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| <!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" |
| "concept.dtd"> |
| <concept id="sessb" xml:lang="en-us"> |
| <title>Session Beans</title> |
| <shortdesc></shortdesc> |
| <prolog><metadata> |
| <keywords><indexterm>session beans<indexterm>overview</indexterm></indexterm> |
| </keywords> |
| </metadata></prolog> |
| <conbody> |
| <p>A <b>session bean</b> is a type of enterprise bean. It is created by a |
| client and usually exists only for the duration of a single client-server |
| session.</p> |
| <p>Session beans are useful for describing interactions between other beans |
| (taskflow) and for implementing particular tasks. They do not represent data |
| in the database, but they can access data, so we can use session beans to |
| read, update, and insert data in a business process. Session beans access |
| data that spans concepts, is not shared, and is usually read-only. Session |
| beans contain business logic, and entities model persistent data. There are |
| three types of session beans: stateless, stateful and singleton. </p> |
| <ul> |
| <li><b>Stateless session beans</b> <p>A stateless session bean is pooled by |
| the container to handle multiple requests from multiple clients and does not |
| maintain any conversational state.</p> </li> |
| <li> <b>Stateful session beans</b> <p>A stateful session bean acts on behalf |
| of a single client and maintains client-specific session information (called |
| conversational state) across multiple method calls and transactions. It exists |
| for the duration of a single client/server session.</p> </li> |
| <li> <b>Singleton session beans</b> <p>A Singleton session bean is a session |
| bean component that is instantiated once per application. In cases where the container |
| is distributed over many virtual machines, each application will have one bean instance |
| of the Singleton for each JVM.</p> </li> |
| </ul> |
| </conbody> |
| </concept> |
