Enterprise JavaBeans, Fourth Edition

The Bean-Container Contract

The environment that surrounds the beans on the EJB server is often called the container. The container is more a concept than a physical construct. It acts as an intermediary between the bean and the EJB server. It manages the EJB objects and EJB homes and helps these constructs to manage bean resources and provide services such as transactions, security, concurrency, and naming at runtime. The distinction between the container and the server is not clearly defined, but the EJB specification defines the component model in terms of the container’s responsibilities, so we will follow that convention here.

Enterprise bean components interact with the EJB container through a well-defined component model. The EntityBean, SessionBean , and MessageDrivenBean interfaces provide callback methods that notify the bean class of life-cycle events. At runtime, the container invokes these methods on the bean instance when relevant events occur. For example, when the container is about to write an entity bean instance’s state to the database, it first calls the bean instance’s ejbStore( ) method. This call gives the bean instance an opportunity to do cleanup on its state before it’s written to the database. The ejbLoad( ) method is called just after the bean’s fields are populated from the database, providing the bean developer with an opportunity to manage the bean’s state before the first business method is called.^[9] Other callback methods can be ...