The life of an entity bean

The life of an entity bean

 

There are three distinct states in the life cycle of an entity enterprise bean:

 

v Nonexistent

v Pooled

v Ready

 

 

The nonexistent state

 

At first the entity bean instance doesn't exist. The EJB container creates an instance of an entity bean and then it calls the setEntityContext() method on the entity bean to pass the instance a reference to its context; that is, a reference to the EntityContext interface. The EntityContext interface gives the instance access to container provided services and allows it to obtain information about its clients. The entity bean is now in the pooled state.

 

The pooled state

 

Each type of entity bean has its own pool. None of the instances in the pool are associated with data. Because none of their instance variables have been set, the instances have no identity and they are all equivalent.

 

The container is free to assign any instance to a client that requests such an entity bean. When a client application calls one of the entity bean's finder methods, the container executes the corresponding ejbFind() method on an arbitrary instance in the pool. The instance remains in the pooled state during the execution of a finder method. When the container selects an instance to service a client's requests to an entity object, that instance moves from the pooled to the ready state.

 

There are two ways that an entity instance moves from the pooled state to the ready state:

v Through the ejbCreate() and ejbPostCreate() methods.

v Through the ejbActivate() method.

 

The container selects the instance to handle a client's request on the bean's home interface. In response to the create() call , the container creates an entity object and calls the ejbCreates() and ejbPostCreate() methods when the instance is assigned to the entity object. The container calls the ejbActivate() method to activate an instance so that it can respond an invocation on an existing entity object. Usually the container calls ejbActivate() when there is no suitable instance in the ready state to handle the client's calls.

 

The ready state

 

When the instance is in the ready state, it is associated with a specific primary key. Clients can call the application specific methods on the entity bean. The container calls the ejbLoad() and ejbStore() methods to tell the bean to load and store its data. They also enable the bean instance to synchronize its state with that of the underlying data entity.

 

Returning to the pooled state

 

When an entity bean instance moves back to the pooled state , the instance is decoupled from the data represented by the entity. The container can now assign the instance of any entity object within the same entity bean home. There are two ways a entity bean instance moves from the ready state back to the pooled state:

 

ü  The container calls the ejbPassivate() methods to disassociate the instance from its primary key without removing the underlying entity object.

ü The container calls the ejbRemove() method to remove the entity object. It calls ejbRemove() when the client application calls the bean's home or remote remove() method.

 

To remove an unassociated instance from the pool, the container calls the instance's unsetEntityContext() method.