[[MessageRouter-MessageRouter]]
== Message Router

The
http://www.enterpriseintegrationpatterns.com/MessageRouter.html[Message
Router] from the link:enterprise-integration-patterns.html[EIP patterns]
allows you to consume from an input destination, evaluate some predicate
then choose the right output destination.

image:http://www.enterpriseintegrationpatterns.com/img/MessageRouter.gif[image]

The following example shows how to route a request from an input
*queue:a* endpoint to either *queue:b*, *queue:c* or *queue:d* depending
on the evaluation of various link:predicate.html[Predicate] expressions

=== Examples

The following example shows how to route a request from an input
*seda:a* endpoint to either *seda:b*, *seda:c* or *seda:d* depending on
the evaluation of various link:predicate.html[Predicate] expressions

[source,java]
----
RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("direct:a")
            .choice()
                .when(simple("${header.foo} == 'bar'"))
                    .to("direct:b")
                .when(simple("${header.foo} == 'cheese'"))
                    .to("direct:c")
                .otherwise()
                    .to("direct:d");
    }
};
----

TIP: See link:why-can-i-not-use-when-or-otherwise-in-a-java-camel-route.html[Why
can I not use when or otherwise in a Java Camel route] if you have
problems with the Java DSL, accepting using `when` or `otherwise`.

And the same example using XML:

[source,xml]
----
<camelContext xmlns="http://camel.apache.org/schema/spring">
    <route>
        <from uri="direct:a"/>
        <choice>
            <when>
                <simple>${header.foo} == 'bar'</simple>
                <to uri="direct:b"/>
            </when>
            <when>
                <simple>${header.foo} == 'cheese'</simple>
                <to uri="direct:c"/>
            </when>
            <otherwise>
                <to uri="direct:d"/>
            </otherwise>
        </choice>
    </route>
</camelContext>
----

[[MessageRouter-Choicewithoutotherwise]]
=== Choice without otherwise

If you use a `choice` without adding an `otherwise`, any unmatched
exchanges will be dropped by default.

