Timer Service and Callbacks

This example shows you how to access javax.ejb.SessionContext as well as using the EJB Timer Service. It also explains how callbacks work in EJB 3.0.

SessionContext injection

The javax.ejb.SessionContext is injected using the @javax.annotation.Resource annotation. When the stateless bean instance is created the field will be initialized with the correct SessionContext. Take a look at ExampleTimerBean.java

   private @Resource SessionContext ctx;

Callbacks

The rest of the bean example registers a timer with the EJB Timer service. In the EJB 2.1 specification it was required to implement an interface to get ejbTimeout callbacks. It is still being debated in the EJB 3.0 EG on whether an interface or annotation should be used to specify this callback. In JBoss EJB 3 Preview, it is implemented as an annotation. All you have to define is a method annotated with javax.ejb.Timeout. This is the same with other callbacks like @PrePassviate, @PostRemove, etc... No interface is needed to be implemented, just declare the methods as you need them.

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Building and Running

To build and run the example, make sure you have ejb3.deployer installed in JBoss 4.0.x and have JBoss running. See the reference manual on how to install EJB 3.0.

Unix:    $ export JBOSS_HOME=<where your jboss 4.0 distribution is>
Windows: $ set JBOSS_HOME=<where your jboss 4.0 distribution is>
$ ant
$ ant run

After 5 seconds look at the JBoss console window to see the Timer being fired.

00:51:20,074 INFO  [STDOUT] ---------------------
00:51:20,074 INFO  [STDOUT] * Received Timer event: Hello World
00:51:20,074 INFO  [STDOUT] ---------------------