XQuery

Since Camel 1.0

Camel supports XQuery to allow an Expression or Predicate to be used in the DSL.

For example, you could use XQuery to create a predicate in a Message Filter or as an expression for a Recipient List.

XQuery Language options

The XQuery language supports 6 options, which are listed below.

Name Default Java Type Description

Name	Default	Java Type	Description
resultType		`String`	Sets the class of the result type (type from output).
type		`String`	Sets the class name of the result type (type from output) The default result type is NodeSet.
configurationRef		`String`	Reference to a saxon configuration instance in the registry to use for xquery (requires camel-saxon). This may be needed to add custom functions to a saxon configuration, so these custom functions can be used in xquery expressions.
headerName		`String`	Name of header to use as input, instead of the message body It has as higher precedent than the propertyName if both are set.
propertyName		`String`	Name of property to use as input, instead of the message body. It has a lower precedent than the headerName if both are set.
trim	`true`	`Boolean`	Whether to trim the value to remove leading and trailing whitespaces and line breaks.

resultType

String

Sets the class of the result type (type from output).

type

String

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

configurationRef

String

Reference to a saxon configuration instance in the registry to use for xquery (requires camel-saxon). This may be needed to add custom functions to a saxon configuration, so these custom functions can be used in xquery expressions.

headerName

String

Name of header to use as input, instead of the message body It has as higher precedent than the propertyName if both are set.

propertyName

String

Name of property to use as input, instead of the message body. It has a lower precedent than the headerName if both are set.

trim

true

Boolean

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

Variables

The message body will be set as the contextItem. And the following variables are available as well:

Variable Type Description

Variable	Type	Description
exchange	Exchange	The current Exchange
in.body	Object	The message body
out.body	Object	deprecated The OUT message 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	deprecated 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 are added with they own key name, for instance if there is an IN header with the key name foo then its added as foo.

exchange

Exchange

The current Exchange

in.body

Object

The message body

out.body

Object

deprecated The OUT message 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

deprecated 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 are added with they own key name, for instance if there is an IN header with the key name foo then its added as foo.

Example

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 an org.w3c.dom.DOMException: HIERARCHY_REQUEST_ERR). You need to pass in the expected output type of the function. For example the concat function returns a String which is done as shown:

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

And in XML DSL:

<route>
  <from uri="direct:start"/>
  <recipientList>
    <xquery type="java.lang.String">concat('mock:foo.', /person/@city</xquery>
  </recipientList>
</route>

Using namespaces

If you have a standard set of namespaces you wish to work with and wish to share them across many XQuery expressions you can use the org.apache.camel.support.builder.Namespaces when using Java DSL as shown:

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

from("direct:start")
  .filter().xquery("/c:person[@name='James']", ns)
  .to("mock:result");

Notice how the namespaces are provided to xquery with the ns variable that are passed in as the 2nd parameter.

Each namespace is a key=value pair, where the prefix is the key. In the XQuery expression then the namespace is used by its prefix, eg:

/c:person[@name='James']

The namespace builder supports adding multiple namespaces as shown:

Namespaces ns = new Namespaces("c", "http://acme.com/cheese")
                     .add("w", "http://acme.com/wine")
                     .add("b", "http://acme.com/beer");

When using namespaces in XML DSL then its different, as you setup the namespaces in the XML root tag (or one of the camelContext, routes, route tags).

In the XML example below we use Spring XML where the namespace is declared in the root tag beans, in the line with xmlns:foo="http://example.com/person":

<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>

This namespace uses foo as prefix, so the <xquery> expression uses foo: to use this namespace.

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);

If you want to use Camel variables like headers, you have to explicitly declare them in the XQuery expression.

<transform>
    <xquery>
        declare variable $in.headers.foo external;
        element item {$in.headers.foo}
    </xquery>
</transform>

Loading script from external resource

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", e.g. to refer to a file on the classpath you can do:

.setHeader("myHeader").xquery("resource:classpath:myxquery.txt", String.class)

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

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>

Unresolved include directive in modules/languages/pages/xquery-language.adoc - include::spring-boot:partial$starter.adoc[]