XQuery

Since Camel 1.0

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

XQuery Language options

The XQuery language supports 3 options, which are listed below.

Name Default Java Type Description

type

String

Sets the class name of the result type (type from output) The default result type is NodeSet

headerName

String

Name of header to use as input, instead of the message body

trim

true

Boolean

Whether to trim the value to remove leading and trailing whitespaces and line breaks

Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-saxon-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 8 options, which are listed below.

Name Description Default Type

camel.component.xquery.configuration

To use a custom Saxon configuration. The option is a net.sf.saxon.Configuration type.

String

camel.component.xquery.configuration-properties

To set custom Saxon configuration properties

Map

camel.component.xquery.enabled

Enable xquery component

true

Boolean

camel.component.xquery.module-u-r-i-resolver

To use the custom ModuleURIResolver. The option is a net.sf.saxon.lib.ModuleURIResolver type.

String

camel.component.xquery.resolve-property-placeholders

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

Boolean

camel.language.xquery.enabled

Enable xquery language

true

Boolean

camel.language.xquery.trim

Whether to trim the value to remove leading and trailing whitespaces and line breaks

true

Boolean

camel.language.xquery.type

Sets the class name of the result type (type from output) The default result type is NodeSet

String

Examples

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

in.body

Object

The In message’s body

out.body

Object

The OUT message’s body (if any)

in.headers.*

Object

You can access the value of exchange.in.headers with key foo by using the variable which name is in.headers.foo

out.headers.*

Object

You can access the value of exchange.out.headers with key foo by using the variable which name is out.headers.foo variable

key name

Object

Any exchange.properties and exchange.in.headers and any additional parameters set using setParameters(Map). These parameters is added with they own key name, for instance if there is an IN header with the key name foo then its added as foo.

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.xsd
       http://camel.apache.org/schema/spring http://camel.apache.org/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!

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 transformation

We can do a message translation using transform or setBody in the route, as shown below:

from("direct:start").
   transform().xquery("/people/person");

Notice that xquery will use DOMResult by default, so if we want to grab the value of the person node, using text() we need to tell xquery to use String as result type, as shown:

from("direct:start").
   transform().xquery("/people/person/text()", String.class);

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://camel.apache.org/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

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

You might also find the XQuery function reference useful

Loading script from external resource

Since Camel 2.11

You can externalize the script and have Camel load it from a resource such as "classpath:", "file:", or "http:".

 This is done using the following syntax: `"resource:scheme:location"`,
eg to refer to a file on the classpath you can do:
.setHeader("myHeader").xquery("resource:classpath:myxquery.txt", String.class)

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>x.x.x</version>
</dependency>
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