INTERVIEW QUESTIONS J2EE EJB DETAILS

Question: What is the lifecycle of Entity Bean

Answer: The following steps describe the life cycle of an entity bean instance

An entity bean instances life starts when the container creates the instance using newInstance and then initialises it using setEntityContext.

The instance enters the pool of available instances. Each entity bean has its own pool. While the instance is in the available pool, the instance is not associated with any particular entity object identity. Any of these pooled instances may be used to execute finder (ejbFind) or home (ejbHome) methods.

An instance transitions from the pooled state to the ready state when the container selects that instance to service a client call to an entity object. There are two possible transitions from the pooled to the ready state: through the creation of an entity (ejbCreate and ejbPostCreate) or through the activation of an entity (ejbActivate).
When an entity bean instance is in the ready state, the instance is associated with a specific entity object identity. While the instance is in the ready state, the container can synchronize the instance with its representation in the underlying data source whenever it determines the need to using ejbLoad and ejbStore methods. Business methods can also be invoked zero or more times on an instance. An ejbSelect method can be called by a business method, ejbLoad or ejbStore method.
The container can choose to passivate an entity bean instance within a transaction. To passivate an instance, the container first invokes the ejbStore method to allow the instance to prepare itself for the synchronization of the database state with the instance’s state, and then the container invokes the ejbPassivate method to return the instance to the pooled state.
There are three possible transitions from the ready to the pooled state: through the ejbPassivate method, through the ejbRemove method (when the entity is removed), and because of a transaction rollback for ejbCreate, ejbPostCreate,or ejbRemove.
The container can remove an instance in the pool by calling the unsetEntityContext() method on the instance.

The following steps describe the life cycle of an entity bean instance

An entity bean instances life starts when the container creates the instance using newInstance and then initialises it using setEntityContext.

The instance enters the pool of available instances. Each entity bean has its own pool. While the instance is in the available pool, the instance is not associated with any particular entity object identity. Any of these pooled instances may be used to execute finder (ejbFind) or home (ejbHome) methods.

An instance transitions from the pooled state to the ready state when the container selects that instance to service a client call to an entity object. There are two possible transitions from the pooled to the ready state: through the creation of an entity (ejbCreate and ejbPostCreate) or through the activation of an entity (ejbActivate).
When an entity bean instance is in the ready state, the instance is associated with a specific entity object identity. While the instance is in the ready state, the container can synchronize the instance with its representation in the underlying data source whenever it determines the need to using ejbLoad and ejbStore methods. Business methods can also be invoked zero or more times on an instance. An ejbSelect method can be called by a business method, ejbLoad or ejbStore method.
The container can choose to passivate an entity bean instance within a transaction. To passivate an instance, the container first invokes the ejbStore method to allow the instance to prepare itself for the synchronization of the database state with the instance’s state, and then the container invokes the ejbPassivate method to return the instance to the pooled state.
There are three possible transitions from the ready to the pooled state: through the ejbPassivate method, through the ejbRemove method (when the entity is removed), and because of a transaction rollback for ejbCreate, ejbPostCreate,or ejbRemove.
The container can remove an instance in the pool by calling the unsetEntityContext() method on the instance. Source: CoolInterview.com

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