Camel Components

MVEL

Since Camel 2.0

Camel supports MVEL to do message transformations using MVEL templates.

MVEL is powerful for templates, but can also be used for Expression or Predicate

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

You can use MVEL dot notation to invoke operations. If you for instance have a body that contains a POJO that has a getFamilyName method then you can construct the syntax as follows:

request.body.familyName

Or use similar syntax as in Java:

Java-only: MVEL expression using Java method call syntax
getRequest().getBody().getFamilyName()

MVEL Options

The MVEL 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.

Variables

The following Camel related variables are made available:

Variable Type Description

this

Exchange

the Exchange is the root object

context

CamelContext

the CamelContext

exchange

Exchange

the Exchange

exchangeId

String

the exchange id

exception

Throwable

the Exchange exception (if any)

request

Message

the message

message

Message

the message

headers

Map

the message headers

header(name)

Object

the message header by the given name

header(name, type)

Type

the message header by the given name as the given type

properties

Map

the exchange properties

property(name)

Object

the exchange property by the given name

property(name, type)

Type

the exchange property by the given name as the given type

Example

For example, you could use MVEL inside a Message Filter

  • Java

  • XML

  • YAML

from("seda:foo")
  .filter().mvel("headers.foo == 'bar'")
    .to("seda:bar");
<route>
  <from uri="seda:foo"/>
  <filter>
    <mvel>headers.foo == 'bar'</mvel>
    <to uri="seda:bar"/>
  </filter>
</route>
- route:
    from:
      uri: seda:foo
      steps:
        - filter:
            expression:
              mvel:
                expression: headers.foo == 'bar'
            steps:
              - to:
                  uri: seda:bar

Loading script from external resource

You can externalize the script and have Apache 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:

Java-only: loading a MVEL script from the classpath
.setHeader("myHeader").mvel("resource:classpath:script.mvel")

Dependencies

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

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

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