie\"}"); /* * Our sample JSON has no root element, so specify "alice" as virtual root */ JsonXMLConfig config = new JsonXMLConfigBuilder().virtualRoot("alice").build(); /* * create event reader */ XMLEventReader reader = new JsonXMLInputFactory(config).createXMLEventReader(json); /* * parse JSON into Document Object Model (DOM) */ Document document = DOMEventConsumer.consume(reader); /* * evaluate an XPath expression */ XPath xpath = XPathFactory.newInstance().newXPath(); System.out.println(xpath.evaluate("//alice/bob", document)); Running the above sample will print charlie to the console. What else? In the end, using an XML API to read and write JSON may still look like a compromise, but it may turn out to be a good choice. The availability of a StAX implementation for JSON acts as a door opener to powerful XML related technologies and easily enables for dual-format (XML and JSON) services. There’s more we can do with StAXON: XSD, XSLT, XQuery, XML-JSON/JSON-XML conversions, to name a few. Please check the Wiki for some of those.

Even in languages where there are no constructs but classes, there is no constraint that can force a programmer into writing object-oriented code. In many cases, just wrapping a series of functions into classes do not result in the design. The Convert Procedural Design to Objects has great benefits, but it reaches a very large scale (potentially the whole application). What does object-oriented mean? In 2011, there is no reason to write procedural code anymore in a web application: all libraries and frameworks worth inclusion are object-oriented, even a part of the PHP code (SPL but most importantly PDO, and even DateTime). All other successful languages in the web space are either object-oriented, functional, or both. Software design literature is based on objects and their patterns. However, using class and extends keywords does not suffice to produce an object-oriented design; entire books are written on this topic. This refactoring tries to solve a common case of procedural design shoehorned into an object model: classes containing behavior, and depending on many other ones. dumb classes only being a container for data, or worse primitive types with no methods at all. It is common in procedural design to segregate responsibilities in this procedure/record pattern, but high level methods can be added on these dumb classes to encapsulate a bit of the data they are containing, and simplify the procedural classes using them. It is just a starting point towards "object-orientation", but often an overlooked one. The Tell Don't Ask principle summarizes what we would like to do in very few words: Procedural code gets information then makes decisions. Object-oriented code tells objects to do things. -- Alec Sharp Instead of an infinite series of calls from a procedure to getters and setters, we want to pass messages even to the lower level objects. Steps A preliminary step is to turn primitive data structures into a data object wrapping them and providing getters. If you see variables like arrays or strings passed around in the code to refactor, this step is necessary to provide a class to accomodate potential new methods. Inline the procedural code into a single class. This step makes us able to extract code along different lines than the original ones in the rest of the refactoring: for example, procedural code is often divided in temporal steps, while objects may segregate different parts of the available data instead. Extract methods on the procedural class. See the next steps for hints on what to extract. Methods that have one of the dumb objects as argument can be moved on the object itself, by eliminating it as a parameter but maintaining the remaining ones. Move Method should free the original giant class from any unrelated responsibilities. The goal is to remove logic from the procedural class as much as possibile, going into an opposite direction with regard to the original design; Fowler notes that in some cases the procedural class totally disappears. Example One of my popular examples is invoice calculation: the computation of fields like total price and due taxes from a series of information. In this procedural design, we have one invoice and a bunch of rows modelled with Primitive Obsession (as arrays). assertEquals(4640, $invoice->total()); } } class Invoice { private $rows; public function __construct($rows) { $this->rows = $rows; } public function total() { $total = 0; foreach ($this->rows as $row) { $rowTotal = $row[0] + $row[0] * $row[1] / 100; $total += $rowTotal; } return $total; } } We introduce the Row class, but the design is now worse: it adds a bunch of lines of code (the new class) without the new entity giving us something in return. The Row object has no responsibilities, and we just have to write getters and sometimes setters. At least we're writing down parts of our model for documentation (giving names to the net price and tax rate numbers), but we aren't sure this model is the most versatile one. assertEquals(4640, $invoice->total()); } } class Invoice { private $rows; public function __construct($rows) { $this->rows = $rows; } public function total() { $total = 0; foreach ($this->rows as $row) { $rowTotal = $row->getNetPrice() + $row->getTaxRate() * $row->getNetPrice() / 100; $total += $rowTotal; } return $total; } } class Row { public function __construct($netPrice, $taxRate) { $this->netPrice = $netPrice; $this->taxRate = $taxRate; } public function getNetPrice() { return $this->netPrice; } public function getTaxRate() { return $this->taxRate; } } For the scope of this small example all business logic is already in a single class, thus we don't have to inline anything. Let's extract a first method instead: class Invoice { private $rows; public function __construct($rows) { $this->rows = $rows; } public function total() { $total = 0; foreach ($this->rows as $row) { $total += $this->rowTotal($row); } return $total; } public function rowTotal($row) { return $row->getNetPrice() + $row->getTaxRate() * $row->getNetPrice() / 100; } } That was a small enough step. In a real situation, the extracted code may be 100-line long, so we would want to test the extraction has been successful before doing anything else. In fact, since the test still passes, we can notice this method has a Row object in its arguments, so it can be moved on Row now that its logic has been clearly isolated: $this->field references should become additional parameters of the method before moving it. Other parameters should just remain formal parameters. Calls to $this->anotherMethod() would be more difficult to treat, as you have the options of moving anothetMethod() in the Row class too, or to extract an interface containing anotherMethod() and pass $this. While moving the code, we change the references to $row to $this, and check that the method scope is public. We also rename the method to total() instead of rowTotal(). { private $rows; public function __construct($rows) { $this->rows = $rows; } public function total() { $total = 0; foreach ($this->rows as $row) { $total += $row->total(); } return $total; } } class Row { public function __construct($netPrice, $taxRate) { $this->netPrice = $netPrice; $this->taxRate = $taxRate; } public function getNetPrice() { return $this->netPrice; } public function getTaxRate() { return $this->taxRate; } public function total() { return $this->getNetPrice() + $this->getTaxRate() * $this->getNetPrice() / 100; } } Finally, we inline the getters, since they're not used from outside the Row class. They will be introduced again in the future in case there is a real need for them: as a rule of thumb we avoid exposing any state from Row that is not necessary. class Row { public function __construct($netPrice, $taxRate) { $this->netPrice = $netPrice; $this->taxRate = $taxRate; } public function total() { return $this->netPrice + $this->taxRate * $this->netPrice / 100; } }

