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,
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annotated
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with
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the
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@Remote
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or
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@Local
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annotation
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the
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stateful
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session
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bean
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implementation,
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a
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plain-old-java-object
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which
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implements
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the
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remote
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or
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the
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local
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business
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interface
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and
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is
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annotated
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with
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the
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@Stateful
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annotation
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This
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example
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is
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the
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"simple-stateful"
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example
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located
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in
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the
...
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available
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on
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the
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download
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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
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file.
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Bean
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In
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EJB
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3.0
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session
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beans
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do
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not
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need
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to
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implement
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the
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javax.ejb.SessionBean
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interface.
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You
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can
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simply
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annotate
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it
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as
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@Stateful
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if
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you
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want
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it
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to
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be
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a
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stateful
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session
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bean.
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Users
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of
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EJB
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2.x
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may
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notice
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the
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bean
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actually
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implements
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the
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business
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interfaces!
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In
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the
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prior
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version
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of
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EJB
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implementing
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the
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remote
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interface
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(which
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derives
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from
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javax.ejb.EJBObject)
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in
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your
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bean
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was
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just
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not
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allowed.
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Now
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there
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is
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no
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javax.ejb.EJBObject
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requirement,
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so
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implementing
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the
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business
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interfaces
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is
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standard
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practice
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for
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EJB
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3.0.
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Local
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business
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interface
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Local
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interfaces
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in
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EJB
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are
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pass-by-reference
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interfaces.
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Meaning
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that
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normal
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java
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semantics
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are
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used
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for
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passing
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arguments,
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return
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values
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and
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exceptions.
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A
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business
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local
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interface
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can
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be
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any
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plain
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java
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interface.
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There
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are
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no
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restrictions
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on
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the
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method
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arguments,
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return
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types,
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or
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throws
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clauses.
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Unless
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specified
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otherwise,
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every
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interface
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your
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bean
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implements
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(and
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it's
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parent
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class
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implements
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and
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so
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on)
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is
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considered
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to
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be
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a
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local
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business
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interface.
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You
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can
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use
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the
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@Local
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annotation
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to
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explicitly
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state
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that
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an
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interface
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is
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a
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local
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interface,
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but
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this
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is
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not
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required.
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You'll
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notice
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that
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in
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EJB
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3.0
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the
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Local
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Business
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Interface
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of
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a
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stateless
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session
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bean
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does
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not
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need
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to
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extend
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from
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javax.ejb.EJBLocalObject
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and
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does
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not
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need
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a
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javax.ejb.EJBLocalHome
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interface
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as
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they
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did
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in
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EJB
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2.x
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and
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prior.
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Per
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the
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vocabulary
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of
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the
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EJB
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spec,
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interfaces
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that
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implement
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javax.ejb.EJBLocalObject
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or
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javax.ejb.EJBLocalHome
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are
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considered
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Component
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Interfaces
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and
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the
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plain
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java
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interface
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above
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is
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considered
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a
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Business
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Interface.
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Remote
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business
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interface
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Remote
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interfaces
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are
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pass-by-value
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interfaces.
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Meaning
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that
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all
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method
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parameters,
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return
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values,
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and
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exceptions
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are
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serialized
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on
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every
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call.
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The
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result
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is
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that
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you
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get
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a
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copy
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of
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the
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original
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object
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and
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not
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the
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original
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object.
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The
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advantage
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is
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of
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course
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that
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Remote
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interfaces
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can
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be
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used
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to
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invoke
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an
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EJB
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across
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a
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network
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in
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a
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client-server
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fashion.
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There
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are
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no
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restrictions
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on
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the
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Remote
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interface
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itself,
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but
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there
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are
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on
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the
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data
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passed
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in
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and
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out
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of
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the
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remote
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interface.
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The
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values
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passed
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into
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a
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method
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or
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returned
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from
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a
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method
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of
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a
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Remote
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interface
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must
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be
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serializable
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.
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It
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is
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fine
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for
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the
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method
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signature
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to
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be,
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for
...
example,
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"public
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Object
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myMethod(Object
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myParam)"
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as
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long
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as
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the
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value
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passed
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in
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and
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returned
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implements
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java.io.Serializable
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.
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As
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stated
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above,
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the
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Remote
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Business
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Interface
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of
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a
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bean
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can
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be
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any
...
plain
...
old
...
interface.
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It
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does
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not
...
need
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to
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extend
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javax.ejb.EJBObject,
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it
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does
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not
...
need
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a
...
javax.ejb.EJBHome,
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the
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methods
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do
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not
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need
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to
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throw
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javax.rmi.RemoteException,
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and
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the
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bean
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class
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can
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implement
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it!
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At
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minimum
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the
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interface
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must
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be
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annotated
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with
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@Remote
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either
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in
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the
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interface
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itself
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or
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in
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the
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bean
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class,
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or
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the
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interface
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must
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be
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declared
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via
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<business-remote>
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in
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the
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ejb-jar.xml.
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Writing
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a
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unit
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test
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for
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the
...
example
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Writing
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an
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unit
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test
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for
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the
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stateful
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session
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EJB
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is
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quite
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simple.
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We
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need
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just
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to
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write
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a
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setup
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method
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to
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create
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and
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initialize
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the
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InitialContext,
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and
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then
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write
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our
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test
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methods
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setUp
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Test
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the
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local
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business
...
interface
...
...
Test
...
the
...
remote
...
business
...
interface
...
...
Note
...
that
...
JNDI
...
names
...
for
...
Java
...
SE
...
clients
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are
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not
...
standardized
...
by
...
the
...
EJB
...
spec.
...
This
...
is
...
unfortunate
...
and
...
something
...
being
...
addressed
...
in
...
EJB
...
3.1.
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The
...
default
...
schema
...
that
...
OpenEJB
...
uses
...
is
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ejbName
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+
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interfaceType
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(i.e.
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Local,
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Remote,
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LocalHome,
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RemoteHome),
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so
...
in
...
our
...
example
...
"CounterImpl"
...
+
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"Local"
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and
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"CounterImpl"
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+
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"Remote".
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You
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can
...
in
...
fact
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change
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this
...
default
...
to
...
be
...
absolutely
...
...
...
...
including
...
interface
...
class
...
name,
...
ejb
...
class
...
name,
...
and
...
more.
...
Running
Running the example is fairly simple. In the "simple-stateful"
...
directory
...
of
...
the
...
...
...
,
...
just
...
run:
...
$
...
mvn
...
clean
...
install
...
Which
...
should
...
create
...
output
...
like
...
the
...
following.
...
...