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Understanding Interceptor Key Concepts

It is imperative that we understand the key concepts of interceptors before we proceed with writing one. Interceptors in Fuji are, in theory, based on the Aspect Oriented Programming(AOP) technique. They allow you to apply advice at a set of point cuts. The following key elements define interceptors in Fuji :

Intercepted Entity

What is Intercepted?

Interceptors are injected onto the message path and can intercept the Messages being exchanged on that path or the entire Message Exchange. So, interceptors can intercept the :

  1. Entire Message Exchange
  2. Message
  3. Message payload

Let's go over each of these in detail.

Intercepting the Message Exchange
This gives the interceptor the most flexibility in altering the course of the message flow and it's content. An interceptor which intercepts a message exchange can

  • read the message(s) in the exchange
  • read the message(s) properties
  • update the message
  • update the message properties
  • update the message exchange status
  • short the exchange

The updates need to be made within the limits of the Message Exchange Pattern Add MEP Link

The message exchange interceptor can short the message exchange, for example a interceptor intercepting the message exchange on the "in" message path, can set the "out" message on the exchange and short it ( we will see in the examples section how a exchange is "shorted"). When the message exchange is shorted this way, the message exchange is marked as "DONE" and sent back to the sender.

Intercepting the Message
Either the "in" or "out" message in the exchange can be intercepted. An interceptor that intercepts a message can

  • read the current message
  • read the current message properties
  • update the current message
  • update the current message properties

Intercepting the Message Payload
Either the "in" or "out" message in the exchange can be intercepted. An interceptor that intercepts a message can

  • read the current message
  • update the current message

"current message" refers to the message being exchanged on the message path when the interceptor is invoked.

Interception Point

Interception Scope

Interceptor

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This particular version was published on 15-Sep-08 15:05 PM, -0700 by JBIWIKI