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Simple Stateful Example
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Overview

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This example shows how to create a Stateful session EJB using annotations.

A Stateful session bean is a session bean whose instances can maintain the conversational state with the client. The conversational state of the stateful session bean, which describes the conversation between a specific client and a session bean, is contained in the fields of the stateful session bean.

Simply put, when you create a stateful bean an actual instance is created by the container and dedicated to you and only you. Every call you make will go to your instance. Further, your instance will not be shared with anyone unless you give them a reference to your stateful bean. The instance will last until you remove it or until it times-out and is removed by the container.

With EJB 3.0, it's now possible to write stateful session bean without specifying a deployment descriptor; you basically have to write just a remote or local business interface, which is a plain-old-java-interface, annotated with the @Remote or @Local annotation the stateful session bean implementation, a plain-old-java-object which implements the remote or the local business interface and is annotated with the @Stateful annotation

This example is the "simple-stateful" example located in the openejb-examples.zip available on the download page.

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The Code

In this example we develop a simple counter stateful session EJB. Every stateful session bean implementation must be annotated using the annotation @Stateful or marked that way in the ejb-jar.xml file.

Bean

:id=code|url=openejb3/examples/simple-stateful/src/main/java/org/superbiz/counter/CounterImpl.java|lang=java}

In EJB 3.0 session beans do not need to implement the javax.ejb.SessionBean interface. You can simply annotate it as @Stateful if you want it to be a stateful session bean.

Users of EJB 2.x may notice the bean actually implements the business interfaces! In the prior version of EJB implementing the remote interface (which derives from javax.ejb.EJBObject) in your bean was just not allowed. Now there is no javax.ejb.EJBObject requirement, so implementing the business interfaces is standard practice for EJB 3.0.

Local business interface

:id=code|url=openejb3/examples/simple-stateful/src/main/java/org/superbiz/counter/CounterLocal.java|lang=java}

Local interfaces in EJB are pass-by-reference interfaces. Meaning that normal java semantics are used for passing arguments, return values and exceptions. A business local interface can be any plain java interface. There are no restrictions on the method arguments, return types, or throws clauses.

Unless specified otherwise, every interface your bean implements (and it's parent class implements and so on) is considered to be a local business interface. You can use the @Local annotation to explicitly state that an interface is a local interface, but this is not required.

You'll notice that in EJB 3.0 the Local Business Interface of a stateless session bean does not need to extend from javax.ejb.EJBLocalObject and does not need a javax.ejb.EJBLocalHome interface as they did in EJB 2.x and prior. Per the vocabulary of the EJB spec, interfaces that implement javax.ejb.EJBLocalObject or javax.ejb.EJBLocalHome are considered Component Interfaces and the plain java interface above is considered a Business Interface.

Remote business interface

:id=code|url=openejb3/examples/simple-stateful/src/main/java/org/superbiz/counter/CounterRemote.java|lang=java}

Remote interfaces are pass-by-value interfaces. Meaning that all method parameters, return values, and exceptions are serialized on every call. The result is that you get a copy of the original object and not the original object. The advantage is of course that Remote interfaces can be used to invoke an EJB across a network in a client-server fashion. There are no restrictions on the Remote interface itself, but there are on the data passed in and out of the remote interface. The values passed into a method or returned from a method of a Remote interface must be serializable. It is fine for the method signature to be, for example, "public Object myMethod(Object myParam)" as long as the value passed in and returned implements java.io.Serializable.

As stated above, the Remote Business Interface of a bean can be any plain old interface. It does not need to extend javax.ejb.EJBObject, it does not need a javax.ejb.EJBHome, the methods do not need to throw javax.rmi.RemoteException, and the bean class can implement it!

At minimum the interface must be annotated with @Remote either in the interface itself or in the bean class, or the interface must be declared via in the ejb-jar.xml.

Writing a unit test for the example

Writing an unit test for the stateful session EJB is quite simple. We need just to write a setup method to create and initialize the InitialContext, and then write our test methods

setUp

:id=setup|url=openejb3/examples/simple-stateful/src/test/java/org/superbiz/counter/CounterImplTest.java|lang=java}

Test the local business interface

:id=local|url=openejb3/examples/simple-stateful/src/test/java/org/superbiz/counter/CounterImplTest.java|lang=java}

Test the remote business interface

:id=remote|url=openejb3/examples/simple-stateful/src/test/java/org/superbiz/counter/CounterImplTest.java|lang=java}
:title=JNDI Names} Note that JNDI names for Java SE clients are not standardized by the EJB spec. This is unfortunate and something being addressed in EJB 3.1. The default schema that OpenEJB uses is ejbName + interfaceType (i.e. Local, Remote, LocalHome, RemoteHome), so in our example "CounterImpl" + "Local" and "CounterImpl" + "Remote". You can in fact change this default to be absolutely anything you want including interface class name, ejb class name, and more.
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Running

Running the example is fairly simple. In the "simple-stateful" directory of the examples zip , just run:

$ mvn clean install

Which should create output like the following.

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running org.superbiz.counter.CounterImplTest
Apache OpenEJB 3.0    build: 20080408-04:13
http://tomee.apache.org/
INFO - openejb.home =

/Users/dblevins/work/openejb-3.0/examples/simple-stateful INFO - openejb.base = /Users/dblevins/work/openejb-3.0/examples/simple-stateful INFO - Configuring Service(id=Default Security Service, type=SecurityService, provider-id=Default Security Service) INFO - Configuring Service(id=Default Transaction Manager, type=TransactionManager, provider-id=Default Transaction Manager) INFO - Configuring Service(id=Default JDK 1.3 ProxyFactory, type=ProxyFactory, provider-id=Default JDK 1.3 ProxyFactory) INFO - Found EjbModule in classpath: /Users/dblevins/work/openejb-3.0/examples/simple-stateful/target/classes INFO - Configuring app: /Users/dblevins/work/openejb-3.0/examples/simple-stateful/target/classes INFO - Configuring Service(id=Default Stateful Container, type=Container, provider-id=Default Stateful Container) INFO - Auto-creating a container for bean CounterImpl: Container(type=STATEFUL, id=Default Stateful Container) INFO - Loaded Module: /Users/dblevins/work/openejb-3.0/examples/simple-stateful/target/classes INFO - Assembling app: /Users/dblevins/work/openejb-3.0/examples/simple-stateful/target/classes INFO - Jndi(name=CounterImplLocal) --> Ejb(deployment-id=CounterImpl) INFO - Jndi(name=CounterImplRemote) --> Ejb(deployment-id=CounterImpl) INFO - Created Ejb(deployment-id=CounterImpl, ejb-name=CounterImpl, container=Default Stateful Container) INFO - Deployed Application(path=/Users/dblevins/work/openejb-3.0/examples/simple-stateful/target/classes) Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.698 sec

Results :

Tests run: 2, Failures: 0, Errors: 0, Skipped: 0

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