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What it gives you that is completely missing in EJB 3.0 and prior versions is the ability to have an EJB that is notified when the application starts and notified when the application stops. So you can do all sorts of things that you previously could only do with a load-on-startup servlet. It also gives you a place to hold data that pertains to the entire application and all users using it, without the need for a static. Additionally, Singleton beans can be invoked by several threads at one time similar to a Servlet.

See the Singleton Beans page for a full description of the javax.ejb.Singleton api.

The Code

PropertyRegistryBean

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The end result is that the threading model for this bean will switch from multi-threaded access to single-threaded access dynamically as needed depending on the which methods are being invoked. This gives Singletons a bit of an advantage over Servlets for processing multi-threaded requests.

See the Singleton Beans page for more advanced details on Container-Managed Concurrency.

Test Case

{snippet:url=openejb3/examples/simple-singleton/src/test/java/org/superbiz/registry/ComponentRegistryBeanTest.java|lang=java|id=code}

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