WebLogic: The Definitive Guide

Configuring Entity Beans

The life cycle of an entity bean is a hybrid of the life cycles of a stateless and a stateful session bean. WebLogic maintains a free pool of inactive entity EJB instances. Just like stateless session beans, you can set the initial and the maximum sizes for the EJB pool. If you do specify a value for the initial-beans-in-free-pool setting, WebLogic prepares the pool of EJB instances with this initial capacity when the server starts up. Each EJB instance is created using the newInstance( ) method, and the setEntityContext( ) method is invoked once it’s added to the pool. At this point, each EJB instance has a reference to the EntityContext, which provides the entity EJB with access to various container-managed services. When an EJB instance is removed from the pool, the container invokes the unsetEntityContext( ) method. In general, an entity EJB instance will remain in this pooled state as long as clients continue to invoke methods on the home object, or when the EJB container invokes one of the query methods on the entity bean.

Just like stateful session beans, WebLogic also maintains a cache of active entity EJB instances. The max-beans-in-cache element in the weblogic-ejb-jar.xml descriptor determines the maximum size of the entity cache. When a client invokes a create( ) method on the entity bean, the EJB container dips into the free pool and automatically invokes the ejbCreate( ) method on the EJB instance obtained from the pool, before placing it ...