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 4 options, which are listed below.

Name Default Java Type Description

configurationRef (advanced)

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.

source (common)

String

Source to use, instead of message body. You can prefix with variable:, header:, or property: to specify kind of source. Otherwise, the source is assumed to be a variable. Use empty or null to use default source, which is the message body.

resultType (common)

String

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

trim (advanced)

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

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 their own key name, for instance, if there is an IN header with the key name foo then it is 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 resultType="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 second 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, e.g.:

/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 it is different, as you set up 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 the 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 Apache 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

Dependencies

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

If you use Maven you could add the following to your pom.xml, substituting the version number for the latest & greatest release.

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

Spring Boot Auto-Configuration

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

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

The component supports 12 options, which are listed below.

Name Description Default Type

camel.component.xquery.autowired-enabled

Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.

true

Boolean

camel.component.xquery.bridge-error-handler

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

Boolean

camel.component.xquery.configuration

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

Configuration

camel.component.xquery.configuration-properties

To set custom Saxon configuration properties.

Map

camel.component.xquery.enabled

Whether to enable auto configuration of the xquery component. This is enabled by default.

Boolean

camel.component.xquery.lazy-start-producer

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

Boolean

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

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

ModuleURIResolver

camel.language.xquery.configuration-ref

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.

String

camel.language.xquery.enabled

Whether to enable auto configuration of the xquery language. This is enabled by default.

Boolean

camel.language.xquery.namespace

Injects the XML Namespaces of prefix - uri mappings.

List

camel.language.xquery.source

Source to use, instead of message body. You can prefix with variable:, header:, or property: to specify kind of source. Otherwise, the source is assumed to be a variable. Use empty or null to use default source, which is the message body.

String

camel.language.xquery.trim

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

true

Boolean
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