Dependency Injection in JBoss 4.2: Hold Your Excitement

For the last little while I have been pushing my company to migrate our Enterprise Beans to EJB3 (most of our beans are of the 2.1 variety) and Dependency Injection (DI) has been one of the EJB3 features that I have been very excited to see getting used throughout our middle tier.

DI is a great new addition to the EJB spec which gives the ability to ‘inject’ an EJB reference in another bean simply by using the @EJB annotation:

@EJB
MyBeanInterface myBeanReference;

At run-time, the container populates the field with the appropriate bean reference, thus saving the developer some manual JNDI lookup code. For a more thorough discussion of DI, check out Debu Panda’s article.

The biggest selling point for us was that EJB references can also be injected with a bean setter methods, e.g.

@EJB
void setMyBean(MyBeanInterface myBean){
this.myBean = myBean;
}

which can make a bean easily unit-testable with the setter used to pass in a mock object during the test set up.

However when we started using DI with the latest stable version of JBoss (4.2.2) we found that DI of EJB references has limited support. Namely it is only supported for objects inside the EJB container. This means that while beans can refer to each other with the @EJB annotation, other managed objects like servlets and non-EJB web services must still use JNDI lookup to access any Enterprise Beans.

To quote from the JBoss docs:

“JBoss Application Server 4.2.2 implemented EJB3 functionality by way of an EJB MBean container running as a plugin in the JBoss Application Server. This had certain implications for application development. The EJB3 plugin injects references to an EntityManager and @EJB references from one EJB object to another. However this support is limited to the EJB3 MBean and the JAR files it manages. Any JAR files which are loaded from a WAR (such as Servlets, JSF backing beans, and so forth) do not undergo this processing”

So even though the JEE 5 specification stipulates a wider scope of the @EJB annotation, JBoss 4.2.2 doesn’t support it. In fact JBoss 4.2.2 is a ‘bridge’ version that doesn’t claim full JEE 5 compliance. And while I am grateful for the many other JEE 5 features JBoss currently does provide, I hope this post saves people out there the time and effort of trying in vain to make @EJB references work for servlets, web services or other WAR components.