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Comment: Migration of unmigrated content due to installation of a new plugin

MVEL Component

Available as of 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:

Code Block
xml
xml
<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

Code Block
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

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{div:class=confluenceTableSmall}
|| Option || Default || Description ||
| {{contentCache}} | {{true}} | Cache for the resource content when it is loaded. The cached resource content can be cleared via JMX using the endpoint's {{clearContentCache}} operation. |
| {{encoding}} | {{null}} | Character encoding of the resource content. |
{div}

Message Headers

The mvel component sets a couple headers on the message.

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{div:class=confluenceTableSmall}
|| Header || Description ||
| {{CamelMvelResourceUri}} | The *templateName* as a {{String}} object. |
{div}

MVEL Context

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

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{div:class=confluenceTableSmall}
|| 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). |
{div}

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.

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{div:class=confluenceTableSmall}
|| 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. |
{div}

Samples

For example you could use something like

Code Block
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:

Code Block
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:

Code Block
from("direct:in").
  setHeader("CamelMvelTemplate").constant("@{\"The result is \" + request.body * 3}\" }").
  to("velocity:dummy");
Include Page
Endpoint See Also
Endpoint See Also