Featured FREE Whitepapers

What's New Here?


Best Of The Week – 2012 – W03

Hello guys, Time for the “Best Of The Week” links for the week that just passed. Here are some links that drew Java Code Geeks attention: * Best development tools in the cloud: In this article, the best cloud-based development tools are presented. Source Control, Agile project management, Collaboration, Continuous Integration and Automated Testing tools are discussed. Also check out Developing and Testing in the Cloud and Services, practices & tools that should exist in any software development house. * JBoss Releases Hibernate 4.0: This article discusses the release of Hibernate 4.0 by JBoss. The new release includes features such as Multi-tenancy support, introduction of the “Services” API, better logging with i18n support, preparation for OSGi support and various code cleanups. * Writing Applications for Cloud Foundry Using Spring and MongoDB: A presentation on how to create Spring applications using Spring Data and MongoDB, applications deployed on Cloud Foundry. Also check out Using MongoDB with Morphia. * How I Program Stuff: An interesting approach on how to program that involves isolation from distraction, elimination of redundant stuff and ruthless coding. * Android Essentials: Create a Mirror: This tutorial demonstrates how to create a mirror app for your Android phone using the in built front facing camera. Also check out Android HTTP Camera Live Preview Tutorial. * Oracle and the Java Ecosystem: An overview of Oracle’s current position in the Java ecosystem. Discusses topics like the Java Community Process (JCP), OpenJDK with its newly renewed interest and how Android fits in all these. * Just-In-Time Logging: An interesting article that discusses logging and proposes moving it from the province of the developer’s discretion to the circle of architecture and design results in just-in-time logging. On the same topic, also read 10 Tips for Proper Application Logging. * How to get the most out of Spring and Google App Engine: This presentation will get you up and running building Spring apps on Google App Engine. Explains step-by-step how to build a real Spring app and identifies not only the basics of App Engine, but more advanced topics such as integrating with Google’s SQL Service and using App Engine’s “Always on” feature. Also check out Spring MVC and REST at Google App Engine. * How Many Hours Can a Programmer Program?: This article discusses programmer’s productivity and how working more hours than usually can affect one’s life. * Creating Your First Spring Web MVC Application: Detailed tutorial to get you started with a Spring Web MVC application. Also check out Spring MVC Development – Quick Tutorial and Spring MVC3 Hibernate CRUD Sample Application. * How Do You Pick Open Source Libraries?: A nice article with pointers on how to pick open source libraries like how well does it fit to a specific scenario, how popular it is, what the code quality is, the location of code and issue tracker and the underlying license. * Java verbosity, JEE and Lombok: This post discusses how to minimize some of Java’s verbosity by using the Lombok project. More specifically, apart from the Java beans related code, the benefits of Lombok with JPA Entities and JAXB Content Objects are discussed. * Is it time to get rid of the Linux OS model in the cloud?: A nice article with pointers on how to pick open source libraries like how well does it fit to a specific scenario, how popular it is, what the code quality is, the location of code and issue tracker and the underlying license. * JVM Performance Tuning (notes): An article with some quick and dirty JVM performance tuning tips focusing on memory management, object allocation and garbage collection. Also check out Profile your applications with Java VisualVM and Practical Garbage Collection, part 1 – Introduction. * The Principles of Web API Usage: This article describes the basic principles of using a web API, such as reading the provided documentation, using the appropriate version, checking the change log, taking usage limits under consideration, caching data, using the appropriate data format, handling authentication etc. That’s all for this week. Stay tuned for more, here at Java Code Geeks. Cheers, Ilias Tsagklis Related Articles:Best Of The Week – 2012 – W02 Best Of The Week – 2012 – W01 Best Of The Week – 2011 – W53 Best Of The Week – 2011 – W52 Best Of The Week – 2011 – W51 Best Of The Week – 2011 – W50 Best Of The Week – 2011 – W49 Best Of The Week – 2011 – W48 Best Of The Week – 2011 – W47 Best Of The Week – 2011 – W46...

GWT – Pros and Cons

I love JavaScript. With the advent of jQuery and Mootools, my love for JavaScript has only increased plenty-fold. Given a choice I would use either of the aforementioned frameworks for any web application I develop. But being in the service industry, time and again I have to succumb to the client’s pressure and work in their choice of technology – whether or not it is the right one (The one who pays the piper calls the tune. Isn’t it?). One such client exposed me to the world of GWT. I have given GWT a shot couple of years back on the day it was released. I didn’t like it that much then, so I dismissed it and never returned back. But, over the past six months working on this project I have a slightly different impression on this framework. I still cannot say that GWT is the next big thing since sliced bread, but at least it is not as bad as I thought it was. I have just documented my observations, both good and bad during the course of this project and thought some fellow developer might find it useful while evaluating GWT. Pros:If you are a Java veteran with experience in Swing or AWT, then choosing GWT should be a no-brainer. The learning curve is the least with this background. Even if you are not experienced in Java GUI development, the experience in working on server-side Java for years will come in handy while developing GWT apps You can create highly responsive web applications with heavy lifting on the client-side and reduced chattiness with the server-side Although there are numerous JavaScript libraries out in the wild and most of them are worth their salt, many conventional developers don’t understand its true power. Remember, a powerful language like JavaScript is a double-edged sword. If you don’t know how to use it, even you won’t be able to clean the mess you create You can migrate from a typical web application to a GWT application iteratively. It is not an all or nothing proposition. You can use a clever trick called JSNI to interact with loads of JavaScript functions you already possess. But it is always better to move them to GWT sooner rather than later The IDE support for GWT cannot be better. Java IDEs have matured over the past decade to be one of the best in the world and GWT can take direct advantage of it The integrated debugging beauty is something you can kill for. The excellent debugging support offered by the mature Java IDEs is one feature that could sway anybody’s decision in favor of GWT The built-in IDE support to refactor Java code can directly be put to good use to maintain a simple design at all times. Doing this in JavaScript is not for the faint at heart The IDE syntax highlighting, error checking, code completion shortcuts etc are overwhelming – to say the least GWT is being actively developed by Google. We know that the project is not going to die off anytime soon. Until now their commitment towards the project says a lot about its future in the industry. The community behind the project is also a big PLUS. Discussions take place daily in Stack overflow, discussion forums, wikis and personal blogs. A simple search with the right keyword could point you in the right direction GWT is a well thought-out API; not something that was put together in a hurry. This helps you as a developer to quickly comprehend the abstractions and makes it really intuitive to use You can use GWT’s built-in protocol to transfer data between the client and the server without any additional knowledge of how the data is packaged and sent. If you prefer more control, you can always use XML, JSON or another proprietary format of your choice. Even in that case, while using JSON, you don’t have to use an non-intuitive java JSON library. You can use JSNI to ‘eval’ the JSON using straight javascript. Cool huh! You have the advantage of being able to use standard Java static code analyzers like FindBugs, CheckStyle, Detangler, PMD etc to monitor code and design quality. This is very important when you are working in a big team with varying experience. You can use JUnit or Test NG for unit testing and JMock or another mock library for mocking dependencies. Following TDD is straight-forward if you already practice it. Although there are JavaScript based unit testing frameworks like jsunit and qunit, come on tell me how many people already know that or are itching to use that. The GWT compiler generates cross-browser JavaScript code. Today, any marketing person who says this will probably be beaten. It has now become a basic necessity, not a luxury The GWT compiler optimizes the generated code, removes dead code and even obfuscates the JavaScript for you all in one shot Although the compilation process takes hell a lot of time, you don’t have to go through that during development. There is a special hosted mode that uses a browser plug-in and direct java byte-code to produce output. That is one of the main reasons you are able to use a Java debugger to debug client side code. Rich third-party controls are available through quite a few projects like Smart GWT, Ext GWT etc. They are well designed, easy to use and theme-able. So, if you have a requirement where existing controls don’t just cut it, you should be looking into one of these projects. There is a really fat chance that one of those components will work out. Even if that doesn’t work out, you can always roll out your own. GWT emphasizes the concept of a stateful client and a stateless server. This results in extremely less load on the server where many users have to co-exist and high load on the client where only one user is working I18N and L10N are pretty straight-forward with GWT. In fact locale based compilation is taken care by the GWT compiler itself. The same cannot be said about regular client-only frameworks GWT comes built-in with browser back button support even while using AJAX. If you are an AJAX developer, I can almost feel your relief. This is priceless.Cons:GWT is a fast developing project. So, there are a lot of versions floating around. Many functions, interfaces and events get deprecated and keeping up with their pace is not too much fun when you have other work to do There were quite a few GWT books during the beginning. Not so much these days. For example, I haven’t found many books on the 2.0 version of GWT. This leaves us only with Google’s documentation. I agree that the documentation is good and all, but nothing can beat a well written book GWT is not fun to work with. After all it is Java and Java is not a fun language to work with. If you add the fact that entire layouts and custom controls should be created in java, you can easily make a grown programmer cry. With the introduction of UI binder starting version 2.0, that problem is kind of solved, but now you have a new syntax to learn. The Java to JavaScript compilation is fairly slow, which is a significant con if you choose GWT. I personally prefer defining structure in HTML and styling it using CSS. The concepts used in HTML are clean and straight-forward and I have years of experience doing just that. But in GWT, I am kind of forced to use proprietary methods to do the same. That combined with the fact that GWT doesn’t solve the styling and alignment incompatibilies for me compounds the problem. So, writing layout code in GWT is something I despice. But with UI Binder and HTMLLayout from version 2.0 onwards, I feel I am back in my own territory It requires some serious commitment levels to get into GWT, coz, after that, a change in client side technology could require a complete rewrite of your app, as it is a radically different approach than other client side frameworks There is not a defined way to approach an application development using GWT. Should we use only module per app or one module per page or somewhere in between. These design patterns are slowly evolving only now. So, typically people tend to develop all in one module until the module size goes beyond being acceptable and then they refactor it into multiple modules. But if it is too late, then refactoring could not be that easy either Mixing presentation and code doesn’t sound right although typical desktop GUI applications does just that. But these days, even desktop application frameworks like Flex and Silverlight have taken an XML based declarative approach to separate presentation from logic. I think GWT 1.x version had this disadvantage. With the introduction of UI Binder starting from version 2.0, I think this disadvantage can be written off although it is yet another painful XML language to learn You would often be punching in 3X to 5X more code than you would with other client libraries – like jQuery – to get simple things done You should also remember that with GWT, the abstraction away from HTML isn’t complete. You’ll still need to understand the DOM structure your app is generating in order to style it, and GWT can make it harder to see this structure in the code. GWT is an advantage only for Java developers. Developers with .NET or PHP background won’t gain anything here If you have tasted the power of JavaScript and know how to properly utilize it to your advantage, then you will feel crippled with an unexpressive language like JavaI am sure many of you will have differences of opinion. Difference is good. So, if you think otherwise, feel free to leave a comment. We’ll discuss… References:  GWT – Pros and Cons from our JCG partner Ganeshji Marwaha at the Ganesh blog....

