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Velocity

The scalatevelocity: component allows you to process a message using Scalate template, which supports either SSP or Scaml format templatesan Apache Velocity template. This can be ideal when using Templating to generate responses for requests.

URI format

scalatevelocity: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.sspvm^{Image Modified}).

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

Options

Message Headers

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

Headers In Camel 1.4 headers set during the Scalate Velocity evaluation are returned to the message and added as headers. Then its kinda possible to return values from Scalate Velocity to the Message.

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

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

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

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Velocity Context

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

Hot reloading

The Scalate 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.

Dynamic templates

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.

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from("activemq:My.Queue").
  to("scalatevelocity:com/acme/MyResponse.sspvm");

To use a Scalate 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("scalatevelocity:com/acme/MyResponse.haml.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");

ItIn 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("CamelScalateResourceUriCamelVelocityResourceUri").constant("path/to/my/template.vm").
  to("scalatevelocity:dummy");

ItIn 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("CamelScalateTemplateCamelVelocityTemplate").constant("<%@ attribute body: Object %>\nHi Hi this is a scalatevelocity template that can do templating ${body}").
  to("scalatevelocity:dummy");

The Email Sample

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

<%@ attribute in: org.apache.camel.scala.RichMessage %>
Dear ${in("headers.lastName"}, ${in("headers.firstName)}

Thanks for the order of ${in("item")headers.item}.

Regards Camel Riders Bookstore
${in.body}

And the java code:

{snippet:id=e1|lang=java|url=camel/trunk/components/camel-velocity/src/test/java/org/apache/camel/component/velocity/VelocityLetterTest.java}