[CONF] Apache Camel: XPath (page edited)

Tue, 22 Jul 2008 22:33:03 -0700

Page Edited : CAMEL : XPath

XPath has been edited by Claus Ibsen (Jul 22, 2008).

Change summary:

fixed the wrong sample for xpath and added a new sample for the $header syntax

(View changes)

Content:

XPath

Camel supports XPath to allow an _expression_ or Predicate to be used in the DSL or Xml Configuration. For example you could use XPath to create an Predicate in a Message Filter or as an _expression_ for a Recipient List.

From 1.3 of Camel onwards you can use XPath expressions directly using smart completion in your IDE as follows:

from("queue:foo").
  filter().xpath("//foo")).
  to("queue:bar")




from("queue:foo").
  choice().xpath("//foo")).to("queue:bar").
  otherwise().to("queue:others");





Notice: The xpath is outside the filter node; after the ( ) braces.



In earlier versions of Camel you had to use the XPathBuilder methods then you can use the xpath() function inside your rules. 





import static org.apache.camel.builder.xpath.XPathBuilder.*;
...
from("queue:foo").filter(xpath("//foo")).to("queue:bar")







import static org.apache.camel.builder.xpath.XPathBuilder.*;
...
from("queue:foo").choice(xpath("//foo")).to("queue:bar").
otherwise().to("queue:others");




Notice: The xpath is inside the filter node; within the ( ) braces.



Namespaces



In 1.3 onwards you can easily use namespaces with XPath expressions using the Namespaces helper class.





Namespaces ns = new Namespaces("c", "http://acme.com/cheese");

from("direct:start").filter().
    xpath("/c:[EMAIL PROTECTED]'James']", ns).
    to("mock:result");





Using XML configuration



If you prefer to configure your routes in your Spring XML file then you can use XPath expressions as follows





<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:foo="http://example.com/person"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
       http://activemq.apache.org/camel/schema/spring http://activemq.apache.org/camel/schema/spring/camel-spring.xsd">

  <camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
    <route>
      <from uri="activemq:MyQueue"/>
      <filter>
        <xpath>/foo:[EMAIL PROTECTED]'James']</xpath>
        <to uri="mqseries:SomeOtherQueue"/>
      </filter>
    </route>
  </camelContext>
</beans>





Notice how we can reuse the namespace prefixes, foo in this case, in the XPath _expression_ for easier namespace based XPath expressions!



Examples



Here is a simple example using an XPath _expression_ as a predicate in a Message Filter





from("direct:start").
        filter().xpath("/[EMAIL PROTECTED]'James']").
        to("mock:result");





If you have a standard set of namespaces you wish to work with and wish to share them across many different XPath expressions you can use the NamespaceBuilder as shown in this example





// lets define the namespaces we'll need in our filters
Namespaces ns = new Namespaces("c", "http://acme.com/cheese")
        .add("xsd", "http://www.w3.org/2001/XMLSchema");

// now lets create an xpath based Message Filter
from("direct:start").
        filter(ns.xpath("/c:[EMAIL PROTECTED]'James']")).
        to("mock:result");





In this sample we have a choice construct. The first choice evaulates if the message has a header key type that has the value Camel.

The 2nd choice evaluates if the message body has a name tag <name> which values is Kong.

If neither is true the message is routed in the otherwise block:




from("direct:in").choice()
    // using $headerName is special notation in Camel to get the header key
    .when().xpath("$type = 'Camel'")
        .to("mock:camel")
    // here we test for the body name tag
    .when().xpath("//name = 'Kong'")
        .to("mock:donkey")
    .otherwise()
        .to("mock:other")
    .end();





XPath injection 



You can use Bean Integration to invoke a method on a bean and use various languages such as XPath to extract a value from the message and bind it to a method parameter.



The default XPath annotation has SOAP and XML namespaces available. If you want to use your own namespace URIs in an XPath _expression_ you can use your own copy of the XPath annotation to create whatever namespace prefixes you want to use. 



i.e. cut and paste the XPath annotation code to your own project in a different package and/or annotation name then add whatever namespace prefix/uris you want in scope when you use your annotation on a method parameter. Then when you use your annotation on a method parameter all the namespaces you want will be available for use in your XPath _expression_.



For example





public class Foo {
	
    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(@Path("/foo/bar/text()") String correlationID, @Body String body) {
		// process the inbound message here
    }
}

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