Domain-Driven Design Using Naked Objects

I just had a chance to read a newly released book, ‘Domain-Driven Design Using Naked Objects’ by Dan Haywood [http://www.pragprog.com/titles/dhnako] that provides an insight into the world of DDD. If nothing else, this book is for techies & management people alike. Although Naked Objects is covered as the implementation framework (to explain practically, all aspects of DDD), this book serves as an excellent introduction text for all of us who are new into this concept of crafting an enterprise application according to domain. This book also deserves to be read specially because there has been considerable buzz around this ‘Domain’ stuff in the recent past. According to the book , ‘Domain-driven design is an approach to building application software that focuses on the bit that matters in enterprise applications: the core business domain. Rather than putting all your effort into technical concerns, you work to identify the key concepts that you want the application to handle, you try to figure out how they relate, and you experiment with allocating responsibilities (functionality). Those concepts might be easy to see (Customers, Products, Orders, and so on), but often there are more subtle ones (Payable, ShippingRecipient, and RepeatingOrder) that won’t get spotted the first time around. So, you can use a team that consists of business domain experts and developers, and you work to make sure that each understands the other by using the common ground of the domain itself.’ Since being a domain expert is the next step for any developer naturally, as his experience increases, there is need to have more insight into the business stuff, instead of just the software. UML although does a great job for explaining the Object Oriented stuff, but ponder for a second, how is it really going to help a businessman that is interested in getting more profits. Naked Objects framework (http://www.nakedobjects.org) is based on the design pattern with same name(http://en.wikipedia.org/wiki/naked_objects) is an open source framework (only for java, .NET is a commercial one) that converts simple bean/components automatically into an interface(read as  multiple applications). Don’t yet confuse this with prototyping because DDD incorporates both the developer and the domain expert teams and we are not just creating the UI. DDD’s 2 central premises explained :A ubiquitous language for integrating & easing communication between domain experts instead of 2, which is the existing norm(like code & UML) Using model-driven design that aims to capture the model of the business process. This is done in code, rather than just visually, as was the case earlier.Naked Objects The java based Naked Objects(NO) framework is an evolutionary step forward from Rails (and its other avatars : Grails, Spring Roo, asp.net MVC, etc) that focuses more on M & V rather than MVC and provides much more domain-specific applications in turn resulting in flexibility for all. A typical NO application consists of multiple sub-projects like the core domain, fixture, service, command line and webapp project through a maven archetype. The coolest thing  is that NO automatically displays the domain objects in an O-O based UI that offers display in more flexible manner than any other IDE. NO also challenges the common frontend-middleware-backend convention and instead applies the Hexagonal architecture (http://alistair.cockburn.us/Hexagonal+architecture) that deals with the bigger picture in mind. The development in this framework is pojo centric and is heavily based on annotations, which should be pretty much regular stuff for any JEE developer. Also, during my initial evaluation of the framework, the code that’s being generated during the development is of maintainable quality, which is virtually essential for maintenance and scaling in any enterprise application. Hence this book, and its field of study is highly recommended for any enterprise developer/ team/ manager/ domain expert and as is repeatedly mentioned, becomes highly important when one has more years of experience under his belt. I am continuing my exploration in this and if it is really useful for me, would post some exercises here. Reference: Domain-Driven Design Using Naked Objects from our JCG partner Sumit Bisht at the Sumit Bisht blog....

