[[DynamicRouter-DynamicRouter]]
== Dynamic Router

The
http://www.enterpriseintegrationpatterns.com/DynamicRouter.html[Dynamic
Router] from the EIP patterns
allows you to route messages while avoiding the dependency of the router
on all possible destinations while maintaining its efficiency.

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

In *Camel 2.5* we introduced a `dynamicRouter` in the DSL which is like
a dynamic Routing Slip which evaluates the slip
_on-the-fly_.

WARNING: *Beware*
You must ensure the expression used for the `dynamicRouter` such as a
bean, will return `null` to indicate the end. Otherwise the
`dynamicRouter` will keep repeating endlessly.

[[DynamicRouter-Options]]
=== Options

[width="100%",cols="10%,10%,80%",options="header",]
|=======================================================================
|Name |Default Value |Description

|`uriDelimiter` |`,` |Delimiter used if the Expression returned multiple
endpoints.

|`ignoreInvalidEndpoints` |`false` |If an endpoint uri could not be resolved, should it be ignored.
Otherwise Camel will thrown an exception stating the endpoint uri is not
valid.

|`cacheSize` |`1000` |*Camel 2.13.1/2.12.4:* Allows to configure the cache size for the
`ProducerCache` which caches producers for reuse in the routing slip.
Will by default use the default cache size which is 1000. Setting the
value to -1 allows to turn off the cache all together.
|=======================================================================

[[DynamicRouter-DynamicRouterinCamel2.5onwards]]
=== Dynamic Router in Camel 2.5 onwards

From Camel 2.5 the Dynamic Router will set a
property (Exchange.SLIP_ENDPOINT) on the Exchange
which contains the current endpoint as it advanced though the slip. This
allows you to know how far we have processed in the slip. (It's a slip
because the Dynamic Router implementation is
based on top of Routing Slip).

[[DynamicRouter-JavaDSL]]
=== Java DSL

In Java DSL you can use the `dynamicRouter` as shown below:

[source,java]
----
from("direct:start")
    // use a bean as the dynamic router
    .dynamicRouter(method(DynamicRouterTest.class, "slip"));
----

Which will leverage a <<bean-component,Bean>> to compute the slip
_on-the-fly_, which could be implemented as follows:

[source,java]
----
/**
 * Use this method to compute dynamic where we should route next.
 *
 * @param body the message body
 * @return endpoints to go, or <tt>null</tt> to indicate the end
 */
public String slip(String body) {
    bodies.add(body);
    invoked++;
 
    if (invoked == 1) {
        return "mock:a";
    } else if (invoked == 2) {
        return "mock:b,mock:c";
    } else if (invoked == 3) {
        return "direct:foo";
    } else if (invoked == 4) {
        return "mock:result";
    }
 
    // no more so return null
    return null;
}
----

Mind that this example is only for show and tell. The current
implementation is not thread safe. You would have to store the state on
the Exchange, to ensure thread safety, as shown
below:

[source,java]
----
/**
 * Use this method to compute dynamic where we should route next.
 *
 * @param body the message body
 * @param properties the exchange properties where we can store state between invocations
 * @return endpoints to go, or <tt>null</tt> to indicate the end
 */
public String slip(String body, @Properties Map<String, Object> properties) {
    bodies.add(body);
 
    // get the state from the exchange properties and keep track how many times
    // we have been invoked
    int invoked = 0;
    Object current = properties.get("invoked");
    if (current != null) {
        invoked = Integer.valueOf(current.toString());
    }
    invoked++;
    // and store the state back on the properties
    properties.put("invoked", invoked);
 
    if (invoked == 1) {
        return "mock:a";
    } else if (invoked == 2) {
        return "mock:b,mock:c";
    } else if (invoked == 3) {
        return "direct:foo";
    } else if (invoked == 4) {
        return "mock:result";
    }
 
    // no more so return null
    return null;
}
----

You could also store state as message headers, but they are not
guaranteed to be preserved during routing, where as properties on the
Exchange are. Although there was a bug in the method
call expression, see the warning below.

WARNING:*Using beans to store state*
Mind that in Camel 2.9.2 or older, when using a <<bean-component,Bean>> the
state is not propagated, so you will have to use a
Processor instead. This is fixed in Camel 2.9.3
onwards.

[[DynamicRouter-SpringXML]]
=== Spring XML

The same example in Spring XML would be:

[source,xml]
----
<bean id="mySlip" class="org.apache.camel.processor.DynamicRouterTest"/>
 
<camelContext xmlns="http://camel.apache.org/schema/spring">
    <route>
        <from uri="direct:start"/>
        <dynamicRouter>
            <!-- use a method call on a bean as dynamic router -->
            <method ref="mySlip" method="slip"/>
        </dynamicRouter>
    </route>
 
    <route>
        <from uri="direct:foo"/>
        <transform><constant>Bye World</constant></transform>
    </route>
 
</camelContext>
----

[[DynamicRouter-DynamicRouterannotation]]
=== @DynamicRouter annotation

You can also use the `@DynamicRouter` annotation, for example the Camel
2.4 example below could be written as follows. The `route` method would
then be invoked repeatedly as the message is processed dynamically. The
idea is to return the next endpoint uri where to go. Return `null` to
indicate the end. You can return multiple endpoints if you like, just as
the Routing Slip, where each endpoint is
separated by a delimiter.

[source,java]
----
public class MyDynamicRouter {

    @Consume(uri = "activemq:foo")
    @DynamicRouter
    public String route(@XPath("/customer/id") String customerId, @Header("Location") String location, Document body) {
        // query a database to find the best match of the endpoint based on the input parameteres
        // return the next endpoint uri, where to go. Return null to indicate the end.
    }
}
----

In the above we can use the
Parameter Binding Annotations
to bind different parts of the Message to method
parameters or use an Expression such as using
<<xpath-language,XPath>> or <<xpath-language,XQuery>>.

The method can be invoked in a number of ways as described in the
Bean Integration such as

* POJO Producing
* Spring Remoting
* <<bean-component,Bean>> component

