Tag Archives: ejb

Use of generics in EJB 3.1

With EJB 3.1 it is possible to make use of generics in your bean implementations. There are some aspects that needs to be considered though to make sure you use them as intended. It requires basic understanding of how Java generics work.

Imagine the following scenario. You might want to have a business interface such as:

public interface Async<TYPE> {
    public void method(TYPE t);

… and an implementation:

public class AsyncBean implements Async<String> {
    public void method(final String s) {}

You would then like to dependency inject your EJB into another bean such as:

@EJB Async<String> asyncBean;

A problem here is that due to type erasure, you cannot be certain that the injected EJB is of the expected type which will produce a ClassCastException in runtime. Another problem is that the method annotated with @Asynchronous in the bean implementation will not be invoked asynchronously as might be expected. This is due to the method not actually being part of the business interface. The method in the business interface is in fact public void method(final Object s) due to type erasure, which in turn calls the typed method. Therefore the call to the typed method won’t be intercepted and made asynchronous. If the type definition in the AsyncBean class is removed (infers Object type), the call will be asynchronous. One solution to ensure type safety would be to treat the Async interface as a plain interface without the @Local annotation, mark the AsyncBean with @LocalBean (to make sure the bean method is part of the exposed business methods for that bean), and inject an AsyncBean where used. Another solution would be to insert a local interface between the plain interface and the bean implementation:

public interface AsyncLocal extends Async<String> {
    public void method(final String s);

… and then make the AsyncBean implement the AsyncLocal interface instead, and use the AsyncLocal interface at the injection points.

This behaviour might not be all that obvious, even though it makes perfect sense due to how generics are treated in Java. It is also unfortunate that the EJB specification does not clarify the expected behaviour for this use case. The following can be read in the specification, which feels a bit vague:
“3.4.3 Session Bean’s Business Interface
The session bean’s interface is an ordinary Java interface. It contains the business methods of the session bean.”

I’ve created a minimal sample project where the behaviours can be tried out by just running a simple test case written with Arquillian. The test case will be run inside an embedded TomEE container. Thanks to the blazing speed of TomEE, the test runs just as fast as a unit test. The code can be found here, and contains a failing test representing the scenario described above. Apply the proposed soultion to make the test pass.

As demonstrated, there are some caveats which needs to be considered when using generics together with EJBs. Hopefully this article can shed some light on what is happening under the hood.

Tommy Tynjä

Writing integration tests in Java with Arquillian

Arquillian is a JBoss project that focuses on integration testing for Java. It’s an Open Source project I’m contributing to and using on the current project I’m working on. It let’s you write integration tests just as you would write unit tests, but it adds some very important features into the mix. Arquillian actually lets you execute your test cases inside a target runtime, such as your application server of choice! It also lets you make use of dependency injection to let you test your services directly in your integration test. Arquillian comes with a whole bunch of adapters to different runtimes, such as JBoss 7,6,5, Glassfish 3, Weld, WebSphere and even Selenium. So if you’re working with a common runtime, it is probably already supported! If your runtime is not supported, you could contribute with an adapter for it! What Arquillian basically needs to know is how to manage your runtime, how to start and stop the runtime and how to do deployments and undeployments. Just put the adapter for your runtime on your classpath and Arquillian will handle the rest.

Let’s get down to business. What does an Arquillian test look like? Image that we have a very basic EJB which we want to integration test:

public class WeekService {
  public String weekOfYear() {
      return Integer.toString(Calendar.getInstance().get(Calendar.WEEK_OF_YEAR));

This EJB provides one single method which returns what week of the year it is. Sure, we could just as well unit test the functionality of this EJB, but imagine that we might want to extend this bean with more functionality later on and that we want to have a proper integration test already in place. What would an Arquillian integration test look like that asserts the behaviour of this bean? With JUnit, it would look something like this:

public class WeekServiceTest {

    public static Archive deployment() {
        return ShrinkWrap.create(JavaArchive.class, "week.jar")

    @EJB WeekService service;

    public void shouldReturnWeekOfYear() {
        Assert.assertEquals("" + Calendar.getInstance().get(Calendar.WEEK_OF_YEAR),

