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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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► Session EJBs<br />

They encapsulate ephemeral (nonpermanent) data associated with a<br />

particular EJB client. Unlike the data in an entity bean, the data in a session<br />

bean is not stored in a permanent data source <strong>and</strong> no harm is caused if this<br />

data is lost. However, a session bean can update data in an underlying<br />

database, usually by accessing an entity bean. A session bean can also<br />

participate in a transaction.<br />

When created, instances of a session bean are identical, though some<br />

session beans can store semipermanent data that make them unique at<br />

certain points in their life cycle. A session bean is always associated with a<br />

single client; attempts to make concurrent calls result in an exception being<br />

thrown.<br />

For example, the task associated with transferring funds between two bank<br />

accounts can be encapsulated in a session bean. Such a transfer session<br />

bean can find two instances of an account entity bean (by using the account<br />

IDs), <strong>and</strong> then subtract a specified amount from one account <strong>and</strong> add the<br />

same amount to the other account.<br />

► Message-driven EJBs<br />

These beans where added in the EJB 2.0 specification. These beans are<br />

similar to a session bean, except they respond to a Java Message Service<br />

(JMS) service, thus allowing asynchronous message processing.<br />

16.4.4 Developing content with <strong>IBM</strong> Web application servers<br />

<strong>IBM</strong> offers numerous powerful solutions for Web application development <strong>and</strong><br />

deployment. For more information about these <strong>and</strong> other <strong>IBM</strong> products, refer to<br />

the following link:<br />

http://www.software.ibm.com/webservers<br />

16.5 RFCs relevant to this chapter<br />

The following RFCs provide detailed information about the connection protocols<br />

<strong>and</strong> architectures presented throughout this chapter:<br />

► RFC 1945 – Hypertext Transfer Protocol -- HTTP/1.0 (May 1996)<br />

► RFC 2616 – Hypertext Transfer Protocol -- HTTP/1.1 (June 1999)<br />

► RFC 2617 – HTTP Authentication (June 1999)<br />

► RFC 2817 – Upgrading to TLS Within HTTP/1.1 (May 2000)<br />

► RFC 2822 – Internet Message Format (April 2001)<br />

► RFC 3986 – Uniform Resource Identifiers (January 2005)<br />

Chapter 16. The Web 621

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