WhateverOrigin – Combat the Same Origin Policy with Heroku and Play! Framework

A little while ago, while coding Bitcoin Pie, I found the need to overcome the notorious Same Origin Policy that limits the domains javascript running on a client’s browser can access. Via Stack Overflow I found a site called Any Origin, that’s basically the easiest way to defeat Same Origin Policy without setting up a dedicated server. All was well, until about a week ago, Any Origin stopped working for some (but not all) https requests. It just so happened that in that time I had gained some experience with Play! and Heroku, which enabled me to quickly build an open source clone of Any Origin called Whatever Origin (.org!) (on github). For those unfamiliar with Play! and Heroku, let me give a short introduction: Heroku is one of the leading PaaS providers. PaaS is just a fancy way of saying “Let us manage your servers, scalability, and security … you just focus on writing the appliaction.” Heroku started as a Ruby shop, but they now support a variety of programming languages and platforms including python, java, scala, javascript/Node.Js. What’s extra cool about them is that they offer a huge set of addons ranging from simple stuff like Custom Domains and Logging through scheduling, email, SMS, and up to more powerful addons like Redis, Neo4j and Memcached. Now for the application part, I had recently found Play! Framework. Play is a Java/Scala framework for writing web applications that borrows from the Ruby on Rails / Django ideas of providing you with a complete pre-built solution, letting you focus on writing your actual business logic, while allowing you to customize everything later if needed. I encourage you to watch the 12 minute video on Play!’s homepage, it shows how to achieve powerful capabilities from literally scratch. Play! is natively supported at Heroku, so really all you need to do to get a production app running is:play new Write some business logic (Controllers/Views/whatnot) git init … git commit “heroku apps add” to create a new app (don’t forget to add “–stack cedar” to use the latest generation Cedar stack) “git push heroku master” to upload a new version of your app … it’s automatically built and deployed.Armed with these tools (which really took me only a few days to learn), I set out to build Whatever Origin. Handling JSONP requests is an IO-bound task – your server basically does an HTTP request, and when it completes, it sends the response to your client wrapped in some javascript/JSON magic. Luckily Play!’s support for Async IO is really sweet and simple. Just look at my single get method: public static void get(final String url, final String callback) { F.Promise<WS.HttpResponse> remoteCall = WS.url(url).getAsync(); await(remoteCall, new F.Action<WS.HttpResponse>() { public void invoke(WS.HttpResponse result) { String responseStr = getResponseStr(result, url); // code for getResponseStr() not included in this snippet to hide some ugly irrelevant details // http://blog.altosresearch.com/supporting-the-jsonp-callback-protocol-with-jquery-and-java/ if ( callback != null ) { response.contentType = "application/x-javascript"; responseStr = callback + "(" + responseStr + ")"; } else { response.contentType = "application/json"; } renderJSON(responseStr); } }); }The first line initiates an async fetch of the requested URL, followed by registration to the completion event, and releasing the thread. You could almost think this is Node.Js! What actually took me the longest time to develop and debug was JSONP itself. The information I found about it, and jQuery’s client-side support was a little tricky to find, and I spent a few hours struggling with overly escaped JSON and other fun stuff. After that was done, I simply pushed it to github, registered the whateverorigin.org domain for a measly $7 a year, and replaced anyorigin.com with whateverorigin.org in Bitcoin Pie’s code, and voila – the site was back online. I really like developing websites in 2011 – there are entire industries out there that have set out to make it easy for individuals / small startups to build amazing products. Reference: WhateverOrigin – Combat the Same Origin Policy with Heroku and Play! Framework from our JCG partner Ron Gross at the A Quantum Immortal blog...

if – else coding style best practices

The following post is going to be an advanced curly-braces discussion with no right or wrong answer, just more “matter of taste”. It is about whether to put “else” (and other keywords, such as “catch”, “finally”) on a new line or not.             Some may write if (something) { doIt(); } else { dontDoIt(); }I, however, prefer if (something) { doIt(); } else { dontDoIt(); }That looks silly, maybe. But what about comments? Where do they go? This somehow looks wrong to me: // This is the case when something happens and blah // blah blah, and then, etc... if (something) { doIt(); } else { // This happens only 10% of the time, and then you // better think twice about not doing it dontDoIt(); }Isn’t the following much better? // This is the case when something happens and blah // blah blah, and then, etc... if (something) { doIt(); }// This happens only 10% of the time, and then you // better think twice about not doing it else { dontDoIt(); }In the second case, I’m really documenting the “if” and the “else” case separately. I’m not documenting the call to “dontDoIt()”. This can go further: // This is the case when something happens and blah // blah blah, and then, etc... if (something) { doIt(); }// Just in case else if (somethingElse) { doSomethingElse(); }// This happens only 10% of the time, and then you // better think twice about not doing it else { dontDoIt(); }Or with try-catch-finally: // Let's try doing some business try { doIt(); }// IOExceptions don't really occur catch (IOException ignore) {}// SQLExceptions need to be propagated catch (SQLException e) { throw new RuntimeException(e); }// Clean up some resources finally { cleanup(); }It looks tidy, doesn’t it? As opposed to this: // Let's try doing some business try { doIt(); } catch (IOException ignore) { // IOExceptions don't really occur } catch (SQLException e) { // SQLExceptions need to be propagated throw new RuntimeException(e); } finally { // Clean up some resources cleanup(); }I’m curious to hear your thoughts… References:  if – else coding style best practices from our JCG partner Lukas Eder at the JAVA, SQL, AND JOOQ blog....

