[[mvel-component]]
== MVEL Component

*Available as of Camel version 2.12*

The *mvel:* component allows you to process a message using an
http://mvel.codehaus.org/[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:

[source,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

[source,java]
---------------------------
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[file://folder/myfile.mvel]).

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

### Options


// component options: START
The MVEL component has no options.
// component options: END




// endpoint options: START
The MVEL endpoint is configured using URI syntax:

----
mvel:resourceUri
----

with the following path and query parameters:

==== Path Parameters (1 parameters):


[width="100%",cols="2,5,^1,2",options="header"]
|===
| 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):


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|===
| 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
|===
// endpoint options: END
// spring-boot-auto-configure options: START
=== Spring Boot Auto-Configuration

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

[source,xml]
----
<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.



[width="100%",cols="2,5,^1,2",options="header"]
|===
| 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
|===
// spring-boot-auto-configure options: END




### Message Headers

The mvel component sets a couple headers on the message.

[width="100%",cols="10%,90%",options="header",]
|=======================================================================
|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:

[width="100%",cols="10%,90%",options="header",]
|=======================================================================
|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.

[width="100%",cols="10%,10%,80%",options="header",]
|=======================================================================
|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

[source,java]
--------------------------------------
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:

[source,java]
-------------------------------------------------------------------------
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:

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

### See Also

* Configuring Camel
* Component
* Endpoint
* Getting Started
