Chapter 33. XQuery

XQuery was originally devised as a query language for data stored in XML form in a database. The XQuery language enables you to select parts of the current message, when the message is in XML format. XQuery is a superset of the XPath language; hence, any valid XPath expression is also a valid XQuery expression.

You can pass an XQuery expression to xquery() in several ways. For simple expressions, you can pass the XQuery expressions as a string (java.lang.String). For longer XQuery expressions, you might prefer to store the expression in a file, which you can then reference by passing a java.io.File argument or a java.net.URL argument to the overloaded xquery() method. The XQuery expression implicitly acts on the message content and returns a node set as the result. Depending on the context, the return value is interpreted either as a predicate (where an empty node set is interpreted as false) or as an expression.

To use XQuery in your routes you need to add a dependency on camel-saxon to your project as shown in Example 33.1, “Adding the camel-saxon dependency”.

<!-- Maven POM File -->
...
<dependencies>
  ...
  <dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-saxon</artifactId>
    <version>${camel-version}</version>
  </dependency>
  ...
</dependencies>

The camel-saxon component is supported by the Camel on EAP (Wildfly Camel) framework, which offers a simplified deployment model on the Red Hat JBoss Enterprise Application Platform (JBoss EAP) container. For details of this model, see chapter "Apache Camel on Red Hat JBoss EAP" in "Deploying into a Web Server".

To use the xquery() static method in your application code, include the following import statement in your Java source files:

import static org.apache.camel.builder.saxon.XQueryBuilder.xquery;

Table 33.1, “XQuery variables” lists the variables that are accessible when using XQuery.

Example 33.2, “Route using XQuery” shows a route that uses XQuery.

<camelContext>
  <route>
    <from uri="activemq:MyQueue"/>
    <filter>
      <language langauge="xquery">/foo:person[@name='James']</language>
      <to uri="mqseries:SomeOtherQueue"/>
    </filter>
  </route>
</camelContext>