XQuery

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.

To enable XQuery support you need the camel-saxon library to be on your classpath.

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

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

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

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

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:person[@name='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!

Examples

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

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

Learning XQuery

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

• Mike Kay's XQuery Primer
• the W3Schools XQuery Tutorial

You might also find the XQuery function reference useful