Messaging Technologies

 The J2EE messaging technologies provide standard APIs that WebLogic Server applications can use to communicate with one another as well as with non-WebLogic Server applications. The messaging services include the following APIs:

• Java Message Service (JMS) 
• JavaMail

The following sections describe these APIs in detail.

JMS

      Java Messaging Service (JMS) enables applications to communicate with one another by exchanging messages. A message is a request, report, and/or event that contains the information needed to coordinate communication between different applications. A message provides a level of abstraction, allowing you to separate details about the destination system from the application code.

WebLogic JMS implements two messaging models: point-to-point (PTP) and publish/subscribe (pub/sub). The PTP model allows any number of senders to send messages to a Queue. Each message in the Queue is delivered to a single reader. The pub/sub model allows any number of senders to send messages to a Topic. Each message on the Topic is sent to every reader with a subscription to the Topic. Messages can be delivered to readers synchronously or asynchronously; the particular messaging mode can be controlled either using the Administration Console or via the method used to send messages in the JMS application.

JMS messages can be persistent or non-persistent. Persistent messages are stored in a database and are not lost if WebLogic Server restarts. Non-persistent messages are lost if WebLogic Server is restarted. Persistent messages sent to a Topic can be retained until all interested subscribers have received them.

JMS supports several message types that are useful for different types of applications. The message body can contain arbitrary text, byte streams, Java primitive data types, name/value pairs, serializable Java objects, or XML content.

JavaMail

         WebLogic Server includes the Sun JavaMail reference implementation. JavaMail allows an application to create e-mail messages and send them through an SMTP server on the network.