Enterprise JavaBeans, Fourth Edition

Stateless Session Bean Timers

Stateless session bean timers can be used for auditing or batch processing . As an auditing agent, a stateless session timer can monitor the state of the system to ensure that tasks are being completed and that data is consistent. This type of work spans entities and possibly data sources. Such EJBs can also perform batch processing work such as database clean up, transfer of records, etc. Stateless session bean timers can also be deployed as agents that perform some type of intelligent work on behalf of the organization they serve. An agent can be thought of as an extension of an audit: it monitors the system but it also fixes problems automatically.

While entity timers are associated with a specific entity bean and primary key, stateless session bean timers are associated only with a specific type of session bean. When a timer for a stateless session bean goes off, the container selects an instance of that stateless bean type from the instance pool and calls its ejbTimeout( ) method. This makes sense, because all stateless session beans in the instance pool are logically equivalent. Any instance can serve any client, including the container itself.

Stateless session timers are often used to manage taskflow or when the timed event applies to a collection of entities instead of just one. For example, stateless session timers might be used to audit all maintenance records to ensure that they meet state and federal guidelines: at specific intervals, ...