Dynamic Router
The 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.
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.
| 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. |
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).
Java DSL
In Java DSL you can use the routingSlip as shown below:
from("direct:start")
.dynamicRouter(bean(DynamicRouterTest.class, "slip"));
Which will leverage a Bean to compute the slip on-the-fly, which could be implemented as follows:
/**
* 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";
}
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.
Spring XML
The same example in Spring XML would be:
<bean id="mySlip" class="org.apache.camel.processor.DynamicRouterTest"/>
<camelContext xmlns="http://camel.apache.org/schema/spring">
<route>
<from uri="direct:start"/>
<dynamicRouter>
<method ref="mySlip" method="slip"/>
</dynamicRouter>
</route>
<route>
<from uri="direct:foo"/>
<transform><constant>Bye World</constant></transform>
<to uri="mock:foo"/>
</route>
</camelContext>
@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.
public class MyDynamicRouter {
@Consume(uri = "activemq:foo")
@DynamicRouter
public String route(@XPath("/customer/id") String customerId, @Header("Location") String location, Document body) {
}
}
Dynamic Router in Camel 2.4 or older
The simplest way to implement this is to use the RecipientList Annotation on a Bean method to determine where to route the message.
public class MyDynamicRouter {
@Consume(uri = "activemq:foo")
@RecipientList
public List<String> route(@XPath("/customer/id") String customerId, @Header("Location") String location, Document body) {
...
}
}
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 or XQuery.
The method can be invoked in a number of ways as described in the Bean Integration such as
Using This Pattern
If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.