Chapter 99. MVEL Component
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:
<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
| 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. |
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");