REST Pagination in Spring

This is the seventh of a series of articles about setting up a secure RESTful Web Service using Spring 3.1 and Spring Security 3.1 with Java based configuration. This article will focus on the implementation of pagination in a RESTful web service. The REST with Spring series:Part 1 – Bootstrapping a web application with Spring 3.1 and Java based Configuration Part 2 – Building a RESTful Web Service with Spring 3.1 and Java based Configuration Part 3 – Securing a RESTful Web Service with Spring Security 3.1 Part 4 – RESTful Web Service Discoverability Part 5 – REST Service Discoverability with Spring Part 6 – Basic and Digest authentication for a RESTful Service with Spring Security 3.1Page as resource vs Page as representation The first question when designing pagination in the context of a RESTful architecture is whether to consider the page an actual resource or just a representation of resources. Treating the page itself as a resource introduces a host of problems such as no longer being able to uniquely identify resources between calls. This, coupled with the fact that outside the RESTful context, the page cannot be considered a proper entity, but a holder that is constructed when needed makes the choice straightforward: the page is part of the representation. The next question in the pagination design in the context of REST is where to include the paging information:in the URI path: /foo/page/1 the URI query: /foo?page=1Keeping in mind that a page is not a resource, encoding the page information in the URI is no longer an option. Page information in the URI query Encoding paging information in the URI query is the standard way to solve this issue in a RESTful service. This approach does however have one downside – it cuts into the query space for actual queries: /foo?page=1&size=10 The Controller Now, for the implementation – the Spring MVC Controller for pagination is straightforward: @RequestMapping( value = "admin/foo",params = { "page", "size" },method = GET ) @ResponseBody public List< Foo > findPaginated( @RequestParam( "page" ) int page, @RequestParam( "size" ) int size, UriComponentsBuilder uriBuilder, HttpServletResponse response ){ Page< Foo > resultPage = service.findPaginated( page, size ); if( page > resultPage.getTotalPages() ){ throw new ResourceNotFoundException(); } eventPublisher.publishEvent( new PaginatedResultsRetrievedEvent< Foo > ( Foo.class, uriBuilder, response, page, resultPage.getTotalPages(), size ) ); return resultPage.getContent(); }The two query parameters are defined in the request mapping and injected into the controller method via @RequestParam; the HTTP response and the Spring UriComponentsBuilder are injected in the Controller method to be included in the event, as both will be needed to implement discoverability. Discoverability for REST pagination Withing the scope of pagination, satisfying the HATEOAS constraint of REST means enabling the client of the API to discover the next and previous pages based on the current page in the navigation. For this purpose, the Link HTTP header will be used, coupled with the official “next“, “prev“, “first” and “last” link relation types. In REST, Discoverability is a cross cutting concern, applicable not only to specific operations but to types of operations. For example, each time a Resource is created, the URI of that resource should be discoverable by the client. Since this requirement is relevant for the creation of ANY Resource, it should be dealt with separately and decoupled from the main Controller flow. With Spring, this decoupling is achieved with events, as was thoroughly discussed in the previous article focusing on Discoverability of a RESTful service. In the case of pagination, the event – PaginatedResultsRetrievedEvent – was fired in the Controller, and discoverability is achieved in a listener for this event: void addLinkHeaderOnPagedResourceRetrieval( UriComponentsBuilder uriBuilder, HttpServletResponse response, Class clazz, int page, int totalPages, int size ){ String resourceName = clazz.getSimpleName().toString().toLowerCase(); uriBuilder.path( "/admin/" + resourceName ); StringBuilder linkHeader = new StringBuilder(); if( hasNextPage( page, totalPages ) ){ String uriNextPage = constructNextPageUri( uriBuilder, page, size ); linkHeader.append( createLinkHeader( uriForNextPage, REL_NEXT ) ); } if( hasPreviousPage( page ) ){ String uriPrevPage = constructPrevPageUri( uriBuilder, page, size ); appendCommaIfNecessary( linkHeader ); linkHeader.append( createLinkHeader( uriForPrevPage, REL_PREV ) ); } if( hasFirstPage( page ) ){ String uriFirstPage = constructFirstPageUri( uriBuilder, size ); appendCommaIfNecessary( linkHeader ); linkHeader.append( createLinkHeader( uriForFirstPage, REL_FIRST ) ); } if( hasLastPage( page, totalPages ) ){ String uriLastPage = constructLastPageUri( uriBuilder, totalPages, size ); appendCommaIfNecessary( linkHeader ); linkHeader.append( createLinkHeader( uriForLastPage, REL_LAST ) ); } response.addHeader( HttpConstants.LINK_HEADER, linkHeader.toString() ); }In short, the listener logic checks if the navigation allows for a next, previous, first and last pages and, if it does, adds the relevant URIs to the Link HTTP Header. It also makes sure that the link relation type is the correct one – “next”, “prev”, “first” and “last”. This is the single responsibility of the listener (the full code here). Test Driving Pagination Both the main logic of pagination and discoverability should be extensively covered by small, focused integration tests; as in the previous article, the rest-assured library is used to consume the REST service and to verify the results. These are a few example of pagination integration tests; for a full test suite, check out the github project (link at the end of the article): @Test public void whenResourcesAreRetrievedPaged_then200IsReceived(){ Response response = givenAuth().get( paths.getFooURL() + "?page=1&size=10" ); assertThat( response.getStatusCode(), is( 200 ) ); } @Test public void whenPageOfResourcesAreRetrievedOutOfBounds_then404IsReceived(){ Response response = givenAuth().get( paths.getFooURL() + "?page=" + randomNumeric( 5 ) + "&size=10" ); assertThat( response.getStatusCode(), is( 404 ) ); } @Test public void givenResourcesExist_whenFirstPageIsRetrieved_thenPageContainsResources(){ restTemplate.createResource(); Response response = givenAuth().get( paths.getFooURL() + "?page=1&size=10" ); assertFalse( response.body().as( List.class ).isEmpty() ); }Test Driving Pagination Discoverability Testing Discoverability of Pagination is relatively straightforward, although there is a lot of ground to cover. The tests are focused on the position of the current page in navigation and the different URIs that should be discoverable from each position: @Test public void whenFirstPageOfResourcesAreRetrieved_thenSecondPageIsNext(){ Response response = givenAuth().get( paths.getFooURL()+"?page=0&size=10" );String uriToNextPage = extractURIByRel( response.getHeader( LINK ), REL_NEXT ); assertEquals( paths.getFooURL()+"?page=1&size=10", uriToNextPage ); } @Test public void whenFirstPageOfResourcesAreRetrieved_thenNoPreviousPage(){ Response response = givenAuth().get( paths.getFooURL()+"?page=0&size=10" ); String uriToPrevPage = extractURIByRel( response.getHeader( LINK ), REL_PREV ); assertNull( uriToPrevPage ); } @Test public void whenSecondPageOfResourcesAreRetrieved_thenFirstPageIsPrevious(){ Response response = givenAuth().get( paths.getFooURL()+"?page=1&size=10" ); String uriToPrevPage = extractURIByRel( response.getHeader( LINK ), REL_PREV ); assertEquals( paths.getFooURL()+"?page=0&size=10", uriToPrevPage ); } @Test public void whenLastPageOfResourcesIsRetrieved_thenNoNextPageIsDiscoverable(){ Response first = givenAuth().get( paths.getFooURL()+"?page=0&size=10" ); String uriToLastPage = extractURIByRel( first.getHeader( LINK ), REL_LAST ); Response response = givenAuth().get( uriToLastPage ); String uriToNextPage = extractURIByRel( response.getHeader( LINK ), REL_NEXT ); assertNull( uriToNextPage ); }These are just a few examples of integration tests consuming the RESTful service. Getting All Resources On the same topic of pagination and discoverability, the choice must be made if a client is allowed to retrieve all the Resources in the system at once, or if the client MUST ask for them paginated. If the choice is made that the client cannot retrieve all Resources with a single request, and pagination is not optional but required, then several options are available for the response to a get all request. One option is to return a 404 (Not Found) and use the Link header to make the first page discoverable: Link=<http://localhost:8080/rest/api/admin/foo?page=0&size=10>; rel=”first“, <http://localhost:8080/rest/api/admin/foo?page=103&size=10>; rel=”last“ Another option is to return redirect – 303 (See Other) – to the first page of the pagination. A third option is to return a 405 (Method Not Allowed) for the GET request. REST Paginag with Range HTTP headers A relatively different way of doing pagination is to work with the HTTP Range headers – Range, Content-Range, If-Range, Accept-Ranges – and HTTP status codes – 206 (Partial Content), 413 (Request Entity Too Large), 416 (Requested Range Not Satisfiable). One view on this approach is that the HTTP Range extensions were not intended for pagination, and that they should be managed by the Server, not by the Application. Implementing pagination based on the HTTP Range header extensions is nevertheless technically possible, although not nearly as common as the implementation discussed in this article. Conclusion This article covered the implementation of Pagination in a RESTful service with Spring, discussing how to implement and test Discoverability. For a full implementation of pagination, check out the github project. If you read this far, you should follow me on twitter here. Reference: REST Pagination in Spring from our JCG partner Eugen Paraschiv at the baeldung blog...

