## Service POJOS via the deployment descriptor

Service POJOs allow you to define POJOs as JBoss services. The way you define them is very similar to how you define stateless or stateful session beans. One very important difference is that there will only ever be ONE instance of the service bean. i.e. it is not pooled - the bean instance is a singleton. The singleton bean contains shared state, so data set by one client is accessible by other clients.

### Example simple ServicePOJO

Take a look at ServiceOne.java and the corresponding deployment descriptor jboss.xml. The `service` tag defines it as a singleton service in JBoss. It implements ServiceOneRemote and ServiceOneLocal just as you would do for a normal stateful/stateless bean using the `remote` and `local` tags.

ServiceOne also implements ServiceOneManagement.java identified through the `management` tag. JBoss will inspect this interface, and create and install an MBean implementing the attributes and operations defined in the interface. The MBean will work on the same singleton bean instance as the remote and local interfaces.

The default ObjectName used for a service bean is

`jboss.j2ee:jar=<jar file name>service=EJB3,name=<Name of @Service bean>,type=<Interface>`

So in our case it will be `jboss.j2ee:jar-tutorial.jar,service=EJB3,name=ServiceOne,type=ManagementInterface`

Note that the default ObjectName can be overriden as is the case with ServiceTwo.java through the `object-name` tag.

### Building

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

In the JBoss console you should see output similar to this when the .jar archive is deployed

    16:52:30,326 INFO  [Ejb3Module] found EJB3 service bean: org.jboss.tutorial.service.bean.ServiceOne
    16:52:30,387 INFO  [Ejb3Module] found EJB3 service bean: org.jboss.tutorial.service.bean.ServiceThree
    16:52:30,397 INFO  [Ejb3Module] found EJB3 service bean: org.jboss.tutorial.service.bean.ServiceTwo
    16:52:30,427 INFO  [ProxyDeployer] no declared remote bindings
    16:52:30,437 INFO  [ProxyDeployer] there is remote interfaces
    16:52:30,437 INFO  [ProxyDeployer] default remote binding has jndiName of org.jboss.tutorial.service.bean.ServiceOneRemote
    16:52:35,113 INFO  [STDOUT] ServiceOne - Creating
    16:52:35,113 INFO  [STDOUT] ServiceOne - Starting
    16:52:35,244 INFO  [ProxyDeployer] no declared remote bindings
    16:52:35,945 INFO  [STDOUT] ServiceTwo - Starting
    16:52:35,965 INFO  [ProxyDeployer] no declared remote bindings
    16:52:36,585 INFO  [STDOUT] ServiceThree - Starting
    16:52:36,585 INFO  [EJB3Deployer] Deployed: file:/C:/cygwin/home/Kab/cvs/jboss-head/build/output/jboss-5.0.0alpha/server/all/deploy/tutorial.jar

ServiceOne starts before ServiceTwo which starts before ServiceThree, due to the dependencies we set up earlier.

Then to run the example

    $ ant run
    Buildfile: build.xml

    run:
         [java] attribute value for singleton obtained via JMX is what we set via remote i/f: 100
         [java] Hello from service One
         [java] Hello from service Two

The JBoss console should show the following output

    17:05:07,796 INFO  [STDOUT] ServiceThree - Interceptor
    17:05:07,796 INFO  [STDOUT] ServiceThree - Calling ServiceOne.sayHello() via JMX server
    17:05:07,806 INFO  [STDOUT] ServiceThree - Interceptor
    17:05:07,806 INFO  [STDOUT] ServiceThree - Calling ServiceTwo.sayHello() via MBean proxy

Notice that the calls to the ServiceThree methods get intercepted.