# Session EJB and MDB Configuration

## Pooling

Both Stateless Session beans and Message Driven Beans have an instance pool. The basic configuration of JBoss uses a thread local pool to avoid Java synchronization (org.jboss.ejb3.ThreadLocalPool). These EJB types can be configured to use an alternative pooling mechanism. For example, JBoss has a strict pool size implementation that will only allow a fixed number of concurrent requests to run at one time. If there are more requests running than the pool's strict size, those requests will block until an instance becomes available. This is configured via the @org.jboss.annotation.ejb.PoolClass annotation.

                @Retention(RetentionPolicy.RUNTIME)
                @Target({ElementType.TYPE})
                public @interface PoolClass
                {
                   Class value();
                   int maxSize() default 30;
                   long timeout()default Long.MAX_VALUE;
                }

The value() parameter defines the pool implementation class you want to plug in. maxSize() defines the size of the pool while timeout() is a time in milliseconds you want to block when waiting for an instance to be ready. This annotation can be applied to a stateless or message driven bean class. Here's an example of using it.

                @Stateless
                @PoolClass (value=org.jboss.ejb3.StrictMaxPool.class, maxSize=5, timeout=10000)
                @Remote(StrictlyPooledSession.class)
                public class StrictlyPooledSessionBean implements StrictlyPooledSession
                {
                 ...
                }

There is no nice way of applying the same configuration through XML. To do it through XML you must define a new aspect domain (an EJB container configuration template) and define an annotation override within that domain and then apply the domain through jboss.xml. Here's an example:

First create the aspect domain. Create a file called mydomain-aop.xml and put this in the top level directory of your EJB jar. Might seem a little cryptic but what this is doing is declaring an annotation that will be created by the EJB container. Our EJB3 implementation is based on JBoss AOP. See the JBoss AOP documentation for more info on annotation overrides.

    <aop>
       <domain name="Strictly Pooled Stateless Bean" extends="Stateless Bean" inheritBindings="true">
          <annotation expr="!class(@org.jboss.annotation.ejb.PoolClass)">
              @org.jboss.annotation.ejb.PoolClass (value=org.jboss.ejb3.StrictMaxPool.class, maxSize=5, timeout=10000)
          </annotation>
       </domain>
       <domain name="Strictly Pooled Message Driven Bean" extends="Message Driven Bean" inheritBindings="true">
          <annotation expr="!class(@org.jboss.annotation.ejb.PoolClass)">
              @org.jboss.annotation.ejb.PoolClass (value=org.jboss.ejb3.StrictMaxPool.class, maxSize=5, timeout=10000)
          </annotation>
       </domain>
    </aop>

There is no nice way of applying the same configuration through XML. To do it through XML you must define a new aspect domain (an EJB container configuration template) and define an annotation override within that domain and then apply the domain through jboss.xml. Here's an example:

The next thing you have to do is apply the aspect domain to your EJB within a jboss.xml file in the META-INF directory.

    <?xml version="1.0"?>
    <jboss
            xmlns="http://java.sun.com/xml/ns/javaee"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                                http://www.jboss.org/j2ee/schema/jboss_5_0.xsd"
            version="3.0">
       <enterprise-beans>
          <session>
             <ejb-name>MySessionBean</ejb-name>
             <aop-domain-name>Strictly Pooled Stateless Bean</aop-domain-name>
          </session>
       </enterprise-beans>
    </jboss>

## The Stateful Session Bean Cache

Stateful beans are stored in a cache. This cache is responsible for passivated stateful sessions when the cache becomes too full or a bean is too old. You may want to set things like the max size of this cache, and when beans should become idle. Configuration is different depending on whether you are clustered or not.

### Non-Clustered

For non clustered stateful beans, the @org.jboss.annotation.ejb.cache.simple.CacheConfig annotation is responsible for configuring the cache.

                   public @interface CacheConfig
                   {
                      int maxSize() default 100000;

                      long idleTimeoutSeconds() default 300;
                   }

If you want an XML version, you must do a similar pattern as shown in the pooling section above. You must create an aspect domain through XML and apply that domain through XML.

### Clustered

For non clustered stateful beans, the @org.jboss.annotation.ejb.cache.tree.CacheConfig annotation is responsible for configuring the cache.

                   public @interface CacheConfig
                   {
                      String name() default "jboss.cache:service=EJB3SFSBClusteredCache";

                      int maxSize() default 10000;

                      long idleTimeoutSeconds() default 300;
                   }

The name() attribute specificies the kernel name of the clustered cache you are using. Usually you won't change this value. If you want an XML version, you must do a similar pattern as shown in the pooling section above. You must create an aspect domain through XML and apply that domain through XML.

### No Passivation

Sometimes it is useful to turn off passivation entirely. This can be done by plugging in the caching implementation using the @org.jboss.annotation.ejb.cache.Cache (org.jboss.ejb3.cache.NoPassivationCache.class) annotation.