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Scalate

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

URI format

velocityscalate: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.vmssp^{Image Modified}).

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

Options

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Option

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Default

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Description

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loaderCache

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true

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Velocity based file loader cache.

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contentCache

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encoding

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null

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New option in Camel 1.6: Character encoding of the resource content.

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propertiesFile

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null

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New option in Camel 2.1: The URI of the properties file which is used for VelocityEngine initialization.

Message Headers

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

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

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

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

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

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Scalate Context

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

Hot reloading

The Velocity Scalate 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

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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
CamelVelocityResourceUri CamelScalateResourceUri	String	Camel 2.1: A URI for the template resource to use instead of the endpoint configured.
CamelVelocityTemplate CamelScalateTemplate	String	Camel 2.1: The template to use instead of the endpoint configured.

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Code Block
from("activemq:My.Queue"). to("velocityscalate:com/acme/MyResponse.vmssp");

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

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Code Block
from("activemq:My.Queue"). to("velocityscalate:com/acme/MyResponse.vmhaml"). to("activemq:Another.Queue");

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

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

And a file based resource:

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

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

Code Block
from("direct:in"). setHeader("CamelVelocityResourceUriCamelScalateResourceUri").constant("path/to/my/template.vm"). to("velocityscalate:dummy");

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

Code Block
from("direct:in"). setHeader("CamelVelocityTemplateCamelScalateTemplate").constant("Hi<%@ attribute body: Object %>\nHi this is a velocityscalate template that can do templating ${body}"). to("velocityscalate:dummy");

The Email Sample

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

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

Thanks for the order of ${headers.itemin("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}