Startup / Shutdown Callbacks in EJB 3.1
Every now and then you need to know when your application starts/stops so that you can perform some action. For years now this has been supported in Java by the Servlet Specification and its ServletContextListener class. Unfortunately this functionality was never offered by the EJB specification. With the release of EJB 3.1 and the @Singleton annotation, this functionality is now possible, and the code is much cleaner and simpler. Here is an example:
import javax.ejb.Singleton;
import javax.ejb.Startup;
@Startup
@Singleton
public class FooBean {
@PostConstruct
void onStartup() {
// Startup Stuff..
}
@PreDestroy
void onShutdown() {
// Shutdown Stuff..
}
}As you can see, the code is very simple and straight forward. There is no configuration needed. Just annotate your class/methods and the container will do the rest.
The @Startup annotation will cause the Singleton to initialize eagerly during the application startup sequence. Once all the injection has taken place, the container will call the bean's @PostConstruct method. Since the bean is container managed, you have access to all other EJB components, JPA EntityManagers, the TimerService, etc. And unlike other EJB component types, any container-managed transaction behavior for the bean applies to the @PostConstruct method as well.
By defining a @PreDestroy method the bean instance can request a shutdown notification. Since the Singleton bean instance life cycle is tied to the container's life cycle, this method will be called when the application is shutting down.