Public key infrastructure

Some time ago I was asked to create presentation for my colleagues which describes Public Key Infrastructure, its components, functions, how it generally works, etc. To create that presentation, I’ve collected some material on that topic and it would be just dissipation to throw it out. That presentation wasn’t technical at all, and that post is not going to be technical as well. It will give just a concept, high-level picture, which, I believe, can be a good base knowledge before start looking at details. I will start with cryptography itself. Why do we need it? There are at least three reasons for that – Confidentiality, Authentication and Integrity. Confidentiality is the most obvious one. It’s crystal clear that we need cryptography to hide information from others. Authentication confirms that message is send by subject which we can identify and our claims about it are true. And finally, Integrity ensures that message wasn’t modified or corrupted during transfer process.We may try to use Symmetric Cryptography to help us to achieve our aims. It uses just one shared key, which is also called secret. The secret is used for encryption and for decryption of data. Let’s have a look how it can help us to archive our aims. Does it encrypt messages? Yes. Well, Confidentiality is solved, as soon as nobody else, except communicating parties, knows the secret. Does it provide Authentication? Mmm… I would say, no. If there are just two parties in conversation, is seems ok, but if there are hundreds, then should be hundreds secrets, which is hard to manage and distribute. What about Integrity? Yes, it works fine – it’s very hard to modify encrypted message. As you can guess, symmetric cryptography has one big problem – and that problem is “shared secret”. These two words… they don’t even fit one to other. If something is known by more that one person, it is not a secret any more. Moreover, to be shared, that secret somehow has to be transferred and during that process there are too many way for secret to be stolen. This means that such type of cryptography hardly solves our problems. But it is still in use and works quite well for its purposes. It’s very fast and can be used for encryption/decryption of big amounts of data, e.g. you hard drive. Also, as far as it hundreds or even thousands times faster that asymmetric cryptography, it’s used in hybrid schemas (like TLS aka SSL), where asymmetric cryptography is used for just for transferring symmetric key and encryption/decryption is done by symmetric algorithm. Let’s have a look at Asymmetric Cryptography. It was invented very recently about 40 years ago. The first paper (“New Directions in Cryptography”) was published in 1976 by Whitfield Diffie and Martin Hellman. Their work was influenced by Ralph Merkle, who believed to be the one who created the idea of Public Key Cryptography in 1974 (http://www.merkle.com/1974/) and suggested it as project to his mentor – Lance Hoffman, who rejected it. “New Directions in Cryptography” describes algorithm of key exchange known as “Diffie–Hellman key exchange”. Interesting fact that the same key exchange algorithm was invented earlier, in 1974 in Government Communication Headquarters, UK by Malcolm J. Williamson, but that information was classified and fact was disclosed just in 1997.Asymmetric Cryptography uses pair of keys – one Private Key and one Public Key. Private Key has to be kept secret and not shared with anybody. Public Key can be available to public; it doesn’t need to be secret. Information encrypted with public key can be decrypted only with corresponding private key. As far as Private Key is not shared, there is no need to distribute it, and there is reasonably small chance that it will be compromised. So such way of exchanging information can solve Confidentiality problem. What about Authentication and Integrity? These problems are solvable as well and utilise mechanism called Digital Signature. The simplest variant if Digital Signature can use following scenario – subject creates a hash based on message, encrypt that hash with Private Key and attach it to message. Now if recipient wants to verify the subject who created a message, he will encrypt that hash using subject’s public key (that’s Authentication) and compare it with hash generated on recipient side (Integrity). In reality hash is not exactly encrypted, instead it used in special signing algorithm, but the overall concept is the same. It’s important to notice that in Asymmetric Cryptography each pair of keys serves just one purpose, e.g. if pair is used for signing, it can’t be used for encryption. Digital Signature, also, is the base for Digital Certificate AKA Public Key Certificate. Certificate is pretty much the same as your passport. It has identity information, which is similar to name, date of birth, etc. in passport. Owner of certificate has to have Private Key which matches Public Key stored in certificate, similar passport has photo of the owner, which matches owner’s face. And, finally, certificate has a signature, and its meaning is the same, as meaning of stamp in passport. Signature proves that certificate was issued by organization which made that signature. In Public Key Infrastructure world such organizations are called Certificate Authorities. If one system discovers that Certificate is signed by “trusted” Certificate Authority, it means that system will trust to information in certificate. Last paragraph may not be obvious, especially “trust” part of it. What does “trust” mean in that context? Let have a look at simple example. Every site on Web which makes a use of encrypted connection does it via TLS (SSL) protocol, which is based on Certificates. When you go to https://www.amazon.co.uk and it sends its certificate back to your browser. In that certificate there is information about website and reference to Certificate Authority who signed that certificate. First browser will look at the name in certificate – it has to be exactly the same as website domain name, in our case, that’s “www.amazon.co.uk”. Then browser will verify that certificate is signed by Trusted Certificate Authority, which is VeriSing in case of Amazon. You browser already has a list of Certificate Authorities (this is just a list of certificates with public keys) which are known as trusted ones, so it can verify that certificate is issued by one of them. There are some other verification steps, that these two are the most important ones. Assume in our case verification was successful (if it’s not browser will show is big red warning message, like that one) – certificate has proper name in it and was signed by Trusted Certificate Authority. What does it give to us? Just one thing – we know that we are on www.amazon.co.uk and the server behind that name is Amazon server, not some dodgy website, which just looks like Amazon. When we enter our credit card details and we can be relatively sure that they will be sent to Amazon, but not to hacker’s database. Our hope here based on assumption that such Certificate Authorities like VeriSign do not give dodgy certificates and Amazon server is not compromised. Well, better than nothing J Another example are severs in organization, which use certificates to verify that they can trust one to other. The schema there is very similar to browser’s ones, except two differences:Mutual authentication. Certificates are, usually, verified but both sides, not just by client. Client has to send his certificate to server. Certificate Authority, is hosted inside the company.When CA is inside the company we can be almost sure that certificates are going to be issued only to properly validated subjects. It gives some confidence that hacker can’t inject his server, even if he has access to network infrastructure. Attack is possible only if CA is compromised or some server’s Private Key is compromised.We already know, Certificate Authority is the organization which issues certificate and in the Internet, an example of such organization is VeriSing. If certificate is created to be used just inside organization (intranet), it can be issued by Information Security Department which can act as Certificate Authority. When someone wants to have certificate, he has to send certificate request which is called Certificate Signing Request to Certificate Authority. That certificate consists of subject’s identity information, subject’s public key and signature, created by subject’s private key to ensure, that subject who sent request has appropriate private key. Before signing Certificate Authority passes that request to Registration Authority who verifies all details, ensures that proper process is followed, etc. It’s possible that Certificate Authority can also act as Registration Authority. After all, if everything is ok, Certificate Authority creates new certificate signed by its private key and send it back to subject which requested certificate.I’ve already mentioned Certificate validation process. Here are some details of it; worth mentioning theirs details are still high-level. Validation consists of several steps which, broadly speaking can be described as:Certificate data validation – validity date, presence of required fields, their values, etc. Verify that certificate is issued by Trusted Certificate Authority. If you are browsing internet that list if already built-in in your browser. If that’s communication between two systems, each system has a list of trusted Certificate Authorities; usually that is just a file with certificates. Certificate’s signature is valid and made by Certificate Authority who signed that certificate. Verify that certificate is not revoked. Key verification – proves that servers can decode messaged encrypted by certificate’s Public Key.Mentioned above certificate revocation can happen because of many reasons – certificate could be compromised, or, in corporate world, employee, which owned certificate, left company, or sever which had certificate was decommissioned, etc. On order to verify certificate revocation, browser or any other piece of software, has to use one or both of following techniques:Certificate Revocation List (CRL). That’s just a file, which can be hosted on http server. It contains list of revoked certificate IDs. That’s method is simple and straightforward, it doesn’t require lots of efforts for implementation, but has three disadvantages – that’s just a file, which means, that it’s not real-time, it can use significant network traffic and it’s not checked by default by the most of the browsers (I would even say by all browsers), even if certificate has a link to CRL. Online Certificate Status Protocol (OCSP). That is preferable solution, which utilizes dedicated server, which implements protocol which will return back revocation status of certificate by its id. If browser (at least FireFox > v.3.0) will find link to that server in certificate, it will make a call to verify that certificate is not revoked. Only disadvantage is that OCSP server has to be very reliable and be able to answer on requests all the time.In internet certificate usually contains links to CRL or OCSP inside it. When certificates are used in corporate network these links are usually known by all parties and there is no need to have them in certificate. So, finally, what is Public Key Infrastructure? That’s infrastructure, which supports everything which was described above and generally consists of following elements:Subscribers. Users of certificates. Clients and ones who owns certificates. Certificates. Certificate Authority and Registration Authority. Certificate Revocation Infrastructure. Server with Certificate Revocation list or OCSP Server. Certificate Policy and Practices documents. Describe format of certificate, format of certificate request, when certificated have to be revoked, etc. Basically all procedures related to infrastructure. Hardware Security Modules, which are usually used to protect Root CA’s private key.And that entire infrastructure support following functions, which we’ve just discussed:Public Key Cryptography. Certificate issuance. Certificate validation. Certificate revocation.And that’s it. Appeared to be not such a big topic ;) References:  Public key infrastructure from our JCG partner Stanislav Kobylansky at the Stas’s blog ....

