9.10. Avoid Chaining Stateful Session Beans
In developing session-only systems you will be tempted to use stateful session beans from inside other stateful session beans. While this appears to be a good modeling approach, it's problematic. Chaining stateful session beans can lead to problems when beans time out or throw exceptions that cause them to become invalid. Figure 9-1 shows a chain of stateful session beans, each of which maintains conversational state that other beans depend on to complete an operation encapsulated by bean A.
Figure 9-1. Chain of stateful session beans
If any one of the beans in this chain times out, say bean B, the conversational state trailing that bean is lost. If this conversational state was built up over a long time, considerable work can be lost. The chain of stateful session beans is only as strong as its weakest link. If one bean times out or becomes invalid, the entire conversational state on which bean A depends becomes invalid. Avoid chaining stateful session beans.
Using stateless session beans from within stateful session beans is not a problem, because a stateless session bean does not maintain any conversational state. Use stateless session beans from within stateful session beans as much as you need.
Using a stateful session bean from within a stateless session bean is almost nonsensical because the benefit of the stateful session bean's conversational state cannot be leveraged beyond the scope of the stateless session bean's method.
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