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30.4.4. Pluggable Interceptors and Locking Policy
We saw that the basic entity bean lifecycle and behavior is defined by the container configuration defined in
standardjboss.xml descriptor. Let us look at the container-interceptors definition for the Standard CMP 2.x EntityBean configuration.
<container-interceptors>
<interceptor>org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.LogInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.SecurityInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.TxInterceptorCMT</interceptor>
<interceptor>org.jboss.ejb.plugins.CallValidationInterceptor</interceptor>
<interceptor metricsEnabled="true">org.jboss.ejb.plugins.MetricsInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.EntityCreationInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.EntityLockInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.EntityInstanceInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.EntityReentranceInterceptor</interceptor>
<interceptor>org.jboss.resource.connectionmanager.CachedConnectionInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.EntitySynchronizationInterceptor</interceptor>
<interceptor>org.jboss.ejb.plugins.cmp.jdbc.JDBCRelationInterceptor</interceptor>
</container-interceptors>
The interceptors shown above define most of the behavior of the entity bean. Below is an explanation of the interceptors that are relevant to this section.
- EntityLockInterceptor: This interceptor's role is to schedule any locks that must be acquired before the invocation is allowed to proceed. This interceptor is very lightweight and delegates all locking behavior to a pluggable locking policy.
- EntityInstanceInterceptor: The job of this interceptor is to find the entity bean within the cache or create a new one. This interceptor also ensures that there is only one active instance of a bean in memory at one time.
- EntitySynchronizationInterceptor: The role of this interceptor is to synchronize the state of the cache with the underlying storage. It does this with the
ejbLoadandejbStoresemantics of the EJB specification. In the presence of a transaction this is triggered by transaction demarcation. It registers a callback with the underlying transaction monitor through the JTA interfaces. If there is no transaction the policy is to store state upon returning from invocation. The synchronization polices A, B and C of the specification are taken care of here as well as the JBoss specific commit-option D.
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