Core J2EE™ Patterns: Best Practices and Design Strategies

Service Activator

Context

Enterprise beans and other business services need a way to be activated asynchronously.

Problem

When a client needs to access an enterprise bean, it first looks up the bean's home object. The client requests the EJB home to provide a remote reference to the required enterprise bean. The client then invokes business method calls on the remote reference to access the enterprise bean services. All these method calls, such as lookup and remote method calls, are synchronous. The client has to wait until these methods return.

Another factor to consider is the life cycle of an enterprise bean. The EJB specification permits the container to passivate an enterprise bean to secondary storage. As a result, the EJB container has ...