XQuery Component

Table of Contents

Options
Examples
Variables
Using XML configuration
Using XQuery as transformation
Using XQuery as an endpoint
Examples
Learning XQuery
Loading script from external resource
Dependencies

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.

Options

The XQuery component supports 1 options which are listed below.

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Name	Java Type	Description
moduleURIResolver	`ModuleURIResolver`	To use the custom ModuleURIResolver

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The XQuery component supports 31 endpoint options which are listed below:

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Name	Group	Default	Java Type	Description
resourceUri	common		`String`	Required The name of the template to load from classpath or file system
allowStAX	common	`false`	`boolean`	Whether to allow using StAX mode
configuration	common		`Configuration`	To use a custom Saxon configuration
headerName	common		`String`	To use a Camel Message header as the input source instead of Message body.
moduleURIResolver	common		`ModuleURIResolver`	To use the custom ModuleURIResolver
namespacePrefixes	common		`Map`	Allows to control which namespace prefixes to use for a set of namespace mappings
parameters	common		`Map`	Additional parameters
properties	common		`Properties`	Properties to configure the serialization parameters
resultsFormat	common	`DOM`	`ResultFormat`	What output result to use
resultType	common		`Class<?>`	What output result to use defined as a class
staticQueryContext	common		`StaticQueryContext`	To use a custom Saxon StaticQueryContext
stripsAllWhiteSpace	common	`true`	`boolean`	Whether to strip all whitespaces
bridgeErrorHandler	consumer	`false`	`boolean`	Allows for bridging the consumer to the Camel routing Error Handler which mean any exceptions occurred while the consumer is trying to pickup incoming messages or the likes will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions that will be logged at WARN/ERROR level and ignored.
sendEmptyMessageWhenIdle	consumer	`false`	`boolean`	If the polling consumer did not poll any files you can enable this option to send an empty message (no body) instead.
exceptionHandler	consumer (advanced)		`ExceptionHandler`	To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this options is not in use. By default the consumer will deal with exceptions that will be logged at WARN/ERROR level and ignored.
exchangePattern	consumer (advanced)		`ExchangePattern`	Sets the exchange pattern when the consumer creates an exchange.
pollStrategy	consumer (advanced)		`PollingConsumerPollStrategy`	A pluggable org.apache.camel.PollingConsumerPollingStrategy allowing you to provide your custom implementation to control error handling usually occurred during the poll operation before an Exchange have been created and being routed in Camel.
synchronous	advanced	`false`	`boolean`	Sets whether synchronous processing should be strictly used or Camel is allowed to use asynchronous processing (if supported).
backoffErrorThreshold	scheduler		`int`	The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in.
backoffIdleThreshold	scheduler		`int`	The number of subsequent idle polls that should happen before the backoffMultipler should kick-in.
backoffMultiplier	scheduler		`int`	To let the scheduled polling consumer backoff if there has been a number of subsequent idles/errors in a row. The multiplier is then the number of polls that will be skipped before the next actual attempt is happening again. When this option is in use then backoffIdleThreshold and/or backoffErrorThreshold must also be configured.
delay	scheduler	`500`	`long`	Milliseconds before the next poll. You can also specify time values using units such as 60s (60 seconds) 5m30s (5 minutes and 30 seconds) and 1h (1 hour).
greedy	scheduler	`false`	`boolean`	If greedy is enabled then the ScheduledPollConsumer will run immediately again if the previous run polled 1 or more messages.
initialDelay	scheduler	`1000`	`long`	Milliseconds before the first poll starts. You can also specify time values using units such as 60s (60 seconds) 5m30s (5 minutes and 30 seconds) and 1h (1 hour).
runLoggingLevel	scheduler	`TRACE`	`LoggingLevel`	The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that.
scheduledExecutorService	scheduler		`ScheduledExecutorService`	Allows for configuring a custom/shared thread pool to use for the consumer. By default each consumer has its own single threaded thread pool.
scheduler	scheduler	`none`	`ScheduledPollConsumerScheduler`	To use a cron scheduler from either camel-spring or camel-quartz2 component
schedulerProperties	scheduler		`Map`	To configure additional properties when using a custom scheduler or any of the Quartz2 Spring based scheduler.
startScheduler	scheduler	`true`	`boolean`	Whether the scheduler should be auto started.
timeUnit	scheduler	`MILLISECONDS`	`TimeUnit`	Time unit for initialDelay and delay options.
useFixedDelay	scheduler	`true`	`boolean`	Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details.

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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

Mike Kay’s XQuery Primer
the W3Schools XQuery Tutorial

You might also find the XQuery function reference useful

Loading script from external resource

Available as of 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>