Python

Since Camel 1.0

Camel supports Python among other Scripting Languages to allow an Expression or Predicate to be used in the DSL or Xml Configuration.

To use a Python expression use the following Java code

... python("somePythonExpression") ...

For example you could use the python function to create an Predicate in a Message Filter or as an Expression for a Recipient List

Python Language Options

The Python language supports 1 options, which are listed below.

Name Default Java Type Description

trim

true

Boolean

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

Example

In the sample below we use Python to create a Predicate use in the route path, to route exchanges from admin users to a special queue.

    from("direct:start")
        .choice()
            .when().python("request.headers['user'] == 'admin'").to("seda:adminQueue")
        .otherwise()
            .to("seda:regularQueue");

And a Spring DSL sample as well:

    <route>
        <from uri="direct:start"/>
        <choice>
            <when>
                <python>request.headers['user'] == 'admin'</python>
                <to uri="seda:adminQueue"/>
            </when>
            <otherwise>
                <to uri="seda:regularQueue"/>
            </otherwise>
        </choice>
    </route>

ScriptContext

The JSR-223 scripting languages ScriptContext is pre configured with the following attributes all set at ENGINE_SCOPE:

Attribute Type Value

context

org.apache.camel.CamelContext

The Camel Context ( It cannot be used in groovy)

camelContext

org.apache.camel.CamelContext

The Camel Context

exchange

org.apache.camel.Exchange

The current Exchange

request

org.apache.camel.Message

The message (IN message)

response

org.apache.camel.Message

Deprecated: The OUT message. The OUT message if null by default. Use IN message instead.

properties

org.apache.camel.builder.script.PropertiesFunction

Camel 2.9: Function with a resolve method to make it easier to use Camels Properties component from scripts. See further below for example.

See Scripting Languages for the list of languages with explicit DSL support.

Additional arguments to ScriptingEngine

Since Camel 2.8

You can provide additional arguments to the ScriptingEngine using a header on the Camel message with the key CamelScriptArguments.

See this example:

Using properties function

Since Camel 2.9

If you need to use the Properties component from a script to lookup property placeholders, then its a bit cumbersome to do so.

 For example to set a header name myHeader with a value from a property
placeholder, which key is provided in a header named "foo".
.setHeader("myHeader").groovy("context.resolvePropertyPlaceholders('{{' + request.headers.get('foo') + '}}')")

From Camel 2.9 onwards you can now use the properties function and the same example is simpler:

.setHeader("myHeader").groovy("properties.resolve(request.headers.get('foo'))")

Loading script from external resource

Since 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").groovy("resource:classpath:mygroovy.groovy")

How to get the result from multiple statements script

Since Camel 2.14

As the scripteengine evale method just return a Null if it runs a multiple statments script. Camel now look up the value of script result by using the key of "result" from the value set. If you have multiple statements script, you need to make sure you set the value of result variable as the script return value.

bar = "baz";
# some other statements ...
# camel take the result value as the script evaluation result
result = body * 2 + 1

Dependencies

To use scripting languages in your camel routes you need to add the a dependency on camel-script which integrates the JSR-223 scripting engine.

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-script</artifactId>
  <version>x.x.x</version>
</dependency>
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