Chapter 8. Message Routing

Abstract

The message routing patterns describe various ways of linking message channels together. This includes various algorithms that can be applied to the message stream (without modifying the body of the message).

8.1. Content-Based Router

Overview

A content-based router, shown in Figure 8.1, “Content-Based Router Pattern”, enables you to route messages to the appropriate destination based on the message contents.

Figure 8.1. Content-Based Router Pattern

Content-based router pattern

Java DSL example

The following example shows how to route a request from an input, seda:a, endpoint to either seda:b, queue:c, or seda:d depending on the evaluation of various predicate expressions: 
RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").choice()
          .when(header("foo").isEqualTo("bar")).to("seda:b")
          .when(header("foo").isEqualTo("cheese")).to("seda:c")
          .otherwise().to("seda:d");
    }
};

XML configuration example

The following example shows how to configure the same route in XML: 
<camelContext id="buildSimpleRouteWithChoice" xmlns="http://camel.apache.org/schema/spring">
  <route>
    <from uri="seda:a"/>
    <choice>
      <when>
        <xpath>$foo = 'bar'</xpath>
        <to uri="seda:b"/>
      </when>
      <when>
        <xpath>$foo = 'cheese'</xpath>
        <to uri="seda:c"/>
      </when>
      <otherwise>
        <to uri="seda:d"/>
      </otherwise>
    </choice>
  </route>
</camelContext>