Chapter 363. Velocity Component

velocity: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.vm).

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

The Velocity component supports 4 options, which are listed below.

The Velocity endpoint is configured using URI syntax:

velocity:resourceUri

with the following path and query parameters:

The component supports 3 options, which are listed below.

The velocity component sets a couple headers on the message (you can’t set these yourself and from Camel 2.1 velocity component will not set these headers which will cause some side effect on the dynamic template support):

Headers set during the Velocity evaluation are returned to the message and added as headers. Then its kinda possible to return values from Velocity to the Message.

For example, to set the header value of fruit in the Velocity template .tm:

$in.setHeader("fruit", "Apple")

The fruit header is now accessible from the message.out.headers.

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

Since Camel-2.14, you can setup a custom Velocity Context yourself by setting the message header *CamelVelocityContext *just like this

   VelocityContext velocityContext = new VelocityContext(variableMap);
   exchange.getIn().setHeader("CamelVelocityContext", velocityContext);

The Velocity 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.

Available as of Camel 2.1
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.

For example you could use something like

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

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

If you want to use InOnly and consume the message and send it to another destination, you could use the following route:

from("activemq:My.Queue").
  to("velocity:com/acme/MyResponse.vm").
  to("activemq:Another.Queue");

And to use the content cache, e.g. for use in production, where the .vm template never changes:

from("activemq:My.Queue").
  to("velocity:com/acme/MyResponse.vm?contentCache=true").
  to("activemq:Another.Queue");

And a file based resource:

from("activemq:My.Queue").
  to("velocity:file://myfolder/MyResponse.vm?contentCache=true").
  to("activemq:Another.Queue");

In Camel 2.1 it’s possible to specify what template the component should use dynamically via a header, so for example:

from("direct:in").
  setHeader("CamelVelocityResourceUri").constant("path/to/my/template.vm").
  to("velocity:dummy?allowTemplateFromHeader=true");

In Camel 2.1 it’s possible to specify a template directly as a header the component should use dynamically via a header, so for example:

from("direct:in").
  setHeader("CamelVelocityTemplate").constant("Hi this is a velocity template that can do templating ${body}").
  to("velocity:dummy?allowTemplateFromHeader=true");

In this sample we want to use Velocity templating for an order confirmation email. The email template is laid out in Velocity as:

Dear ${headers.lastName}, ${headers.firstName}

Thanks for the order of ${headers.item}.

Regards Camel Riders Bookstore
${body}

And the java code: