MVEL

Since Camel 2.12

The mvel: component allows you to process a message using an MVEL template. This can be ideal when using Templating to generate responses for requests.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-mvel</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

URI format

mvel:templateName[?options]

Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template (eg: file://folder/myfile.mvel).

You can append query options to the URI in the following format, ?option=value&option=value&…​

Options

The MVEL component has no options.

The MVEL endpoint is configured using URI syntax:

mvel:resourceUri

with the following path and query parameters:

Path Parameters (1 parameters):

Name Description Default Type

resourceUri

Required Path to the resource. You can prefix with: classpath, file, http, ref, or bean. classpath, file and http loads the resource using these protocols (classpath is default). ref will lookup the resource in the registry. bean will call a method on a bean to be used as the resource. For bean you can specify the method name after dot, eg bean:myBean.myMethod.

String

Query Parameters (3 parameters):

Name Description Default Type

contentCache (producer)

Sets whether to use resource content cache or not

false

boolean

encoding (producer)

Character encoding of the resource content.

String

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

false

boolean

Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-mvel-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 4 options, which are listed below.

Name Description Default Type

camel.component.mvel.enabled

Enable mvel component

true

Boolean

camel.component.mvel.resolve-property-placeholders

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

Boolean

camel.language.mvel.enabled

Enable mvel language

true

Boolean

camel.language.mvel.trim

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

true

Boolean

Message Headers

The mvel component sets a couple headers on the message.

Header Description

CamelMvelResourceUri

The templateName as a String object.

MVEL Context

Camel will provide exchange information in the MVEL context (just a Map). The Exchange is transfered as:

key value

exchange

The Exchange itself.

exchange.properties

The Exchange properties.

headers

The headers of the In message.

camelContext

The Camel Context intance.

request

The In message.

in

The In message.

body

The In message body.

out

The Out message (only for InOut message exchange pattern).

response

The Out message (only for InOut message exchange pattern).

Hot reloading

The mvel template resource is, by default, hot reloadable for both file and classpath resources (expanded jar). If you set contentCache=true, Camel will only load the resource once, and thus hot reloading is not possible. This scenario can be used in production, when the resource never changes.

Dynamic templates

Camel provides two headers by which you can define a different resource location for a template or the template content itself. If any of these headers is set then Camel uses this over the endpoint configured resource. This allows you to provide a dynamic template at runtime.

Header Type Description

CamelMvelResourceUri

String

A URI for the template resource to use instead of the endpoint configured.

CamelMvelTemplate

String

The template to use instead of the endpoint configured.

Samples

For example you could use something like

from("activemq:My.Queue").
  to("mvel:com/acme/MyResponse.mvel");

To use a MVEL template to formulate a response to a message for InOut message exchanges (where there is a JMSReplyTo header).

To specify what template the component should use dynamically via a header, so for example:

from("direct:in").
  setHeader("CamelMvelResourceUri").constant("path/to/my/template.mvel").
  to("mvel:dummy");

To specify a template directly as a header the component should use dynamically via a header, so for example:

from("direct:in").
  setHeader("CamelMvelTemplate").constant("@{\"The result is \" + request.body * 3}\" }").
  to("velocity:dummy");
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