Streaming Files from MongoDB GridFS

Not too long ago I tweeted what I felt was a small triumph on my latest project, streaming files from MongoDB GridFS for downloads (rather than pulling the whole file into memory and then serving it up). I promised to blog about this but unfortunately my specific usage was a little coupled to the domain on my project so I couldn’t just show it off as is. So I’ve put together an example node.js+GridFS application and shared it on github and will use this post to explain how I accomplished it. GridFS module First off, special props go to tjholowaychuk who responded in the #node.js irc channel when I asked if anyone has had luck with using GridFS from mongoose. A lot of my resulting code is derived from an gist he shared with me. Anyway, to the code. I’ll describe how I’m using gridfs and after setting the ground work illustrate how simple it is to stream files from GridFS. I created a gridfs module that basically accesses GridStore through mongoose (which I use throughout my application) that can also share the db connection created when connecting mongoose to the mongodb server. mongoose = require "mongoose" request = require "request"GridStore = mongoose.mongo.GridStore Grid = mongoose.mongo.Grid ObjectID = mongoose.mongo.BSONPure.ObjectIDWe can’t get files from mongodb if we cannot put anything into it, so let’s create a putFile operation. exports.putFile = (path, name, options..., fn) -> db = mongoose.connection.db options = parse(options) options.metadata.filename = name new GridStore(db, name, "w", options).open (err, file) -> return fn(err) if err file.writeFile path, fnparse = (options) -> opts = {} if options.length > 0 opts = options[0] if !opts.metadata opts.metadata = {} optsThis really just delegates to the putFile operation that exists in GridStore as part of the mongodb module. I also have a little logic in place to parse options, providing defaults if none were provided. One interesting feature to note is that I store the filename in the metadata because at the time I ran into a funny issue where files retrieved from gridFS had the id as the filename (even though a look in mongo reveals that the filename is in fact in the database). Now the get operation. The original implementation of this simply passed the contents as a buffer to the provided callback by calling store.readBuffer(), but this is now changed to pass the resulting store object to the callback. The value in this is that the caller can use the store object to access metadata, contentType, and other details. The user can also determine how they want to read the file (either into memory or using a ReadableStream). exports.get = (id, fn) -> db = mongoose.connection.db id = new ObjectID(id) store = new GridStore(db, id, "r", root: "fs" ) store.open (err, store) -> return fn(err) if err # band-aid if "#{store.filename}" == "#{store.fileId}" and store.metadata and store.metadata.filename store.filename = store.metadata.filename fn null, storeThis code just has a small blight in that it checks to see if the filename and fileId are equal. If they are, it then checks to see if metadata.filename is set and sets store.filename to the value found there. I’ve tabled the issue to investigate further later. The Model In my specific instance, I wanted to attach files to a model. In this example, let’s pretend that we have an Application for something (job, a loan application, etc) that we can attach any number of files to. Think of tax receipts, a completed application, other scanned documents. ApplicationSchema = new mongoose.Schema( name: String files: [ mongoose.Schema.Mixed ] ) ApplicationSchema.methods.addFile = (file, options, fn) -> gridfs.putFile file.path, file.filename, options, (err, result) => @files.push result @save fnHere I define files as an array of Mixed object types (meaning they can be anything) and a method addFile which basically takes an object that at least contains a path and filename attribute. It uses this to save the file to gridfs and stores the resulting gridstore file object in the files array (this contains stuff like an id, uploadDate, contentType, name, size, etc). Handling Requests This all plugs in to the request handler to handle form submissions to /new. All this entails is creating an Application model instance, adding the uploaded file from the request (in this case we named the file field “file”, hence req.files.file) and saving it. app.post "/new", (req, res) -> application = new Application() application.name = req.body.name opts = content_type: req.files.file.type application.addFile req.files.file, opts, (err, result) -> res.redirect "/"Now the sum of all this work allows us to reap the rewards by making it super simple to download a requested file from gridFS. app.get "/file/:id", (req, res) -> gridfs.get req.params.id, (err, file) -> res.header "Content-Type", file.type res.header "Content-Disposition", "attachment; filename=#{file.filename}" file.stream(true).pipe(res)Here we simply look up a file by id and use the resulting file object to set Content-Type and Content-Disposition fields and finally make use of ReadableStream::pipe to write the file out to the response object (which is an instance of WritableStream). This is the piece of magic that streams data from MongoDB to the client side. Ideas This is just a humble beginning. Other ideas include completely encapsulating gridfs within the model. Taking things further we could even turn the gridfs model into a mongoose plugin to allow completely blackboxed usage of gridfs. Feel free to check the project out and let me know if you have ideas to take it even further. Fork away! Reference: Streaming Files from MongoDB GridFS from our JCG partner James Carr at the Rants and Musings of an Agile Developer blog...

