Apache Camel: Dynamic Router

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.

Options

confluenceTableSmall

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.

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 dynamicRouter as shown below:

{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/DynamicRouterTest.java}

Which will leverage a Bean to compute the slip on-the-fly, which could be implemented as follows:

{snippet:id=e2|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/DynamicRouterTest.java}

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:

{snippet:id=e2|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/DynamicRouterExchangePropertiesTest.java}

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.

Using beans to store state

Mind that in Camel 2.9.2 or older, when using a Bean the state is not propagated, so you will have to use a Processor instead. This is fixed in Camel 2.9.3 onwards.

Spring XML

The same example in Spring XML would be:

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringDynamicRouterTest.xml}

@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.

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. } }

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.

java

public class MyDynamicRouter { @Consume(uri = "activemq:foo") @RecipientList public List<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 ... } }

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

Dynamic Router

Options

Dynamic Router in Camel 2.5 onwards

Java DSL

Spring XML

@DynamicRouter annotation

Dynamic Router in Camel 2.4 or older

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