The first thing you notice is the @RunWith annotation at the top. This tells JUnit to let Arquillian manage the test. The next thing you notice is the static method that is annotated with @Deployment. This method creates a Java Archive (jar) representation containing the WeekService class which we want to test. The archive is created using ShrinkWrap, which let’s you assemble archives through a fluent Java API. Arquillian will take this archive and deploy it to the target runtime before executing the test cases, and will after the test execution undeploy the same archive from the runtime. You are not forced to have a deployment method, as you might as well want to test something that is already deployed or available in your runtime. If you have a runtime that is already running somewhere, you can setup Arquillian to run in remote mode, which means that Arquillian expects the runtime to already be running, and just do deployments and undeployments in the current environment. You could also tell Arquillian to run in managed mode, where Arquillian expects to be able to start the runtime before the test execution, and will also shutdown the runtime when the test execution completes. Some runtimes also comes with an embedded mode, which means that Arquillian will run an own isolated runtime instance during the test execution.

Probably the biggest difference to a standard unit test in the above example is the @EJB annotation on the WeekService property. This actually lets you specify that you want an EJB dependency injected into your test case when executing your tests, and Arquillian will handle that for you! If you want to make sure that is the case, just remove the @EJB annotation and you will indeed get a NullPointerException when calling service.weekOfYear() in your test method. A feature which is going to be added to a feature version of Arquillian is to fail fast if dependencies can’t be fullfilled (instead of throwing NPE’s).

The @Test annotated method handles the actual test logic, just like a unit test. The difference here is that the test is actually executed within your target runtime!

This was just a basic example of what you can do with Arquillian. The more you work with it, the more you will start to recognize different use cases where integration tests becomes a natural way of testing the intended behaviour.

The full source code of the above example is available on GitHub: https://github.com/tommysdk/showcase/tree/master/arquillian/. It also contains a more sophisticated example which uses CDI and JPA within an integration test. The examples runs on a JBoss 7.0.2 runtime, which comes bundled with the example. For more details and a deeper dive into Arquillian, visit the project website at http://arquillian.org.


Tommy Tynjä

An introduction to Java EE 6

Enterprise Java is really taking a giant leap forward with its latest specification, the Java EE 6. What earlier required (more or less) third party frameworks to achieve are now available straight out of the box in Java EE. EJB’s for example have gone from being cumbersome and complex to easy and lightweight, without compromises in functionality. For the last years, every single project I’ve been working on has in one way or another incorporated the Spring framework, and especially the dependency injection (IoC) framework. One of the best things with Java EE 6 in my opinion is that Java EE now provides dependency injection straight out of the box, through the CDI (Context and Dependency Injection) API. With this easy to use, standardized and lightweight framework I can now see how many projects can actually move away from being dependent on Spring just for this simple reason. CDI is not enabled by default and to enable it you need to put a beans.xml file in the META-INF/WEB-INF folder of your module (the file can be empty though). With CDI enabled you can just inject your dependencies with the javax.inject.Inject annotation:

public class MyArbitraryEnterpriseBean {

   private MyBusinessBean myBusinessBean;


Also note that the above POJO is actually a stateless session bean thanks to the @Stateless annotation! No mandatory interfaces or ejb-jar.xml are needed.

Working with JSF and CDI is just as simple. Imagine that you have the following bean, where the javax.inject.Named annotation marks it as a CDI bean:

public class ControllerBean {

   public void happy() { ... }

   public void sad() { ... }

You could then invoke the methods from a JSF page like this:

<h:form id="controllerForm">
      <h:commandButton value=":)" action="#{controller.happy}"/>
      <h:commandButton value=":(" action="#{controller.sad}"/>

Among other nice features of Java EE 6 is that EJB’s are now allowed to be packaged inside a war package. That alone can definitely save you from packaging headaches. Another step in making Java EE lightweight.

If you are working with servlets, there are good news for you. The notorious web.xml is now optional, and you can declare a servlet as easy as:

public class MyServlet extends HttpServlet {

To start playing with Java EE 6 with the use of Maven, you could just do mvn archetype:generate and select one of the jee6-x archetypes to get yourself a basic Java EE 6 project structure, e.g. jee6-basic-archetype.

Personally I believe Java EE 6 is breaking new grounds in terms of enterprise Java. Java EE 6 is what J2EE was not, e.g. easy, lightweight, flexible, straightforward and it has a promising future. Hopefully Java EE will from now on be the natural choice when building applications, over the option of depending on a wide selection of third party frameworks, which has been the case in the past.


Tommy Tynjä