Arquillian with NetBeans, GlassFish embedded, JPA and a MySQL Datasource

This is an, let’s call it accidental post. I was looking into transactional CDI observers and playing around with GlassFish embedded to run some integration tests against it. But surprisingly this did not work too well and I am still figuring out, where exactly the problems are while using the plain embedded GlassFish for that. In the meantime I switched to Arquillian. After I looked at the Arquillian 1.0.0.Alpha4 a bit more detailed last year, it was time to see, what the guys prepared for 1.0.0 final. Some stuff changed a bit and I was surprised to only find some basic examples on the net. That was the main reason I started writing this post. To have a more complete example of all the three technologies working together. Getting Started First of all, get yourself a fresh copy of latest NetBeans 7.1. It’s out since a few weeks and it really looks good. If you like, you can download a copy of the Java EE version, which comes with latest GlassFish OSS Edition 3.1.1 pre bundled. Install it and fire it up. Also grep a copy of MySQL Community Edition and install it. Back in NetBeans, setup a new Maven Webapplication via the new Project Wizard. Let’s call it “simpleweb” and we tell it to run on GF 3.1.1 (if you haven’t done so, you should create a Services>Server>GlassFish instance before or do it during the project setup). Implement your Application Even if this isn’t test-driven, I like to use this approach because I still believe, that this is the most common case you find out there in your projects. You have a lot of stuff ready to run and you are looking for some kind of automated integration tests. So, let’s assume you have a very basic entity, we call it “com.mycompany.simpleweb.entities.AuditLog”. You can create it with the NetBeans new Entity wizard. The third step during the Entity creation is the provider and database setup. Define a new Datasource and name it “jdbc/auditlog”. As a connection specification use MySQL J driver and I assume you have a database up and running (let’s assume this is called auditlog). Test the connection and finish the wizard.If you are using the wizard, you get some free gifts. Beside the fact, that you now have your AuditLog entity in the source tree, you also find a META-INF/persistence.xml file in your src/main/resources and a glassfish-resources.xml in src/main/setup. This is needed later on, keep it in mind. Add some additional properties to your entity. For now I add “String account”. And don’t forget to define a Version field “Timestamp timestamp”. And it’s also nice to have a little named query to get a list of all AuditLogs @NamedQuery(name = "findAllAuditLogs", query = "SELECT OBJECT (e) FROM AuditLog e") @Version private Timestamp timestamp;If you are using the wizard, make sure to check your pom.xml. The wizard is adding some eclipselink dependencies in scope provided, so this shouldn’t make a big difference here. Next is to add a com.mycompany.simpleweb.service.AuditRepositoryService EJB. This should be responsible for all CRUD operations on the AuditLog entity. Add some code to it to insert an AuditLog: @PersistenceContext private EntityManager em; public void writeLog(String account) { AuditLog log = new AuditLog(); log.setAccount(account); em.persist(log); }And some more code to find out the total number of entries in your table: public int findAll() { TypedQuery<AuditLog> query = em.createNamedQuery("AuditLog.findAllAuditLogs", AuditLog.class); return query.getResultList().size(); } That’s all for now. Adding Basic Test Dependencies Next we are going to add some very basic test dependencies. Open your projects pom.xml file and add the following sections for Arquillian to your project: <repository> <id>JBoss</id> <name>JBoss Repository</name> <url>https://repository.jboss.org/nexus/content/groups/public/</url> </repository> <dependencymanagement> <dependencies> <dependency> <groupid>org.jboss.arquillian</groupid> <artifactid>arquillian-bom</artifactid> <version>1.0.0.Final-SNAPSHOT</version> <scope>import</scope> <type>pom</type> </dependency> </dependencies> </dependencymanagement> <dependencies> <dependency> <groupid>org.jboss.arquillian.container</groupid> <artifactid>arquillian-glassfish-embedded-3.1</artifactid> <version>1.0.0.Final-SNAPSHOT</version> <scope>test</scope> </dependency> <dependency> <groupid>org.jboss.arquillian.junit</groupid> <artifactid>arquillian-junit-container</artifactid> <scope>test</scope> </dependency> </dependencies>Beside that, you also need the embedded Glassfish dependency. <dependency> <groupid>org.glassfish.extras</groupid> <artifactid>glassfish-embedded-all</artifactid> <version>3.1</version> <scope>test</scope> </dependency>We also need the MySQL J driver: <dependency> <groupid>mysql</groupid> <artifactid>mysql-connector-java</artifactid> <version>5.1.18</version> <scope>test</scope> </dependency>Configuring Arquillian After we have all the needed dependencies in place, we need to further configure Arquillian. This is done via the arquillian.xml which has to be placed in the src/test/resources folder (you might need to create it outside NetBeans before) and should look like this: <arquillian xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://jboss.org/schema/arquillian http://jboss.org/schema/arquillian/arquillian-1.0.xsd"> <engine> <property name="deploymentExportPath">target/arquillian</property> </engine> <container default="true" qualifier="glassfish"> <configuration> <property name="sunResourcesXml">src/main/setup/glassfish-resources.xml</property> </configuration> </container> </arquillian>The engine parameter tells Arquillian to place a packaged version of your test archive to a target/arquillian folder. This is quite useful for hunting down problems. The container qualifier points the testrunner to the glassfish-resources.xml which was created by the entity creation wizard. All done. One single thing I would like to suggest is to make a copy of your persistence.xml and place it to the test/resources folder renamed to something like test-persistence.xml. I consider it a best practice to have an option to configure your test JPA a bit different than the productive one. To make a simple example, we would like to see some more logging output during the tests, so the copied version should additionally contain the needed parameters. I also like to change the table generation strategy for testing to drop-and-create-tables: <property name="eclipselink.ddl-generation" value="drop-and-create-tables" /> <property name="eclipselink.logging.level.sql" value="FINEST" /> <property name="eclipselink.logging.parameters" value="true" />Let’s take a look at the the tests. Add a Testcase Lets add a test. This is easy with NetBeans: Right click on your EJB and select “Tools>Create JUnit Tests”. Select JUnit 4.x and accept the name proposal “com.mycompany.simpleweb.service.AuditRepositoryServiceTest”. Now your project has a new “Test Packages” folder. As you can see, the test is in error. NetBeans assumes, that you want to do a test based on embedded EJBContainer. Nice guess, but we would like to add some Arquillian here. Remove the EJBContainer import and strip the class down to this: @RunWith(Arquillian.class) public class AuditRepositoryServiceTest { }Now it’s time to define the deployment archive for the test using ShrinkWrap. The deployment archive for the test is defined using a static method annotated with Arquillian’s @Deployment annotation. @Deployment public static JavaArchive createTestArchive() { return ShrinkWrap.create(JavaArchive.class, "test.jar").addPackage(AuditLog.class.getPackage()).addPackage(AuditRepositoryService.class.getPackage()).addAsManifestResource( new ByteArrayAsset("<beans>".getBytes()), ArchivePaths.create("beans.xml")).addAsManifestResource( "test-persistence.xml", ArchivePaths.create("persistence.xml")); } After the packages which should be contained are added, an empty beans.xml (which should be enough for now) is added and the test-persistence.xml is added as a manifest resource named persistence.xml. Great. One last thing is to define the test itself. @EJB AuditRepositoryService repository; @Test public void insertLog() throws Exception { repository.writeLog("Markus"); int numberOfLogs = repository.findAll(); Assert.assertEquals(1, numberOfLogs); }We are inserting a simple test entity and are getting the count back from the database which is checked via assertEquals. That’s all. Fire up your tests. (Right click on the AuditRepositoryServiceTest class and select “Test File (Strg+F6). Examining what’s happening The output window shows the Std.out of a starting GlassFish. If you examine the output further you see, that the JDBC connection pool and the JDBC resource are created: INFO: command add-resources result: PlainTextActionReporterSUCCESSDescription: add-resources AdminCommandnull JDBC connection pool mysql_auditlog_rootPool created successfully. JDBC resource jdbc/auditlog created successfully. and the “test” application was deployed: INFO: WEB0671: Loading application [test] at [/test] 17.01.2012 10:12:39 org.glassfish.deployment.admin.DeployCommand execute INFO: test was successfully deployed in 6.461 milliseconds. Scanning through the output does point you to some EclipseLink stuff, but the additional sql logging doesn’t seem to be in effect. This is because EclipseLink needs to know to which logger to point the output to. Normally the log output is redirected to the server logger which is auto-discovered. We didn’t do any logging configuration until now and simply rely on what is default for Java Logging. So, let’s add a little logging configuration. Put an empty logging.properties file to src/test/resources and add some simple lines to it: handlers=java.util.logging.ConsoleHandler java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter java.util.logging.ConsoleHandler.level=FINEST add the maven sure-fire plugin to the build section of your pom.xml: <plugin> <groupid>org.apache.maven.plugins</groupid> <artifactid>maven-surefire-plugin</artifactid> <version>2.11</version> <configuration> <includes> <include>com/mycompany/simpleweb/service/*</include> </includes> <systempropertyvariables> <java.util.logging.config.file>${basedir}/src/test/resources/logging.properties</java.util.logging.config.file> </systempropertyvariables> </configuration> </plugin>If you now issue a clean and build, you see, that the desired log output is shown in the NetBeans build output. FEIN: INSERT INTO AUDITLOG (ID, ACCOUNT, TIMESTAMP) VALUES (?, ?, ?) bind => [1, Markus, 2012-01-17 11:02:54.0] In fact, if you use Strg+F6 you still only see INFO level messages. To fix this, you need to change your NetBeans run action settings. Right click your project and select “Properties”. Select “Actions” and “Test file”. Add the following as a new line within “Set Properties” area: java.util.logging.config.file=src/test/resources/logging.propertiesNow you also see the desired log-level output with a single test-run. That was it. You can download the complete sample maven project (as ZIP-File) with the mentioned classes and play around a bit. Have fun! Even if the above post was intended to be a more complex demo it turns out, that I missed a big issue with the setup. Everything works fine up to the point when you start introducing enhanced features to your entities. To name but a few: lazy loading, change tracking, fetch groups and so on. JPA providers like to call this “enhancing” and it is most often referred to as “weaving”. Weaving is a technique of manipulating the byte-code of compiled Java classes. The EclipseLink JPA persistence provider uses weaving to enhance JPA entities for the mentioned things and to do internal optimizations. Weaving can be performed either dynamically at runtime, when Entities are loaded, or statically at compile time by post-processing the Entity .class files. Dynamic weaving is mostly recommended as it is easy to configure and does not require any changes to a project’s build process. You may have seen some finer log output from EclipseLink like the following: [...]–Begin weaver class transformer processing class [com/mycompany/simpleweb/entities/AuditLog]. [...]–Weaved persistence (PersistenceEntity) [com/mycompany/simpleweb/entities/AuditLog]. [...]–Weaved change tracking (ChangeTracker) [com/mycompany/simpleweb/entities/AuditLog]. [...]–Weaved lazy (ValueHolder indirection) [com/mycompany/simpleweb/entities/AuditLog]. [...]–Weaved fetch groups (FetchGroupTracker) [com/mycompany/simpleweb/entities/AuditLog]. [...]–End weaver class transformer processing class [com/mycompany/simpleweb/entities/AuditLog]. The problem with Arquillian and Embedded GlassFish Imagine you take the example from yesterday’s blog post and change the simple String account property to something like this: @ManyToOne(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY) private Person person;That’s exactly one of the mentioned cases where your JPA provider would need to do some enhancements to your class files before executing. Without modifying the project it would lead to some very nasty exceptions: Exception Description: A NullPointerException would have occurred accessing a non-existent weaved _vh_ method [_persistence_get_person_vh]. The class was not weaved properly – for EE deployments, check the module order in the application.xml deployment descriptor and verify that the module containing the persistence unit is ahead of any other module that uses it. [...] Internal Exception: java.lang.NoSuchMethodException: com.mycompany.simpleweb.entities.AuditLog._persistence_get_person_vh() Mapping: org.eclipse.persistence.mappings.ManyToOneMapping[person] Descriptor: RelationalDescriptor(com.mycompany.simpleweb.entities.AuditLog –> [DatabaseTable(AUDITLOG)]) at org.eclipse.persistence.exceptions.DescriptorException.noSuchMethodWhileInitializingAttributesInMethodAccessor(DescriptorException.java:1170) at org.eclipse.persistence.internal.descriptors.MethodAttributeAccessor.initializeAttributes(MethodAttributeAccessor.java:200) [...] indicating that something is missing. And that missing method is introduced by the weaving process. If you decompile a weaved entity you can see what the JPA provider is complaining about. This is how your enhanced entity class should look like. And this is only one of the enhanced methods a weaving process is introducing into your code. public WeavedAttributeValueHolderInterface _persistence_get_person_vh() { _persistence_initialize_person_vh(); if(_persistence_person_vh.isCoordinatedWithProperty() || _persistence_person_vh.isNewlyWeavedValueHolder()) { Person person1 = _persistence_get_person(); if(person1 != _persistence_person_vh.getValue()) _persistence_set_person(person1); } return _persistence_person_vh; }Dynamic vs. Static Weaving Obviously the default dynamic weaving doesn’t work with the described setup. Why? Weaving is a spoiled child. It only works when the entity classes to be weaved do exist only in the application classloader. The combination of embedded GlassFish, Arquillian and the maven sure-fire-plugin mix this up a bit and the end of the story is, that exactly none of your entities are enhanced at all. Compare this nice discussion for a more detailed explanation. If dynamic waving doesn’t work, we have to use the fallback called static weaving. Static means: post processing the entities during the build. Having the maven project at hand, this sounds like a fairly easy job. Let’s look for something like this. The first thing you probably find is the StaticWeaveAntTask. The second thing may be Craig’s eclipselink-staticweave-maven-plugin. Let’s start with the StaticWeaveAntTask. You would have to use maven-antrunner-plugin to get this introduced. Copy classes from left to right and do an amazing lot of wrangling to get your classpath rigth. Laird Nelson did a great job to archetype-ize an example configuration for all 3 big JPA providers (EclipseLink, OpenJPA, Hibernate) and your could give this a try. A detailed explanation about what is happening can be found on his blog. Thanks Laird for the pointers! Don’t get me wrong: This is a valid approach, but I simply don’t like it. Mainly because it introduces a massive complexity to the build and having seen far too many projects without the right skills for managing even normal maven projects, this simply isn’t a solution for me. I tried the static weaving plugin done by Craig Day. Adding static weaving to simpleweb So, let’s open the pom.xml from yesterdays project and introduce the new plugin: <plugin> <artifactId>eclipselink-staticweave-maven-plugin</artifactId> <groupId>au.com.alderaan</groupId> <version>1.0.1</version> <executions> <execution> <goals> <goal>weave</goal> </goals> <phase>process-classes</phase> </execution> </executions> </plugin>Done. Now your classes are weaved and if you introduce some logging via the plugin configuration you can actually see, what happens to your entity classes. The plugin is available via repo1.maven.org. The only issue I came across is, that the introduced dependency towards EclipseLink 2.2.0 isn’t (or course) not available via the same repo, so you probably would need to build it for yourself with the right repositories and dependencies. You can get the source code via the plugin’s google code page. Don’t forget to add the weaving property to your test-persistance.xml: <property name="eclipselink.weaving" value="static" />[UPDATE: 19.01.2012] Craig released a new 1.0.2 version of the plugin which solves the issues with the EclipseLink dependency. You now can simply include the needed EclipseLink version as a dependency to the plugin. Also needed is the correct EclipseLink maven repository. A complete example with a configured log level looks like this: <repository> <id>eclipselink</id> <name>Repository hosting the eclipselink artifacts</name> <url>http://www.eclipse.org/downloads/download.php?r=1&nf=1&file=/rt/eclipselink/maven.repo/</url> </repository> [...] <plugin> <artifactId>eclipselink-staticweave-maven-plugin</artifactId> <groupId>au.com.alderaan</groupId> <version>1.0.2</version> <executions> <execution> <goals> <goal>weave</goal> </goals> <phase>process-classes</phase> <configuration> <logLevel>ALL</logLevel> </configuration> </execution> </executions> <dependencies> <dependency> <groupId>org.eclipse.persistence</groupId> <artifactId>eclipselink</artifactId> <version>2.3.1</version> </dependency> </dependencies> </plugin>References:  Arquillian with NetBeans, GlassFish embedded, JPA and a MySQL Datasource & Arquillian with NetBeans, GlassFish embedded, JPA and a MySQL Datasource – Part II from our JCG partner Markus Eisele at the Enterprise Software Development with Java blog....

