[CONF] Apache Camel: XQuery (page edited)

Thu, 25 Sep 2008 03:49:36 -0700

Page Edited : CAMEL : XQuery

XQuery has been edited by Claus Ibsen (Sep 25, 2008).

(View changes)

Content:

XQuery

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

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


You can also use functions inside your query, in which case you need an explicit type conversion (or you will get a org.w3c.dom.DOMException: HIERARCHY_REQUEST_ERR) by passing the Class as a second argument to the xquery() method.





from("direct:start").
  recipientList().xquery("concat('mock:foo.', /person/@city)", String.class);





Variables



The IN message body will be set as the contextItem. Besides this these Variables is also added as parameters:






 Variable 
 Type 
 Description 




 exchange 
 Exchange 
 The current Exchange 




 out 
 Message 
 The OUT message (if any) 




 this 
 Object 
 Any exchange.properties and exchange.in.headers and any additional parameters set using setParameters(Map). 






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>
        <xquery>/foo:[EMAIL PROTECTED]'James']</xquery>
        <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 XQuery expressions!



When you use functions in your XQuery _expression_ you need an explicit type conversion which is done in the xml configuration via the @type attribute: 





<xquery type="java.lang.String">concat('mock:foo.', /person/@city)</xquery>





Using XQuery as an endpoint



Sometimes an XQuery _expression_ can be quite large; it can essentally be used for Templating. So you may want to use an XQuery Endpoint so you can route using XQuery templates.



The following example shows how to take a message of an ActiveMQ queue (MyQueue) and transform it using XQuery and send it to MQSeries.





<camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
    <route>
      <from uri="activemq:MyQueue"/>
      <to uri="xquery:com/acme/someTransform.xquery"/>
      <to uri="mqseries:SomeOtherQueue"/>
    </route>
  </camelContext>





Examples



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





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





This example uses XQuery with namespaces as a predicate in a Message Filter





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

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





Learning XQuery



XQuery is a very powerful language for querying, searching, sorting and returning XML. For help learning XQuery try these tutorials






You might also find the XQuery function reference useful



Dependencies



To use XQuery in your camel routes you need to add the a dependency on camel-saxon which implements the XQuery language. 



If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).





<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-saxon</artifactId>
  <version>1.4.0</version>
</dependency>

Powered by Atlassian Confluence (Version: 2.2.9 Build:#527 Sep 07, 2006) - Bug/feature request

Unsubscribe or edit your notifications preferences

Reply via email to