Using Session Beans

This section provides guidelines for creating session beans in the Application Server environment. This section addresses the following topics:

• About the Session Bean Containers

• Restrictions and Optimizations

Extensive information on session beans is contained in the chapters 6, 7, and 8 of the Enterprise JavaBeans Specification, v2.1.

About the Session Bean Containers

Like an entity bean, a session bean can access a database through Java^TM Database Connectivity (JDBC^TM) calls. A session bean can also provide transaction settings. These transaction settings and JDBC calls are referenced by the session bean’s container, allowing it to participate in transactions managed by the container.

A container managing stateless session beans has a different charter from a container managing stateful session beans.

Stateless Container

The stateless container manages stateless session beans, which, by definition, do not carry client-specific states. All session beans (of a particular type) are considered equal.

A stateless session bean container uses a bean pool to service requests. The Application Server specific deployment descriptor file, sun-ejb-jar.xml, contains the properties that define the pool:

• steady-pool-size

• resize-quantity

• max-pool-size

• pool-idle-timeout-in-seconds

For more information about sun-ejb-jar.xml, see The sun-ejb-jar.xml File.

The Application Server provides the wscompile and wsdeploy tools to help you implement a web service endpoint as a stateless session bean. For more information about these tools, see the Sun Java System Application Server Platform Edition 8.1 2005Q2 Update 2 Reference Manual.

Stateful Container

The stateful container manages the stateful session beans, which, by definition, carry the client-specific state. There is a one-to-one relationship between the client and the stateful session beans. At creation, each stateful session bean (SFSB) is given a unique session ID that is used to access the session bean so that an instance of a stateful session bean is accessed by a single client only.

Stateful session beans are managed using cache. The size and behavior of stateful session beans cache are controlled by specifying the following sun-ejb-jar.xml parameters:

• max-cache-size

• resize-quantity

• cache-idle-timeout-in-seconds

• removal-timeout-in-seconds

• victim-selection-policy

The max-cache-size element specifies the maximum number of session beans that are held in cache. If the cache overflows (when the number of beans exceeds max-cache-size), the container then passivates some beans or writes out the serialized state of the bean into a file. The directory in which the file is created is obtained from the EJB container using the configuration APIs.

For more information about sun-ejb-jar.xml, see The sun-ejb-jar.xml File.

The passivated beans are stored on the file system. The Session Store Location setting in the EJB container allows the administrator to specify the directory where passivated beans are stored. By default, passivated stateful session beans are stored in application-specific subdirectories created under domain-dir/session-store.

Make sure the delete option is set in the server.policy file, or expired file-based sessions might not be deleted properly. For more information about server.policy, see The server.policy File.

Restrictions and Optimizations

This section discusses restrictions on developing session beans and provides some optimization guidelines:

• Optimizing Session Bean Performance

• Restricting Transactions

Optimizing Session Bean Performance

For stateful session beans, colocating the stateful beans with their clients so that the client and bean are executing in the same process address space improves performance.

Restricting Transactions

The following restrictions on transactions are enforced by the container and must be observed as session beans are developed:

• A session bean can participate in, at most, a single transaction at a time.

• If a session bean is participating in a transaction, a client cannot invoke a method on the bean such that the trans-attribute element in the ejb-jar.xml file would cause the container to execute the method in a different or unspecified transaction context or an exception is thrown.

• If a session bean instance is participating in a transaction, a client cannot invoke the remove method on the session object’s home or component interface object or an exception is thrown.