Tips for Testing Database Code

Almost everybody understands that source code belongs into version control. Many people understand we need to test our code. Quite a few do that automatically. But everything seems to change when it comes to databases. A lot of stuff in and around databases goes untested. Heck some of the scripts don’t even live in version control. If you can’t believe that, because you haven’t seen it, you are a damn lucky bastard. At least one reason for this state of affairs is obviously: It hurts. Database tests tend to be slow, interdependent and hard to maintain. Granted. But you know what: If it hurts, you should do it more often. It will teach you what exactly the things are that cause pain when testing and eventually you’ll find approaches to make it less painful. Here are some ideas I found helpful when testing database related code:Give every developer her own database. This forces you to find a way to set up the database fast, easy and reliable. If your application lives in a single user/schema/namespace it is sufficient for each developer to have his own user/schema/namespace in a single database. For this to work though … … the application should be user/schema/namespace agnostic. It makes it much easier to create multiple instances one a single server. Let the application live in a single user/schema/namespace. If you have multiple interdependent namespaces (e.g. for modules) you’ll have a hard time making them agnostic of the names. Have separate instances for CI, Demos, QA and so on. Actually ideally it should be trivial to create a fresh instance. Stay away from any tool that comes with its own repository. If have seen about a dozen of such tools and although some looked promising in the beginning, they all completely failed to integrate with other tools on the development side of things. Examples of such tools are tools for code generation from UML or ER models and ETL tools.The previous points where about the setup of your database and infrastructure. Lets have a look at the code:Favor a proper Language (like Java, C, PHP …) over database specific languages like T-SQL or PL/SQL. If you are wondering why, make a comparison between your favorite DB language and your all purpose language. For which do you get the better IDE, Unit testing support, code analysis, code coverage and so on. Reconsider your main language if it doesn’t win in that comparison. Have a small layer that does all interaction with the database. Make sure no SQL or other database dependent code leaks out. Inject that layer as a dependency into anybody in need of it. This will allow you to test almost everything without worrying about the database. Only the tests for that integration layer actually needs a database for testing. Favor database independent SQL or a library abstracting away the differences of various databases. Back in the time people claimed they needed that in case they have to switch database vendors, which never happened. Now it does. See below.The next points will deal with the actual tests:Consider an in-memory-database for testing. Many databases can run in an in-memory-mode. They are great for testing, because you can throw them away after the test, and they are way faster then any database writing to disk. This of course is only possible when you work with a database system that can run as a in-memory-database or if your code is database independent. Hence the previous point. If you can’t use your database as in memory database, consider putting it on a RAM disk. We got a huge performance gain for our tests with this approach. A solid state disk might be the next best thing although I’m not sure how it would react to the heavy load of continuous database tests. Make test failure messages so explicit that you don’t have to look into the database for analyzing test failures. Use code for setting up your test data. Make it nice and concise. If you need a row in a table without special requirements for its values you should be able to create that with a single trivial line of code, no matter how many foreign keys the table contains. I.e. you should have a little DSL for your test data. Doing it with plain code will enable all the refactoring power of your IDE for your tests. For load and performance tests other approaches like loading production data or large amounts of generated data might be suitable. Make sure your tests clean up after them selves. There are two approaches I found usable in most cases:Recreate the schema for every test. This is slow but really safe. Do a rollback after each test. This only works when there is no commit inside the test. The mean thing is: If a test tries to rollback, but fails because there was a commit inside the test some completely different test will fail. It can be a really frustrating task to find the bad test in such a case.We covered the testing of database related code inside your application. But there is another kind of code we need to deal with: Scripts for deploying your application (or upgrading it)The scripts that change your database schema from one version to the next are source code just like everything else. Therefore they belong under version control and should get tested continuously. The testing process is really simple: Create a database as it looks now. Apply your change scripts and verify it looks as desired. For verifying the resulting schema it is useful to have a script that creates your target database (or at least the schema) from scratch, so you compare it with the result of the test. For performance reasons you might want to test this with an empty database first. But don’t forget to run it on an instance with realistic data as well. Hint: adding a column to huge tables can take loooooong.Happy testing everybody. Reference: Tips for Testing Database Code from our JCG partner Jens Schauder at the Schauderhaft blog...
Java Code Geeks and all content copyright © 2010-2014, Exelixis Media Ltd | Terms of Use | Privacy Policy
All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners.
Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries.
Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation.
Do you want to know how to develop your skillset and become a ...
Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you two of our best selling eBooks for FREE!

Get ready to Rock!
You can download the complementary eBooks using the links below: