29.2. XML DSL
Basic expressions
To evaluate an XPath expression in the XML DSL, put the XPath expression inside an
xpath element. The XPath expression is applied to the body of the current In message and returns an XML node (or node set). Typically, the returned XML node is automatically converted to a string.
For example, to extract the contents of the
/person/name element from the current In message body and use it to set a header named user, you could define a route like the following:
<beans ...>
<camelContext xmlns="http://camel.apache.org/schema/spring">
<route>
<from uri="queue:foo"/>
<setHeader headerName="user">
<xpath>/person/name/text()</xpath>
</setHeader>
<to uri="direct:tie"/>
</route>
</camelContext>
</beans>
If you want to convert the result to a specific type, specify the result type by setting the
resultType attribute to a Java type name (where you must specify the fully-qualified type name). For example, to specify explicitly that the result type is java.lang.String (you can omit the java.lang. prefix here):
<xpath resultType="String">/person/name/text()</xpath>
Namespaces
When processing documents whose elements belong to one or more XML schemas, it is typically necessary to associate namespace URIs with prefixes, so that you can identify element names unambiguously in your XPath expressions. It is possible to use the standard XML mechanism for associating prefixes with namespace URIs. That is, you can set an attribute like this:
xmlns:Prefix="NamespaceURI".
For example, to associate the prefix,
cust, with the namespace, http://acme.com/customer/record, and then extract the contents of the element, /cust:person/cust:name, you could define a route like the following:
<beans ...>
<camelContext xmlns="http://camel.apache.org/schema/spring"
xmlns:cust="http://acme.com/customer/record" >
<route>
<from uri="queue:foo"/>
<setHeader headerName="user">
<xpath>/cust:person/cust:name/text()</xpath>
</setHeader>
<to uri="direct:tie"/>
</route>
</camelContext>
</beans>Auditing namespaces
One of the most frequent problems that can occur when using XPath expressions is that there is a mismatch between the namespaces appearing in the incoming messages and the namespaces used in the XPath expression. To help you troubleshoot this kind of problem, the XPath language supports an option to dump all of the namespaces from all of the incoming messages into the system log.
To enable namespace logging at the
INFO log level, enable the logNamespaces option in the XML DSL, as follows:
<xpath logNamespaces="true" resultType="String">/foo:person/@id</xpath>
Alternatively, you could configure your logging system to enable
TRACE level logging on the org.apache.camel.builder.xml.XPathBuilder logger.
When namespace logging is enabled, you will see log messages like the following for each processed message:
2012-01-16 13:23:45,878 [stSaxonWithFlag] INFO XPathBuilder -
Namespaces discovered in message: {xmlns:a=[http://apache.org/camel],
DEFAULT=[http://apache.org/default],
xmlns:b=[http://apache.org/camelA, http://apache.org/camelB]}