Sunday, March 17, 2013

Implementing Pipes and Filters Using Camel

Pipes and Filters is an integration pattern that solves the problem of having to process a job or task in a series of sub-tasks. If you're not familiar with pipes and filters, read my post on describing the design: Pipes and Filters - Integration Pattern.

This tutorial describes how to implement the pipes and filters integration pattern using Apache Camel. The source code is on GitHub:

The key component of this application is the Camel route that's defined in spring-context.xml:

<camelContext xmlns="">

  <!-- pipes and filters example -->
 <!-- get message from JMS FOO.BAR queue -->
 <from uri="activemq:queue:FOO.BAR" />

 <!-- use the simple language to transform the input to upper case -->
 <!-- route the input to the messageReceiver bean, which will modify the message slightly -->
 <to uri="bean:messageReceiver?method=processMessage"/>
 <!-- route the output from the messageReceiver bean to the output console -->
 <to uri="stream:out"/>


This route has four steps/filters. The pipeline begins when a JMS message is posted on the FOO.BAR queue. Next, I'm using Camel to convert the message body to upper-case. The third step in the pipeline sends the result of the upper-case transformation to a Spring bean with an ID of "messageReceiver". Notice the use of "?method=processMessage". This allows us to route the message to the processMessage() method on the messageReceiver bean. The last step of the pipeline is to output the results of the processMessage() method to the console.

In summary, the following items are the main components when implementing the pipes and filters integration pattern in Camel:

  1. Defining the Camel route. In this example, I'm using Spring to define the route.
  2. The result of the first step is the input to the second step. The result of the second step is the input to the third step. And so on...
  3. Use the following Camel URI to route a specific message in a Java class, where {beanId} is substituted with the ID of the Spring bean and {methodName} is the name of the method in the bean.

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