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Figure 2.3 shows an example of a processor pipeline for InOnly exchanges. Processor A acts by modifying the In message, while processors B and C create an Out message. The route builder links the processors together as shown.

In particular, processors B and C are linked together in the form of a pipeline. Processor B's Out message is moved to the In message before feeding the exchange into processor C, and processor C's Out message is moved to the In message before feeding the exchange into the producer endpoint. Thus the processors' outputs and inputs are joined into a continuous pipeline, as shown in Figure 2.3.


Fuse Mediation Router employs the pipeline pattern by default, so you do not need to use any special syntax to create a pipeline in your routes. For example, Example 2.3 pulls messages from a userdataQueue queue, pipes the message through a Velocity template (to produce a customer address in text format), and then sends the resulting text address to the queue, envelopeAddressQueue.


Where the Velocity endpoint, velocity:file:AdressTemplate.vm, specifies the location of a Velocity template file, file:AdressTemplate.vm, in the file system. The setExchangePattern command changes the exchange pattern to InOut before sending the exchange to the Velocity endpoint and then changes it back to InOnly afterwards. For more details of the Velocity endpoint, see Velocity in Component Reference.

Figure 2.4 shows an example of a processor pipeline for InOut exchanges, which you typically use to support remote procedure call (RPC) semantics. Processors A, B, and C are linked together in the form of a pipeline, with the output of each processor being fed into the input of the next. The final Out message produced by the producer endpoint is sent all the way back to the consumer endpoint, where it provides the reply to the original request.


[Note]Note

In order to support the InOut exchange pattern, it is essential that the last node in the route creates an Out message. Otherwise, any client that connects to the consumer endpoint would hang and wait indefinitely for a reply message.

Example 2.4 shows a route that processes payment requests that are received via HTTP.


The incoming payment request is processed by passing it through a pipeline of Web services, cxf:bean:addAccountDetails, cxf:bean:getCreditRating, and cxf:bean:processTransaction. The final Web service, processTransaction, generates a response (Out message) that is sent back through the JETTY endpoint.

When the pipeline consists of just a sequence of endpoints, it is also possible to use the alternative syntax shown in Example 2.5.


The pipeline for InOptionalOut exchanges is essentially the same as the pipeline in Figure 2.4. The difference between InOut and InOptionalOut is that an exchange with the InOptionalOut exchange pattern is allowed to have a null Out message as a reply. That is, in the case of an InOptionalOut exchange, a null Out message is copied to the In message of the next node in the pipeline. By contrast, in the case of an InOut exchange, a null Out message is discarded and the original In message from the current node would be copied to the In message of the next node instead.

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