[CONF] Apache Camel: Recipient List (page edited)

Mon, 02 Feb 2009 10:25:29 -0800

Page Edited : CAMEL : Recipient List

Recipient List has been edited by Jonathan Anstey (Feb 02, 2009).

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Content:

Recipient List

The Recipient List from the EIP patterns allows you to route messages to a number of dynamically specified recipients.

Static Recipient List

The following example shows how to route a request from an input queue:a endpoint to a static list of destinations

Using Annotations
You can use the RecipientList Annotation on a POJO to create a Dynamic Recipient List. For more details see the Bean Integration.

Using the Fluent Builders

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").multicast().to("seda:b", "seda:c", "seda:d");
    }
};


Using the Spring XML Extensions




<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <multicast>
      <to uri="seda:b"/>
      <to uri="seda:c"/>
      <to uri="seda:d"/>
    </multicast>
  </route>
</camelContext>





Dynamic Recipient List



Usually one of the main reasons for using the Recipient List pattern is that the list of recipients is dynamic and calculated at runtime. The following example demonstrates how to create a dynamic recipient list using an _expression_ (which in this case it extracts a named header value dynamically) to calculate the list of endpoints which are either of type Endpoint or are converted to a String and then resolved using the endpoint URIs.



Using the Fluent Builders




RouteBuilder builder = new RouteBuilder() {
    public void configure() {
        from("seda:a").recipientList(header("foo"));
    }
};





The above assumes that the header contains a list of endpoint URIs. The following takes a single string header and tokenizes it




from("direct:a").recipientList(
        header("recipientListHeader").tokenize(","));





Iteratable value


The dynamic list of recipients that are defined in the header must be iteratable such as:


    
	
  • java.util.Collection
    • 
	
  • java.util.Iterator
    • 
	
  • arrays
    • 
	
  • org.w3c.dom.NodeList
    • 
	
  • Camel 1.5.1: a single String with values separated with comma
    • 
	
  • any other type will be regarded as a single value
    • 





Using the Spring XML Extensions




<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
  <route>
    <from uri="seda:a"/>
    <recipientList>
      <xpath>$foo</xpath>
    </recipientList>
  </route>
</camelContext>





For further examples of this pattern in use you could look at one of the junit test case



Using delimiter in Spring XML


Available as of Camel 1.5.1

In Spring DSL you can set the delimiter attribute for setting a delimiter to be used if the header value is a single String with multiple separated endpoints.





<route>
  <from uri="direct:a" />
  <!-- use comma as a delimiter for String based values -->
  <recipientList delimiter=",">
    <header>myHeader</header>
  </recipientList>
</route>





So if myHeader contains a String with the value "activemq:queue:foo, activemq:topic:hello , log:bar" then Camel will split the String using the delimiter given in the XML that was comma, resulting into 3 endpoints to send to. You can use spaces between the endpoints as Camel will trim the value when it lookup the endpoint to send to. 



Note: In Java DSL you use the tokenizer to archive the same. The route above in Java DSL:




from("direct:a").recipientList(header("myHeader").tokenize(","));





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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