Camel Components

Python

Since Camel 3.19

Camel allows Python to be used as an Expression or Predicate in Camel routes.

For example, you can use Python in a Predicate with the Content-Based Router EIP.

Python Options

The Python language supports the following options which are listed below.

Name Default Java Type Description

resultType (common)

String

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

trim (advanced)

true

Boolean

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

resolveResource (advanced)

false

Boolean

Whether a result of the expression that is a String starting with resource: is loaded as a resource and its content becomes the result, e.g. a script that returns resource:file:order.json or resource:classpath:templates/order.json (a name without a scheme is a classpath resource). Off by default; the resource: prefix on the expression text itself is always resolved. Applies to the expression used as a value, not as a predicate.

Message Body

The message body at each side of the Python language: Expression input is the body its expressions can read, and Expression result what they return.

Side Body Description

Expression input

any

The body as it is, in the variable body: a String is a Python unicode string, and other Java objects keep their methods.

Expression result

unknown

The Java value of what the script returns: a dict as a Map, a list or a tuple as a List, a set as a Set, and None as null.

With resultType set: an object of the class it names, or null.

The bodies are the ones with the default options. A side that is not listed is not known, and tooling does not guess it. The carriers, the sides and the tools that use them are described in Message Body Types.

Variables

Variable Type Description

exchange

Exchange

the Exchange

camelContext

CamelContext

the CamelContext

exchangeId

String

the exchange id

message

Message

the message

request

Message

the message (same as message)

body

Object

the message body

header

Map

the message headers (same as headers)

headers

Map

the message headers

exchangeProperty

Map

the exchange properties (same as exchangeProperties)

exchangeProperties

Map

the exchange properties

variable

Map

the exchange variables (same as variables)

variables

Map

the exchange variables

exception

Exception

the exception if the exchange failed (or the caught exception in an error handler), otherwise None

context

CamelContext

Deprecated use camelContext

properties

Map

Deprecated use exchangeProperties

The variables have the same names as in the Groovy language, except in, which is a reserved word in Python (use message or request), and the deprecated out and response. The deprecated context and properties still work.

The variable and variables bindings are the exchange-scoped variables (for example set with the Set Variable EIP). Global and route variables, such as global:foo, are not in this map; use exchange.getVariable('global:foo') for those.

The result of a script is its Java value: None is null, a string, a number or a boolean is the Java String, number or Boolean, a dict, list, tuple or set is a Map, List or Set of Java values, and a Java object, such as the body, is returned as it is. Set resultType to convert the result to another type.

Examples

A Python predicate in a Content-Based Router:

- route:
    from:
      uri: direct:orders
      steps:
        - choice:
            when:
              - expression:
                  python:
                    expression: "headers.get('priority') == 'high'"
                steps:
                  - to:
                      uri: direct:fast
            otherwise:
              steps:
                - to:
                    uri: direct:normal

A Python expression that sets the message body from the body and a header:

- route:
    from:
      uri: direct:greet
      steps:
        - setBody:
            expression:
              python:
                expression: "'Hello ' + str(body) + ', your priority is ' + str(headers.get('priority'))"
        - to:
            uri: log:greeting

Dependencies

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

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

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