Dynamic Router

http://camel.apache.org/dynamic-router.html

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 dynamicRouting Slip which evaluates the slip on-the-fly.

Beware
You must ensure the expression used for the dynamicRouter such as a bean, will returnnull to indicate the end. Otherwise the dynamicRouter will keep repeating endlessly.

Options

NameDefault ValueDescriptionuriDelimiter,Delimiter used if the Expression returned multiple endpoints.ignoreInvalidEndpointsfalseIf an endpoint uri could not be resolved, should it be ignored. Otherwise Camel will thrown an exception stating the endpoint uri is not valid.

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 theDynamic Router implementation is based on top of Routing Slip).

Java DSL

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

from("direct:start")    // use a bean as the dynamic router    .dynamicRouter(method(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";    }    // 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 theExchange, to ensure thread safety, as shown below:

/** * 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 theExchange 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:

<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>        <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. Theroute method would then be invoked repeatedly as the message is processed dynamically. The idea is to return the next endpoint uri where to go. Returnnull to indicate the end. You can return multiple endpoints if you like, just as theRouting 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) {        // 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.

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

• POJO Producing
• Spring Remoting
• Bean component

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.

 

 

 

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http://camel.465427.n5.nabble.com/Exchange-headers-properties-and-dynamic-routers-td3406684.html

Exchange headers/properties and dynamic routers