I recently spent some time learning JavaFX and doing a custom control is a good practice to dive a little bit deeper into the concepts of a new gui library. Having some background in financial software I did of course miss the equivalent of a JFormattedTextField and a JSpinner control in the current 2.0 release. So going down that road seemed like a good choice to me. And here are my controls: a NumberTextField, that can be configured with an arbitrary NumberFormat a Spinner field that also can also be configured with an arbitrary NumberFormat and controlled with the arrow keys or arrow buttons, that are part of the control The controls and an example can be downloaded as a netbeans project.The example also includes a css file that styles the spinner with either straight or rounded corners. NumberTextField The NumberTextField was pretty easy and I wouldn't even consider this a custom control as I only changed the behaviour of an already existing control. It extends a normal TextField, adds a NumberProperty that serves as the model and holds a BigDecimal (for financial applications we need exact types) and does some formatting and parsing.That's it, no big deal. package de.thomasbolz.javafx; import java.math.BigDecimal; import java.text.NumberFormat; import java.text.ParseException; import javafx.beans.property.ObjectProperty; import javafx.beans.property.SimpleObjectProperty; import javafx.beans.value.ChangeListener; import javafx.beans.value.ObservableValue; import javafx.event.ActionEvent; import javafx.event.EventHandler; import javafx.scene.control.TextField; /** * Textfield implementation that accepts formatted number and stores them in a * BigDecimal property The user input is formatted when the focus is lost or the * user hits RETURN. * * @author Thomas Bolz */ public class NumberTextField extends TextField { private final NumberFormat nf; private ObjectProperty number = new SimpleObjectProperty<>(); public final BigDecimal getNumber() { return number.get(); } public final void setNumber(BigDecimal value) { number.set(value); } public ObjectProperty numberProperty() { return number; } public NumberTextField() { this(BigDecimal.ZERO); } public NumberTextField(BigDecimal value) { this(value, NumberFormat.getInstance()); initHandlers(); } public NumberTextField(BigDecimal value, NumberFormat nf) { super(); this.nf = nf; initHandlers(); setNumber(value); } private void initHandlers() { // try to parse when focus is lost or RETURN is hit setOnAction(new EventHandler() { @Override public void handle(ActionEvent arg0) { parseAndFormatInput(); } }); focusedProperty().addListener(new ChangeListener() { @Override public void changed(ObservableValue observable, Boolean oldValue, Boolean newValue) { if (!newValue.booleanValue()) { parseAndFormatInput(); } } }); // Set text in field if BigDecimal property is changed from outside. numberProperty().addListener(new ChangeListener() { @Override public void changed(ObservableValue obserable, BigDecimal oldValue, BigDecimal newValue) { setText(nf.format(newValue)); } }); } /** * Tries to parse the user input to a number according to the provided * NumberFormat */ private void parseAndFormatInput() { try { String input = getText(); if (input == null || input.length() == 0) { return; } Number parsedNumber = nf.parse(input); BigDecimal newValue = new BigDecimal(parsedNumber.toString()); setNumber(newValue); selectAll(); } catch (ParseException ex) { // If parsing fails keep old number setText(nf.format(number.get())); } } } NumberSpinner The NumberSpinner is only slightly more complicated. It builds upon the NumberTextField and adds an increment and decrement button, that increments and decrements the value in the field by a stepwidth. Initial value, stepwidth and underlying NumberFormat are set in the constructor. The textfield and the size of the buttons are scaled according to the font size that can be - for example - set in the .css file. package de.thomasbolz.javafx; import java.math.BigDecimal; import java.text.NumberFormat; import javafx.beans.binding.NumberBinding; import javafx.beans.property.ObjectProperty; import javafx.beans.property.SimpleObjectProperty; import javafx.event.ActionEvent; import javafx.event.EventHandler; import javafx.geometry.Pos; import javafx.scene.control.Button; import javafx.scene.input.KeyCode; import javafx.scene.input.KeyEvent; import javafx.scene.layout.HBox; import javafx.scene.layout.StackPane; import javafx.scene.layout.VBox; import javafx.scene.shape.LineTo; import javafx.scene.shape.MoveTo; import javafx.scene.shape.Path; import javax.swing.JSpinner; /** * JavaFX Control that behaves like a {@link JSpinner} known in Swing. The * number in the textfield can be incremented or decremented by a configurable * stepWidth using the arrow buttons in the control or the up and down arrow * keys. * * @author Thomas Bolz */ public class NumberSpinner extends HBox { public static final String ARROW = "NumberSpinnerArrow"; public static final String NUMBER_FIELD = "NumberField"; public static final String NUMBER_SPINNER = "NumberSpinner"; public static final String SPINNER_BUTTON_UP = "SpinnerButtonUp"; public static final String SPINNER_BUTTON_DOWN = "SpinnerButtonDown"; private final String BUTTONS_BOX = "ButtonsBox"; private NumberTextField numberField; private ObjectProperty stepWitdhProperty = new SimpleObjectProperty<>(); private final double ARROW_SIZE = 4; private final Button incrementButton; private final Button decrementButton; private final NumberBinding buttonHeight; private final NumberBinding spacing; public NumberSpinner() { this(BigDecimal.ZERO, BigDecimal.ONE); } public NumberSpinner(BigDecimal value, BigDecimal stepWidth) { this(value, stepWidth, NumberFormat.getInstance()); } public NumberSpinner(BigDecimal value, BigDecimal stepWidth, NumberFormat nf) { super(); this.setId(NUMBER_SPINNER); this.stepWitdhProperty.set(stepWidth); // TextField numberField = new NumberTextField(value, nf); numberField.setId(NUMBER_FIELD); // Enable arrow keys for dec/inc numberField.addEventFilter(KeyEvent.KEY_PRESSED, new EventHandler() { @Override public void handle(KeyEvent keyEvent) { if (keyEvent.getCode() == KeyCode.DOWN) { decrement(); keyEvent.consume(); } if (keyEvent.getCode() == KeyCode.UP) { increment(); keyEvent.consume(); } } }); // Painting the up and down arrows Path arrowUp = new Path(); arrowUp.setId(ARROW); arrowUp.getElements().addAll(new MoveTo(-ARROW_SIZE, 0), new LineTo(ARROW_SIZE, 0), new LineTo(0, -ARROW_SIZE), new LineTo(-ARROW_SIZE, 0)); // mouse clicks should be forwarded to the underlying button arrowUp.setMouseTransparent(true); Path arrowDown = new Path(); arrowDown.setId(ARROW); arrowDown.getElements().addAll(new MoveTo(-ARROW_SIZE, 0), new LineTo(ARROW_SIZE, 0), new LineTo(0, ARROW_SIZE), new LineTo(-ARROW_SIZE, 0)); arrowDown.setMouseTransparent(true); // the spinner buttons scale with the textfield size // TODO: the following approach leads to the desired result, but it is // not fully understood why and obviously it is not quite elegant buttonHeight = numberField.heightProperty().subtract(3).divide(2); // give unused space in the buttons VBox to the incrementBUtton spacing = numberField.heightProperty().subtract(2).subtract(buttonHeight.multiply(2)); // inc/dec buttons VBox buttons = new VBox(); buttons.setId(BUTTONS_BOX); incrementButton = new Button(); incrementButton.setId(SPINNER_BUTTON_UP); incrementButton.prefWidthProperty().bind(numberField.heightProperty()); incrementButton.minWidthProperty().bind(numberField.heightProperty()); incrementButton.maxHeightProperty().bind(buttonHeight.add(spacing)); incrementButton.prefHeightProperty().bind(buttonHeight.add(spacing)); incrementButton.minHeightProperty().bind(buttonHeight.add(spacing)); incrementButton.setFocusTraversable(false); incrementButton.setOnAction(new EventHandler() { @Override public void handle(ActionEvent ae) { increment(); ae.consume(); } }); // Paint arrow path on button using a StackPane StackPane incPane = new StackPane(); incPane.getChildren().addAll(incrementButton, arrowUp); incPane.setAlignment(Pos.CENTER); decrementButton = new Button(); decrementButton.setId(SPINNER_BUTTON_DOWN); decrementButton.prefWidthProperty().bind(numberField.heightProperty()); decrementButton.minWidthProperty().bind(numberField.heightProperty()); decrementButton.maxHeightProperty().bind(buttonHeight); decrementButton.prefHeightProperty().bind(buttonHeight); decrementButton.minHeightProperty().bind(buttonHeight); decrementButton.setFocusTraversable(false); decrementButton.setOnAction(new EventHandler() { @Override public void handle(ActionEvent ae) { decrement(); ae.consume(); } }); StackPane decPane = new StackPane(); decPane.getChildren().addAll(decrementButton, arrowDown); decPane.setAlignment(Pos.CENTER); buttons.getChildren().addAll(incPane, decPane); this.getChildren().addAll(numberField, buttons); } /** * increment number value by stepWidth */ private void increment() { BigDecimal value = numberField.getNumber(); value = value.add(stepWitdhProperty.get()); numberField.setNumber(value); } /** * decrement number value by stepWidth */ private void decrement() { BigDecimal value = numberField.getNumber(); value = value.subtract(stepWitdhProperty.get()); numberField.setNumber(value); } public final void setNumber(BigDecimal value) { numberField.setNumber(value); } public ObjectProperty