Just as the entity bean has a well-defined life cycle, so does the stateless session bean. The stateless session bean’s life cycle has two states: the Does Not Exist state and the Method-Ready Pool. The Method-Ready Pool is similar to the instance pool used for entity beans. This is one of the significant life-cycle differences between stateless and stateful session beans; stateless beans define instance pooling in their life cycle and stateful beans do not. Figure 7.1 illustrates the states and transitions that a stateless session bean instance goes through in its lifetime.
Figure 7-1. Stateless session bean life cycle
When a bean instance is in the Does Not Exist state, it is not an instance in the memory of the system. In other words, it has not been instantiated yet.
Stateless bean instances enter the Method-Ready Pool as the container needs them. When the EJB server is first started, it will probably create a number of stateless bean instances and enter them into the Method-Ready Pool. (The actual behavior of the server depends on the implementation.) When the number of stateless instances servicing client requests is insufficient, more can be created and added to the pool.
When an instance transitions from the Does Not Exist state to the Method-Ready Pool, ...