[[mvel-component]]
= MVEL Component

*Since Camel 2.12*

// HEADER START
*Only producer is supported*
// HEADER END

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).

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

== Options


// component options: START
The MVEL component supports 2 options, which are listed below.



[width="100%",cols="2,5,^1,2",options="header"]
|===
| Name | Description | Default | Type
| *lazyStartProducer* (producer) | Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. | false | boolean
| *basicPropertyBinding* (advanced) | Whether the component should use basic property binding (Camel 2.x) or the newer property binding with additional capabilities | false | boolean
|===
// 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 (5 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
| *lazyStartProducer* (producer) | Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. | false | boolean
| *basicPropertyBinding* (advanced) | Whether the endpoint should use basic property binding (Camel 2.x) or the newer property binding with additional capabilities | false | boolean
| *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




== 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:

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|=======================================================================
|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");
------------------------------------------------------------------------------------------


include::camel-spring-boot::page$mvel-starter.adoc[]