numberProperty() { return numberField.numberProperty(); } public final BigDecimal getNumber() { return numberField.getNumber(); } // debugging layout bounds public void dumpSizes() { System.out.println("numberField (layout)=" + numberField.getLayoutBounds()); System.out.println("buttonInc (layout)=" + incrementButton.getLayoutBounds()); System.out.println("buttonDec (layout)=" + decrementButton.getLayoutBounds()); System.out.println("binding=" + buttonHeight.toString()); System.out.println("spacing=" + spacing.toString()); } } number_spinner.css Last but not least the control can be styled in the css file. I played around with two looks, rounded corners and straight corners (see attached screenshots). You can switch between them by changing the border/background-radiuses in #NumberField, #ButtonBox, #SpinnerButtonUp and #SpinnerButtonDown. .root{ -fx-font-size: 24pt; /* -fx-base: rgb(255,0,0);*/ /* -fx-background: rgb(50,50,50);*/ } #NumberField { -fx-border-width: 1; -fx-border-color: lightgray; -fx-background-insets:1; -fx-border-radius:3 0 0 3; /* -fx-border-radius:0 0 0 0;*/ } #NumberSpinnerArrow { -fx-fill: gray; -fx-stroke: gray; /* -fx-effect: innershadow( gaussian , black , 2 , 0.6 , 1 , 1 )*/ } #ButtonsBox { -fx-border-color:lightgray; -fx-border-width: 1 1 1 0; -fx-border-radius: 0 3 3 0; /* -fx-border-radius: 0 0 0 0;*/ } #SpinnerButtonUp { -fx-background-insets: 0; -fx-background-radius:0 3 0 0; /* -fx-background-radius:0;*/ } #SpinnerButtonDown { -fx-background-insets: 0; -fx-background-radius:0 0 3 0; /* -fx-background-radius:0;*/ } Conclusion Doing custom controls in JavaFX is really no big deal although the examples above are really easy ones. JavaFX being a pure Java API since 2.0 now integrates even better than before with languages like groovy where BigDecimal is a first class citizen. This makes it an almost perfect couple for financial desktops applications.

Execute the slow integration tests separately from unit tests and show as much information about them as possible in Sonar.

Prefix encoding, sometimes called front encoding, is yet another algorithm that tries to remove duplicated data in order to reduce its size. Its principles are simple, however this algorithm tends to be difficult to implement. To understand why, first let’s take a look at its nature. Have a look on the following dictionary. use used useful usefulness uselss uselessly uselessness Instead of keeping all these words in plain text or transferring all them over a network, we can compress (encode) them with prefix encoding. It’s clear that each of these words begins with the prefix “use” which is also the first word from the list. So we can easily compress them into the following array. $data = array( 0 => 'use', 1 => '0d', 2 => '0ful', 3 => '0fully', 4 => '0less', 5 => '0lessly', 6 => '0lessness', ); It’s clear that this is not the best compression and we can go even further by using not only the first word as prefix. $data = array( 0 => 'use', 1 => '0d', 2 => '0ful', 3 => '2ly', 4 => '0less', 5 => '4ly', 6 => '4ness', ); Now the compression is better and the good news is that decompression is a fairly simple process. However the tricky part is compression itself. The problem is that it is quite difficult to chose an appropriate prefix. In our first example this is simple, but most of the time in practice we will have more heterogeneous data. Indeed the process of compression can be very difficult for randomly generated data and the algorithm will be not only slow, but difficult to implement. The good thing is that this algorithm can be used in many cases once we know the data format in advance. So let’s see three examples where this algorithm can be very handy. Application Here are three examples of prefix encoding. As I stated above, the process of compression can be very difficult for random data, so it is a good practice to use it only if you know in advance the format of the input data. Date and time prefixes We humans often skip the first two digits of a year, so for instance we don’t always write 1995 or 1996, but we use the shorter – ‘95 and ‘96. Thus years can be encoded with shorter strings. input: (1991, 1992, 1993, 1994, 1995, 1996 output: (91, 92, 93, 94, 95, 96) The problem is that with small changes of the input stream we can confuse the decoder. Thus if we add years from the 21st century we lose the uniqueness of the data. input: (1998, 1992, 1999, 2011, 2012) output: (98, 92, 99, 11, 12) Now the decoder can decode the last two values as (1911, 1912) as “19” is considered to be the prefix. So we must know in advance that our prefix is absolutely equal for each of the values. If not the encoding format must be different. For instance we can also encode the prefix, with some special marker. input: (1998, 1992, 1932, 1924, 2001, 2012) output: (#19, 98, 92, 32, 24, #20, 01, 12) Once the decoder reads the # character it will know to decode the following number as prefix. This can be used in practice for date and time formats. Let’s say we have some datetime values, but we know that all of them are in the same day. 2012-01-31 15:33:45 2012-01-31 16:12:11 2012-01-31 17:32:35 2012-01-31 18:54:34 Obviously we can omit the date part of these strings and send (keep) only the time. Once again, we must be absolutely sure that all these values are in the same day. If not, we can use the encoding strategy of the previous example. Phone numbers Phone numbers are the typical case of prefix encoding. Not only the international code, but also the mobile network operators use prefixes for their phone numbers. Thus if we have to transfer phone numbers from, let’s say the UK, we can replace the leading “+44” with something shorter. If you happen to code a phone book for a mobile device you can save some space by compressing the data using prefix encoding and thus the user will have more space and will store more phone numbers on his or her mobile device. Phone number prefixes can be also used for database normalization. Thus you can store them in a separate db table and leave only the unique numbers from the phonebook. Geo Coordinates Using the same example from my previous post we can send GEO coordinates by removing a common prefix, for large levels of zoom. Indeed when you need to send lots of markers to your map application you can expect all of these markers to be fairly close to each other in large zoom level. On large zoom levels we can expect markers to have the same prefix. Now the coordinates of those points can have a common prefix, like the example bellow with the Subway stations. LatLon(40.762959,-73.985989) LatLon(40.761886,-73.983629) LatLon(40.762861,-73.981612) LatLon(40.764616,-73.98056) We can see that all of these GEO points have the same prefix (40.76x, -73.98x), so we can send the prefix only once. Prefix: (40.76,-73.98) Data: LatLon(2959,5989) LatLon(1886,3629) LatLon(2861,1612) LatLon(4616,056) These are only three examples of prefix encoding and this algorithm is very useful when transferring homogeneous data. Suffix Encoding Suffix encoding is practically the same algorithm as prefix encoding, with the small difference that we use to encode duplicating suffixes. Like the examples below, suffix encoding can be useful in replacing repeating last name suffixes. Johsnon Clark Jackson Or company names. Apple Inc. Google Inc. Yahoo! Inc. Here we can replace “ Inc.” with something else, but shorter. Related posts: Computer Algorithms: Data Compression with Relative Encoding Computer Algorithms: Data Compression with Run-length Encoding Computer Algorithms: Data Compression with Diagram Encoding and Pattern Substitution Source: http://www.stoimen.com/blog/2012/02/06/computer-algorithms-data-compression-with-prefix-encoding/

