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4.5. Message Router
Overview
A message router, shown in Figure 4.7, “Message Router Pattern”, is a type of filter that consumes messages from a single consumer endpoint and redirects them to the appropriate target endpoint, based on a particular decision criterion. A message router is concerned only with redirecting messages; it does not modify the message content.
Figure 4.7. Message Router Pattern
A message router can easily be implemented in Apache Camel using the
choice() processor, where each of the alternative target endpoints can be selected using a when() subclause (for details of the choice processor, see Section 1.5, “Processors”).
Java DSL example
The following Java DSL example shows how to route messages to three alternative destinations (either
seda:a, seda:b, or seda:c) depending on the contents of the foo header:
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>Choice without otherwise
If you use
choice() without an otherwise() clause, any unmatched exchanges are dropped by default.
