THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Camel supports XPath to allow an Expression or Predicate to be used in the DSL or Xml Configuration. For example you could use XPath to create an Predicate in a Message Filter or as an Expression for a Recipient List.
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If the message body is stream based, which means the input is received by Camel as a stream, then you will only be able to read the content of the stream once. Oftentimes when using XPath as Message Filter or Content Based Router the data will be accessed multiple times. Therefore use Stream caching or convert the message body to a String beforehand. This makes it safe to be re-read multiple times.
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Namespaces
You can easily use namespaces with XPath expressions using the Namespaces helper class.Wiki Markup
Variables
Variables in XPath is defined in different namespaces. The default namespace is http://camel.apache.org/schema/spring.
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Function | Argument | Type | Description |
|---|---|---|---|
| none |
| Will return the |
| the header name | Object | Will return the |
| none |
| Will return the |
| the header name |
| Will return the |
| key for property |
| Camel 2.5: To lookup a property using the Properties component (property placeholders). |
| simple expression | Object | Camel 2.5: To evaluate a Simple expression. |
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Here's an example showing some of these functions in use.Wiki Markup Wiki Markup
Using XML Configuration
If you prefer to configure your routes in your Spring XML file then you can use XPath expressions as follows
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Notice how we can reuse the namespace prefixes, foo in this case, in the XPath expression for easier namespace based XPath expressions! See also this discussion on the mailinglist about using your own namespaces with XPath.
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The XPath expression will return a result type using native XML objects such as org.w3c.dom.NodeList. But many times you want a result type to be a String. To do this you have to instruct the XPath which result type to use.
In Java DSL:
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In Spring DSL you use the resultType attribute to provide a fully qualified classname:
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In @XPath:
Available as of Camel 2.1
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Where we use the XPath function concat to prefix the order name with foo-. In this case we have to specify that we want a String as result type so the concat function works.
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Some users may have XML stored in a header. To apply an XPath statement to a header's value you can do this by defining the headerName attribute.
In XML DSL:Wiki Markup headerName as the 2nd parameter as shown:
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Examples
Here is a simple example using an XPath expression as a predicate in a Message FilterWiki Markup NamespaceBuilder as shown in this exampleWiki Markup choice construct. The first choice evaulates if the message has a header key type that has the value Camel. The 2nd choice evaluates if the message body has a name tag <name> which values is Kong.
If neither is true the message is routed in the otherwise block:Wiki Markup Wiki Markup
XPath Injection
You can use Bean Integration to invoke a method on a bean and use various languages such as XPath to extract a value from the message and bind it to a method parameter.
The default XPath annotation has SOAP and XML namespaces available. If you want to use your own namespace URIs in an XPath expression you can use your own copy of the XPath annotation to create whatever namespace prefixes you want to use.Wiki Markup
Example:
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Using XPathBuilder Without an Exchange
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For example you can do something like this:
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This will match the given predicate.
You can also evaluate for example as shown in the following three examples:
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Evaluating with a String result is a common requirement and thus you can do it a bit simpler:
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Using Saxon with XPathBuilder
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You need to add camel-saxon as dependency to your project. It's now easier to use Saxon with the XPathBuilder which can be done in several ways as shown below. Where as the latter ones are the easiest ones.
Using a factoryWiki Markup
unmigrated-inline-wiki-markupWiki Markup
Setting a Custom XPathFactory Using System Property
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This unit test shows how this can be done to use Saxon instead:Wiki Markup INFO level if it uses a non default XPathFactory such as:
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To use Apache Xerces you can configure the system property:
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Enabling Saxon from Spring DSL
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Similarly to Java DSL, to enable Saxon from Spring DSL you have three options:
Specifying the factory
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Specifying the object model
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Shortcut
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Namespace Auditing to Aid Debugging
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Every time a new XPath expression is created in the internal pool, Camel will log the namespace context of the expression under the org.apache.camel.builder.xml.XPathBuilder logger. Since Camel represents Namespace Contexts in a hierarchical fashion (parent-child relationships), the entire tree is output in a recursive manner with the following format:
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Any of these options can be used to activate this logging:
- Enable
TRACElogging on theorg.apache.camel.builder.xml.XPathBuilderlogger, or some parent logger such asorg.apache.camelor the root logger. - Enable the
logNamespacesoption as indicated in Auditing Namespaces, in which case the logging will occur on theINFOlevel.
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AuditingNamespaces
Auditing namespaces
Camel is able to discover and dump all namespaces present on every incoming message before evaluating an XPath expression, providing all the richness of information you need to help you analyse and pinpoint possible namespace issues. To achieve this, it in turn internally uses another specially tailored XPath expression to extract all namespace mappings that appear in the message, displaying the prefix and the full namespace URI(s) for each individual mapping.
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You can enable this option in Java DSL and Spring DSL.
Java DSL:
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Spring DSL:
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The result of the auditing will be appear at the INFO level under the org.apache.camel.builder.xml.XPathBuilder logger and will look like the following:
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Loading Script from External Resource
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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:
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Dependencies
The XPath language is part of camel-core.