The logging in Jersey, the reference JAX-RS implementation, is little sub-optimal. For example if it cannot find a method producing the expected MIME type then it will return “Unsupported mime type” to the client but won’t log anything (which mime type was requested, which mime types are actually available, …). Debugging it isn’t exactly easy either, so what to do? Well, I don’t know the ultimate solution but want to share few tips. Enable Tracing of Request Matching Jersey since version 1.1.5 supports request matching tracing, provided somehow detailed information about the matching process in the response headers. To enable it for the Jersey Test framework you’d do something like this in your test class: public class MyJerseyTest extends JerseyTest { public MyJerseyTest() { super(new WebAppDescriptor .Builder("my.package.with.jaxrs.resources") .contextPath("myCtxPath") .servletPath("/myServletPath") .initParam("com.sun.jersey.config.feature.Trace", "true") .build()); } // Your test methods here ...; you can get the trace headers via ClientResponse#getHeaders() } To enable it for the server itself (though might be not such a good idea to enable this in production), you would set it in web.xml: Jersey REST Service for value codes com.sun.jersey.spi.container.servlet.ServletContainer ... com.sun.jersey.config.feature.Trace true ... The headers, which you can obtain via e.g. curl -i or via ClientResponse#getHeaders(), might look like this: {X-Jersey-Trace-008=[mapped exception to response: javax.ws.rs.WebApplicationException@56f9659d -> 415 (Unsupported Media Type)], X-Jersey-Trace-002=[accept right hand path java.util.regex.Matcher[pattern=/myResource/([-0-9a-zA-Z_]+)(/.*)? region=0,17 lastmatch=/myResource/23/mySubresources]: "/myResource/23/mySubresources" -> "/myResource/23" : "/mySubresources"], X-Jersey-Trace-003=[accept resource: "myResource/23" -> @Path("/myResource/{item: [-0-9a-zA-Z_]+}") com.example.MyExampleResource@41babddb], X-Jersey-Trace-000=[accept root resource classes: "/myResource/23/mySubresources"], X-Jersey-Trace-001=[match path "/myResource/23/mySubresources" -> "/application\.wadl(/.*)?", "/myResource/([-0-9a-zA-Z_]+)(/.*)?", "/myResource(/.*)?", "/mySubresources/([-0-9a-zA-Z_]+)(/.*)?"], X-Jersey-Trace-006=[accept sub-resource methods: "myResource/23" : "/mySubresources", GET -> com.example.MyExampleResource@41babddb], X-Jersey-Trace-007=[accept termination (matching failure): "/mySubresources"], X-Jersey-Trace-004=[match path "/mySubresources" -> "/mySubresources(/)?", ""], X-Jersey-Trace-005=[accept right hand path java.util.regex.Matcher[pattern=/mySubresources(/)? region=0,6 lastmatch=/mySubresources]: "/mySubresources" -> "/mySubresources" : ""] , Transfer-Encoding=[chunked], Date=[Tue, 31 Jan 2012 14:48:26 GMT], server=[grizzly/2.1.2], Content-Type=[text/html; charset=iso-8859-1]} provided that you have the class com.example.MyExampleResource annotated with @Path("/myResource/{item: [-0-9a-zA-Z_]+}") and a method annotated with @GET @Path("mySubresources") (and the class field @PathParam("item") Long item). As you can see, there is still no info regarding accepted/supported MIME types. Get Detailed Logging Into a File Jersey uses Java logging, which is know for being difficult to configure. Here is a dirty trick to get detailed Jersey logs into a file: public class MyJerseyTest extends JerseyTest { @BeforeClass public static void setupJerseyLog() throws Exception { Handler fh = new FileHandler("/tmp/jersey_test.log"); Logger.getLogger("").addHandler(fh); Logger.getLogger("com.sun.jersey").setLevel(Level.FINEST); } // Your test methods here ... } Notice that even thoug the log level is ALL, the logs still might be quite useless to troubleshoot some problems (such s the unsupported MIME type). Configure Request/Response Logging Filters Jersey provides a LoggingFilter that can be used to log request/response entities and it can be installed both into the server and the client. The com.sun.jersey.api.container.filter.LoggingFilter may be installed into the server via init-params, the com.sun.jersey.api.client.filter.LoggingFilter may be installed into the client via client.addFilter. JerseyTest automatically installs the LoggingFilter into the client it uses if the system property “enableLogging” is set (to whatever). From http://theholyjava.wordpress.com/2012/01/31/troubleshooting-jersey-rest-server-and-client/

Last October I wrote a blog entitled Autowiring Property Values into Spring Beans describing how to use Spring’s @Value annotation to inject property values into your beans from both a property file and Java system properties. Last week, I came across this little gotcha whilst helping out on another project.... This project was quite rightly re-using a module written as part of a different project. One of the module's tasks was to process a query string and it had a root url property that could be optionally injected to help with various bits of this processing. The original project that used this module was able to supply the handy root url property, whilst the project that re-used the module couldn’t. This meant that that when the web-server started up an exception similar to the one below was thrown... org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'autowiredFakaSource': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private java.lang.String miscillaneous.property_placeholder.AutowiredFakaSource.optional; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'optional' at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1074) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:291) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) at …. shortened for readability. It turns out that, when autowiring properties using @Value, one of the things that you can’t do is to specify the injected property as optional. This seems like a bit of an over-sight by the Guys at Spring as you can make autowired injected objects optional using: @Autowired(required = false) private MyPojo anotherObject; There are couple of work arounds for this problem. The first is to ensure that your project’s .properties file contains an empty place holder property. For example one of your Spring components contains something like this: @Value("${optional}") private String optionalPropertyValue; ...then your .properties file should contain an empty entry like this: optional= In this case, Spring will inject an empty string into your component and your code should run. The second work around is to make use of the 'default value' functionality. For example, suppose that you wanted to make life easy for the folks that are going to use your application. One of the things you can do is to code in default values for your properties so that your users don't have to bother. For example, the following: @Value("${useDefault:ThisValue}") private String defaultValue; ...will inject ThisValue into defaultValue if a property called useDefault cannot be found. Taking this one step further, then specifying: @Value("${emptyDefault:}") private String emptyValue; ...will inject an empty string into emptyValue. If there’s a Spring suggestion box for minor, trivial improvements, then I’d like to suggest that you should be able to make properties optional, perhaps using something like this... @Value("${optional}" required=false) private String optionalPropertyValue; ...as a convenience feature that might save someone some heart-ache and time in the future. From http://www.captaindebug.com/2012/01/autowiring-using-value-and-optional.html

First of all you may be wondering, why do I want my own local Nuget Gallery? Well, here are two reasons: Having your own NuGet server is perfect for when you need share modules with other people on your team but you do not necessarily want to make them available for public consumption. If you are a consultant then having your own personal NuGet Gallery may be a handy way to keep your libraries and utilities accessible to you when you are on the road. This is an great way to utilize your home broadband connection. Last year I wrote an article about how to Build a NuGet Server with gold plating. At the time, there were two methods for hosting your own NuGet feed. The first option was to install the Orchard-based NuGet Gallery. I personally stayed away from this option because setting up an entire CMS just to host a few small NuGet packages seemed like overkill to me. The second option was to create an empty ASP.NET MVC site and install a few NuGet packages from Phil Haack that turned your empty website into a NuGet server. I call the second option the recursive NuGet server because you install NuGet packages which in turn help you to create a NuGet server. Anyway, if you compare the features of the Orchard Nuget Gallery to the recursive NuGet server, you will instantly notice that the Orchard version had a lot more functionality. Unfortunately, at the time I still could not justify setting up an entire CMS just to get a few small features. Eventually someone on the NuGet team realized that having the gallery so tightly coupled with Orchard was probably not a good idea. So sometime late last year, the NuGet gallery was removed from Orchard which made the setup process a lot less complex. Unfortunately the documentation page for Setting Up a Local NuGet Gallery has not been updated yet and still reflects the steps for creating the Orchard-based gallery. Since I recently setup a NuGet server at the office I decided to document the new steps in order to save you some trouble. Download the latest source from GitHub. I just grabbed the zip file since I do not have a Git client on my machine. Extract the zip file and navigate to the Website subdirectory. Locate the web.config file and open it up in your favorite editor. Inside the web.config you will want to change the following options: Modify the configuration/connectionStrings/NuGetGallery key so it points to your locally hosted SQL Server. Change the appSettings/GalleryOwnerEmail to the email address of the person who is going to administer the site. Change the appSettings/Configuration:SiteRoot to reflect the domain name you are going to use for the site. Run the Build-Solution.ps1 script using Powershell in the root directory. This will compile the website and assemble the binaries. Open up your IIS Manager Create a new application pool. The pool should use the 4.0 framework and use an integrated pipeline. Please pay careful attention to the Identity of the pool because you will need to grant this account permissions to your SQL Server. Create a new website. Set the site’s physical path to point at the Website directory. Also make sure the site uses the application pool that you created in the previous step. Do not start the website yet. Open up SQL Server Management Studio Grant db_creator to the identity of the application pool you created earlier. The account needs db_creator because the first time you run the applicaton, the Entity Framework context initializer will run. If no database exists yet then it will create the database for you. After, the database is created you can trim back the permissions to db_datareader and db_datawriter. This tends to make your DBA happy. Start your website and launch the browser of your choice. In the browser, navigate to the NuGet server. It may take a second or two for the page to appear because the database needs to get created during the first run. If you followed the steps properly then you should see the following page:

we are entering into the final part of this series, on large scale refactorings : this kind of operations is less predictable and less immediate. however, it is important to be able to perform them with small steps whenever necessary, if we don't want to get stuck in a situation with dozens of broken classes and no clear further step to take. sometimes larger investments are needed to avoid a tangled design: these large scale refactorings use the smaller refactorings as building blocks, but they work at an higher level of abstraction and affect many places in your codebase. why eliminating some inheritance levels? inheritance is easy to abuse , we got it by now. the main problem is its powerful ability to automatically copy and paste code, which leads to use *extends* any time there is duplication instead of any time there is an inexpressed is-a relationship between concepts.. the result is often that you have to jump up and down a hierarchy to follow the thread of execution, disrupting any separation of concerns between subclass and superclass. /the case we want to address today is the combinatorial explosions of concerns where each level of subclassing adds a dimension to the responsibility of the class. consider for example post and link as subclasses of newsfeeditem. at the second level, we may add facebookpost and twitterpost classes, inheriting from post. but also twitterlink and, maybe tomorrow, facebooklink. if we support linkedin, let's think about linkedinpost... the number of classes grow with the square of the elements involved. there are several solutions (like the decorator pattern), but our goal is always the same: keeping a hierarchy as small as possible by allowing a single categorization. when classes of a unique hierarchy can be put in a matrix, they grow with an order of magnitude more than when a single level of inheritance is present. fowler explains how a 3d or 4d matrix is even worse, and require this refactoring to be applied more times to each pair of dimensions. if you have ever seen a pair of withimagefacebookpost and textualfacebookpost classes... steps first, identify the different concerns to separate: all the dimensions you can put the classes on. in our continuing example, we are talking about the socialnetwork categorization and the item one. choose one of the two dimensions to keep in the current hierarchy, while the other will be extracted. perform extract class on the base class of the hierarchy, to introduce a collaborator. this will be the base class of the other hierarchy. introduce subclasses for the extracted object , for each of the original ones that have to be eliminated (so we're talking about only the second categorization.). initialize the current objects with them. move methods onto to the new hierarchy. you may have to extract them first. when subclasses contain only initialization, move the logic in the creation code and eliminate them. this refactoring is a great enabler for further moves: you can extract other collaborators or methods thanks to the reduced complexity of the hierarchies, that can now diverge. you can also simplify testing, by testing at the unit level and for single concerns. example i'll try to keep the logic as small as possible since these examples will use many classes already. in the initial situation, there is a hierarchy with two levels: newsfeeditem defines two abstract methods, the content() and the authorlink(), to use for displaying itself. post and link implements content(), while their subclasses implements authorlink() targeting facebook or twitter respectively. assertequals("enjoy!" . " -- php-cola", $post->__tostring()); } public function testafacebooklinkisdisplayedwithtargetandlinktotheauthor() { $link = new facebooklink("our new ad", "http://youtube.com/...", "php-cola"); $this->assertequals("our new ad" . " -- php-cola", $link->__tostring()); } public function testatwitterlinkisdisplayedwithtargetandlinktotheauthor() { $link = new twitterlink("our new ad", "http://youtube.com/...", "giorgiosironi"); $this->assertequals("our new ad" . " -- @giorgiosironi", $link->__tostring()); } } abstract class newsfeeditem { protected $author; public function __tostring() { return "" . $this->content() . " -- " . $this->authorlink() . ""; } /** * @return string */ protected abstract function content(); /** * @return string */ protected abstract function authorlink(); } abstract class post extends newsfeeditem { private $content; public function __construct($content, $author) { $this->content = $content; $this->author = $author; } protected function content() { return $this->content; } } abstract class link extends newsfeeditem { private $url; private $linktext; public function __construct($linktext, $url, $author) { $this->linktext = $linktext; $this->url = $url; $this->author = $author; } protected function content() { return "url\">$this->linktext"; } } class facebookpost extends post { protected function authorlink() { return "author\">$this->author"; } } class twitterlink extends link { protected function authorlink() { return "author\">@$this->author"; } } class facebooklink extends link { protected function authorlink() { return "author\">$this->author"; } } as you can see, the second level introduces some duplicated code that a composition solution will immediately fix. we choose to maintain post and link in the curent hierarchy, since they are also tied to $this->author. the new hierarchy will contain a facebook and a twitter related class. we add the source new base class for the second hierarchy, and a field in newsfeeditem to hold an instance of it: abstract class newsfeeditem { protected $author; protected $source; public function __tostring() { return "" . $this->content() . " -- " . $this->authorlink() . ""; } /** * @return string */ protected abstract function content(); /** * @return string */ protected abstract function authorlink(); } abstract class source { public function __construct($author) { $this->author = $author; } public abstract function authorlink(); } we add the two facebooksource and twittersource subclasses, and we initialize the $source field to the right instance via a init() hook method. a constructor would be equivalent, but right now we would have to delegate to parent::__construct() and that would be noisy. class facebooksource extends source { public function authorlink() { } } class twittersource extends source { public function authorlink() { } } class facebookpost extends post { public function init() { $this->source = new facebooksource($this->author); } protected function authorlink() { return "author\">$this->author"; } } class twitterlink extends link { public function init() { $this->source = new twittersource($this->author); } protected function authorlink() { return "author\">@$this->author"; } } class facebooklink extends link { public function init() { $this->source = new facebooksource($this->author); } protected function authorlink() { return "author\">$this->author"; } } we perform move method two times to move the authorlink() behavior in the collaborator. this means we have to delegate to $this->source in the base class newsfeeditem. abstract class source { public function __construct($author) { $this->author = $author; } public abstract function authorlink(); } class facebooksource extends source { public function authorlink() { return "author\">$this->author"; } } class twittersource extends source { public function authorlink() { return "author\">@$this->author"; } } now he second level subclasses only contain creation code: we can move eliminate them if we move this initialization in the construction phase, which is represented by the tests here. we can substitute $this->author with $this->source: assertequals("enjoy!" . " -- php-cola", $post->__tostring()); } public function testafacebooklinkisdisplayedwithtargetandlinktotheauthor() { $link = new facebooklink("our new ad", "http://youtube.com/...", new facebooksource("php-cola")); $this->assertequals("our new ad" . " -- php-cola", $link->__tostring()); } public function testatwitterlinkisdisplayedwithtargetandlinktotheauthor() { $link = new twitterlink("our new ad", "http://youtube.com/...", new twittersource("giorgiosironi")); $this->assertequals("our new ad" . " -- @giorgiosironi", $link->__tostring()); } } abstract class newsfeeditem { protected $author; protected $source; public function __tostring() { return "" . $this->content() . " -- " . $this->source->authorlink() . ""; } /** * @return string */ protected abstract function content(); } we can now instantiate directly post and link by making them concrete instead of abstract. you may want to bundle this step with the previous one as it intervene on the same code. a consequence is that we can throw away the second level subclasses. class teaseapartinheritance extends phpunit_framework_testcase { public function testafacebookpostisdisplayedwithtextandlinktotheauthor() { $post = new post("enjoy!", new facebooksource("php-cola")); $this->assertequals("enjoy!" . " -- php-cola", $post->__tostring()); } public function testafacebooklinkisdisplayedwithtargetandlinktotheauthor() { $link = new link("our new ad", "http://youtube.com/...", new facebooksource("php-cola")); $this->assertequals("our new ad" . " -- php-cola", $link->__tostring()); } public function testatwitterlinkisdisplayedwithtargetandlinktotheauthor() { $link = new link("our new ad", "http://youtube.com/...", new twittersource("giorgiosironi")); $this->assertequals("our new ad" . " -- @giorgiosironi", $link->__tostring()); } } the final result can be thought of as a bridge pattern, or just good factoring: a further step could be to divide these tests into unit ones, only exercising a newsfeeditem or a source object. but that's a story for another day...

Right now, when I try to persist an object in Google App Engine, I’m facing the error “Java.lang.VerifyError: Expecting a stackmap frame at branch target“. I’m using JDK 7 and it seems like the problem lies with this JDK. After googling a bit, I found that there seems to be two solutions to fix this problem. Solution 1: Change to JDK 6 As simple as is, change your JDK to version 6 and you won’t be bugged by this exception anymore. Well, in my case, I have to use JDK 7. So, moving on to the solution 2. Solution 2: Configure JVM Go to Windows -> Preferences -> Installed JREs. Select the default JVM and click edit. Then add this parameter as VM argument “-XX:-UseSplitVerifier” as seen below. This should solve the issue. From http://veerasundar.com/blog/2012/01/java-lang-verifyerror-expecting-a-stackmap-frame-at-branch-target-jdk-7/

One of the handy things about using Maven is that, by default, the names of the artifacts it creates include the current version number from the POM's version tag. It doesn’t matter what type of artifact it is, whether it’s a JAR, WAR or EAR you generally end up with something like this: my_module-1.2.3-RELEASE.jar And this is all usually fine when you’re dealing with a project that’s built solely using Maven. It does, however, become a little more inconvenient if you’re developing JAR files with Maven, but your WAR file is developed using Ant. In this case, when you have to check files in to the /WEB-INF/libs directory yourself (perish the thought) and your JAR file changes often, you end up constantly adding and deleting files from your version control system. From experience, it turns out to be more convenient, in terms of file management, if you remove the version number from the JAR file name and use something like this: my_module.jar However, there will always be the need to know the version of your JAR that has been included in your webapp’s WAR file and that’s where the maven-jar-plugin comes in handy. This allows you to write custom information into your JAR file’s manifest as shown by the POM file snippet below. ${project.artifactId} org.apache.maven.plugins maven-jar-plugin 2.3.2 true ${project.name} development ${project.groupId} ${project.artifactId} ${project.version} The POM file extract above contains two handy features. The first: ${project.artifactId} ...removes the version number from the JAR file name by specifying the finalname tag. In this case the finalname has been set to the project.artifactId. This means that if your artifact tag looks something like this... my_module ...then your jar file will be called: my_module.jar For more on Maven’s default properties take a look at this blog from last January. The second task accomplished by the POM extract above is to use the maven-jar-plugin to add group, artifact and version information to the jar’s manifest file. The lines that are responsible for this are: ${project.groupId} ${project.artifactId} ${project.version} You can obviously add any information you want to a jar’s manifest file, but in this scenario, adding the version number was extremely useful when it came to support and tracing problems. From http://www.captaindebug.com/2012/01/adding-version-information-to-your-jars.html

A short definition of an Android Parcel would be that of a message container for lightweight, high-performance Inter-process communication (IPC). On Android, a "process" is a standard Linux one, and one process cannot normally access the memory of another process, so with Parcels, the Android system decomposes objects into primitives that can be marshaled/unmarshaled across process boundaries. But Parcels can also be used within the same process, to pass data across different components of a same application. As an example, a typical Android application has several screens, called "Activities" , and needs to communicate data or action from one Activity to the next. To write an object than can be passed through, we can implement the Parcelable interface. Android itself provides a built-in Parcelable object called an Intent which is used to pass information from one component to another. Using an Intent is pretty straightforward. Let's say we're collecting user data from our initial screen called CollectDataActivity. // inside CollectDataActivity, construct intent to pass along the next Activity, i.e. screen Intent in = new Intent(this, ProcessDataActivity.class); in.putExtra("userid", id); // (key,value) pairs in.putExtra("age", age); in.putExtra("phone", phone); in.putExtra("is_registered", true); // call next Activity --> next screen comes up startActivity(in); We need to collect that information from our data collection screen to process it. So all we do is the following: // inside ProcessDataActivity, get the info needed from previous Activity Intent in = this.getIntent(); in.getLongExtra("userid", 0L); in.getIntExtra("age", 0); in.getStringExtra("phone"); in.getBooleanExtra("is_registered", false); // false = default value overridden by user input Again, pretty straightforward. We retrieve the data using the same keys used to send it, and using our Intent's corresponding methods for each data type. But even when communicating with Intents, we can still use Parcels to pass data within the intent. For instance, we can do the above in a more elegant way using a custom, Parcelable User class: In the first Activity: // in CollectDataActivity, populate the Parcelable User object using its setter methods User usr = new User(); usr.setId(id); // collected from user input// etc.. // pass it to another component Intent in = new Intent(this, ProcessDataActivity.class); in.putExtra("user", usr); startActivity(in); In the second Activity: // in ProcessDataActivity retrieve User Intent intent = getIntent(); User usr = (User) intent.getParcelableExtra("user"); And this is what a Parcelable User class looks like: import android.os.Parcel; import android.os.Parcelable; public class User implements Parcelable { private long id; private int age; private String phone; private boolean registered; // No-arg Ctor public User(){} // all getters and setters go here //... /** Used to give additional hints on how to process the received parcel.*/ @Override public int describeContents() { // ignore for now return 0; } @Override public void writeToParcel(Parcel pc, int flags) { pc.writeLong(id); pc.writeInt(age); pc.writeString(phone); pc.writeInt( registered ? 1 :0 ); } /** Static field used to regenerate object, individually or as arrays */ public static final Parcelable.Creator CREATOR = new Parcelable.Creator() { public User createFromParcel(Parcel pc) { return new User(pc); } public User[] newArray(int size) { return new User[size]; } }; /**Ctor from Parcel, reads back fields IN THE ORDER they were written */ public User(Parcel pc){ id = pc.readLong(); age = pc.readInt(); phone = pc.readString(); registered = ( pc.readInt() == 1 ); } } What we did was: Make our User class implement the Parcelable interface. Parcelable is not a marker interface, hence what follows: Implement its describeContents method, which in this case does nothing. Implement its abstract method writeToParcel, which takes the current state of the object and writes it to a Parcel Add a static field called CREATOR to our class, which is an object implementing the Parcelable.Creator interface Add a Constructor that takes a Parcel as parameter. The CREATOR calls that constructor to rebuild our object. This looks like a lot of extra code at first, but bear in mind that, as in most cases, our application might evolve into incorporating more data from the user... Sometimes we need to pass complex objects from one component to another, and passing an object yields a cleaner design. The same logic applies for communicating between an Activity (foreground UI) and a background Service. We would just call the startService method instead of startActivity and pass it our Parcelable User object. Note that a Service is not running in a separate process by default. At this point, there are a couple of questions that may be raised: Isn't using an IPC-friendly, custom object for in-process communication simply overkill? Why would we want to use Parcelable, when we already have built-in Java serialization? The answer to the first concern is...maybe. But communicating through a custom object than through a list of key-value pairs is more OO, and it has no noticeable negative performance impact. As for the second question, why not simply have User implement Serializable, a theoretically simpler, marker interface? In one word, performance. Using Parcels is more efficient than serializing, at the price of some added complexity. That extra efficiency has in turn its limits: passing an image ( Bitmap) using Parcelable is generally not a good idea (although Bitmap does in fact implement Parcelable). A much more memory-efficient way would be to pass only its URI or Resource ID, so that other Android components in your application can have access to it. Another limitation of Parcelable is that it must not be used for general-purpose serialization to storage, since the underlying implementation may vary with different versions of the Android OS. So yes, Parcels are faster by design, but as high-performance transport, not as a replacement for general-purpose serialization mechanism. Having said all that, since our User object is Parcelable, it can now be sent from this application to another one running in another process, in particular through an interface implementing a remote service. In an upcoming post, we'll look at IPC and Android's Interface Definition Language (AIDL). from Tony's Blog

i want to share something a software developer or operations guy every now and then encounters. and which i did yesterday. it all started with our nightly maven build failing last saturday jan 28 on a java.lang.noclassdeffounderror: javax/xml/bind/validationeventlocator the interesting snippet from the concole output from this build looked like this: [info] [jaxb2:generate {execution: xxx-schema-gen}] [fatal error] org.jvnet.mjiip.v_2.xjc2mojo#execute() caused a linkage error (java.lang.noclassdeffounderror) and may be out-of-date. check the realms: [fatal error] plugin realm = app0.child-container[org.jvnet.jaxb2.maven2:maven-jaxb2-plugin] urls[0] = file:/home/hudson/.m2/repository/org/jvnet/jaxb2/maven2/maven-jaxb2-plugin/0.8.1/maven-jaxb2-plugin-0.8.1.jar urls[1] = file:/home/hudson/.m2/repository/org/jvnet/jaxb2/maven2/maven-jaxb2-plugin-core/0.8.1/maven-jaxb2-plugin-core-0.8.1.jar urls[2] = file:/home/hudson/.m2/repository/com/sun/org/apache/xml/internal/resolver/20050927/resolver-20050927.jar urls[3] = file:/home/hudson/.m2/repository/org/sonatype/plexus/plexus-build-api/0.0.7/plexus-build-api-0.0.7.jar urls[4] = file:/home/hudson/.m2/repository/org/codehaus/plexus/plexus-utils/1.5.15/plexus-utils-1.5.15.jar urls[5] = file:/home/hudson/.m2/repository/org/jfrog/maven/annomojo/maven-plugin-anno/1.3.1/maven-plugin-anno-1.3.1.jar urls[6] = file:/home/hudson/.m2/repository/org/jvnet/jaxb2/maven2/maven-jaxb22-plugin/0.8.1/maven-jaxb22-plugin-0.8.1.jar urls[7] = file:/home/hudson/.m2/repository/com/sun/xml/bind/jaxb-impl/2.2.5-b10/jaxb-impl-2.2.5-b10.jar urls[8] = file:/home/hudson/.m2/repository/com/sun/xml/bind/jaxb-xjc/2.2.5-b10/jaxb-xjc-2.2.5-b10.jar [fatal error] container realm = plexus.core.maven [info] ------------------------------------------------------------------------ [error] fatal error [info] ------------------------------------------------------------------------ [info] javax/xml/bind/validationeventlocator [info] ------------------------------------------------------------------------ [info] trace java.lang.noclassdeffounderror: javax/xml/bind/validationeventlocator at com.sun.tools.xjc.reader.internalizer.domforestscanner.scan(domforestscanner.java:84) it seems that the maven-jaxb2-plugin –we use for jaxb to generate java sources for a certain schema–suddenly triggers a (missing or incompatible?) dependency. the weird thing is the “suddenly” part, since the last commit was done on friday after which the normal continuous builds ran fine and the even the nightly build on midnight friday to saturday. we use maven to take care of these things right? always have a known set of dependencies, each part of the process? ofcourse at the time things didn’t seem so obvious. first thing i wondered, could it have something do to with a java 5 vs 6 problem? as a matter of fact, on our project we’re trying to go to java 6 after a long time, but i’m the only one which already upgraded my local developer machine to work with jdk6 for a while and see if nothing strange happens. you know, keeping a lot of files from your workspace in a special “do not commit” working set or hidden from view, in order to prevent it from prematurely ending up in version control so naturally, i first explored all changesets leading up to the failed build to see if i by accident committed a file i shouldn’t have. but i couldn’t find anything. next i thought: could hudson be configured incorrectly last week by a parting co-worker (which had a somewhat unofficial ownership of our ci infrastructure until he left) which now surfaced, because e.g. a server was restarted or hudson was upgraded? checked a few things out: our hudson startup.sh looked like /usr/java/latest/bin/java -jar hudson.war --httpport=9090 --ajp13port=9091 --deamon --logfile=hudson.log & where /usr/java/latest/bin/java pointed to “java(tm) se runtime environment (build 1.6.0 _24-b07)” while normal “java” on the command-line pointed to “java(tm) 2 runtime environment, standard edition (build 1.5.0 _22-b03)” . could it be that the “latest” directory pointed earlier to java 5 en (by some mysterious upgrade on the server) now suddenly links to java 6. could the java version we start hudson with affect the java version we use for our hudson jobs? i don’t hope so! consequently, i checked the hudson configuration itself: what kind of jdk’s did we configure? luckily, only one: named “1_5_0″ with java_home pointing to “/usr/java/default”. but again not clear from the path to what java version it points, until i figured out this symlink leads to “/usr/java/jdk1.5.0_22″. good, jdk 5 should be used as default for all our maven builds. to verify i added a 2nd bogus jdk entry in the hudson configuration, so i was able to explicitly choose it in the job configuration – and after triggering a new build i was sure hudson was configured correctly jdk-wise. man, how one can digress! so let’s take a look at the offending library at hand. from the stacktrace one can spot the maven-jaxb2-plugin artefact from the group org.jvnet.jaxb2.maven2 . did something happen to this dependency itself? i opened up our nexus console, searched for it and saw the screen below: wait a minute! why do we have two versions of this plugin? in nexus i opened up the tab artefact information on the 0.8.1 version and saw that the uploaded date listed last saturday 28th of jan. i know we shouldn’t have more than one version of this plugin in nexus. did a small check on the jira release notes page of this plugin… well then. so a new release of the plugin was published online last saturday and the nightly build triggered the download of a new version 0.8.1 – which seemed to be compiled against java 6 now which caused the java.lang.noclassdeffounderror . this naturally lead me to the offending part in our pom.xml : org.jvnet.jaxb2.maven2 maven-jaxb2-plugin argh. no version! changed it into: org.jvnet.jaxb2.maven2 maven-jaxb2-plugin 0.8.0 i committed the pom.xml and triggerd a manual build – and… it worked. ofcourse. in conclusion there are some lessons to be learned i think: when debugging a problem, always try to reason about possible paths which come to mind to follow first and don’t get hung on your very first idea which pops up. this got me i think sidetracked too long on finding out whether or not i accidentally committed java 6 files or whether or not hudson got accidentally misconfigured into not using java 5 anymore somehow. troubleshooting skills are highly dependent of previous experience in a field and ofcourse, if ever a similar problem arises i’d be able to recognize it faster now. write it down – so a collegue or yourself can find it back more easily later on. explicity set dependency versions in your pom.xml! don’t blame maven for everything does anyone else have a troubleshooting-tale of going in the wrong direction? original posting: http://tedvinke.wordpress.com/2012/02/01/why-does-my-maven-build-fail

While Kotlin programming language prepares for the public early access program I want to share with you one an example how easly it can be used with existing Java codebases. This short note does not intend to teach the reader how to use Kotlin but only to make him/her intersted to learn. We will create small toy application using Kotlin and the charming Guice framework. The application is nothing more than the usual "Hello, World!" but it contains an application service and logging service and each service will have two incarnations - for testing and for production use. Let us start with an abstract LoggingService. It will be an abstract class with only one abstract method to output the passed string. Most probably the code below does not require much explaination. abstract class LoggingService() { abstract fun info(message: String?) } Now we will define a simple implementation, which prints the given message to the standard output class StdoutLoggingService() : LoggingService(){ override fun info(message: String?) = println("INFO: $message") } override modifier tells the compiler that the method overrides some method of a superclass. Note also string interpolation Now we will create a little more sophisticated implementation, which we will use in production :) class JdkLoggingService [Inject] (protected val jdkLogger: Logger) : LoggingService() { override fun info(message: String?) = jdkLogger.info(message) } [Inject] annotation on constructor tells Guice how to create JdkLoggerService. val on constructor parameter asks to create final property initialized by given value. var asks for non-final one and neither of them define simple constructor parameter Now we are ready to define the abstract application service and both implementations of it for test and production use. abstract class AppService(protected val logger: LoggingService, protected val mode: String) { fun run() { logger.info("Application started in '$mode' mode with ${logger.javaClass.getName()} logger") logger.info("Hello, World!") } } class RealAppService [Inject] (logger: LoggingService) : AppService(logger, "real") class TestAppService [Inject] (logger: LoggingService) : AppService(logger, "test") Note how elegantly Kotlin allows us to define properties and pass values to superconstructor Now we go to more interesting part - creating min-DSL for Guice. But let us start with how we want our application to look like. fun main(args: Array) { fun configureInjections(test: Boolean) = injector { +module { if(test) { bind().toInstance (StdoutLoggingService()) bind().to () } else { bind().to() bind().to () } } } configureInjections(test=false).getInstance ().run() } There are few things to notice here We use local function to configure injections. It is not necessary but allow some nice code grouping. Return type of function configureInjections is inferred from it's body (call to finction injector - root of our DSL which we will define soon) We call configureInjections using named arguments syntax. It is not necessary in our case but very convinient when we have many parameters and some of them are optional. Now it is time to define simple parts of our DSL. It will be three extension functions for some Guice classes. fun Binder.bind() = bind(javaClass()).sure() fun AnnotatedBindingBuilder.to() = to(javaClass()).sure() fun Injector.getInstance() = getInstance(javaClass()) Please read about extension functions in Kotlin documentation Note in variance used in function 'to'. Please read about generics and variance in Kotlin documentation. It is really interesting javaClass() call is Kotlin standard library for Java (remember that Kotlin can be compiled for other platforms like javascript as well) is equivalent to T.class in Java. The huge difference here is that in Kotlin it applicable not only to real classes but also to generic type parameters (thanks to runtime type information). Call to method sure() is Kotlin way (soon to be replaced by special language construct) to ensure non-nullability. As Java has not notation of nullable and non-nullable types we need to take some care on integration point. Please read amazing story of null-safety in Kotlin documentation. Finally we are ready to most complex part - definition of method injector. fun injector(config: ModuleCollector.() -> Any?) : Injector { val collector = ModuleCollector() collector.config() return Guice.createInjector(collector.collected).sure() } It has one parameter of type ModuleCollector.()->Any? which means "extension function for ModuleCollector(we will define ModuleCollector few lines below), which does not accept any parameters and returns value of any type potentially nullable" The implementation is very straight-forward we create ModuleCollector we use it as receiver to call given configuration function we ask Guice to create Injector for all modules configured (consult Guice documentation for details) This is extremely powerful method of defining DSLs in Kotlin As we saw above we call method injector with function block expression. The fact that parameter is extension function makes all (modulo visibility rules) methods of ModuleCollector available inside function block. The last part of our DSL is definition of ModuleCollector. It contains internal list of collected modules and only two methods method module - uses variation of the same extension-function-as-parameter trick - we use extension function to implement method of anonimous class. Please consult Kotlin documentation on object expressions method plus - overrides unary plus operation Please consult Kotlin documentation on operator overloading. It is very important to note that this method is both extension method and member of class ModuleCollector. It allows very good context catching on call site. In our case above we call this method inside extention function with ModuleCollectoror receiver and apply it to Module created by call to method Module. class ModuleCollector() { val collected = ArrayList () fun module (config: Binder.()->Any?) : Module = object: Module { override fun configure(binder: Binder?) { binder.sure().config() } } fun Module.plus() { collected.add(this) } } We are done. I hope that was interesting. This note is a very brief and non-detailed introduction on goodies of Kotlin. If this has motivated you to read more about Kotlin then my goal is achieved. Thank you and till next time!