Velocity

The velocity: component allows you to process a message using an Apache Velocity template. This can be ideal when using Templating to generate responses for requests.

URI format

velocity:templateName

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).

Options

Option	Default	Description
loaderCache	true	Velocity based file loader cache
contentCache		New option in Camel 1.4. Cache for the resource content when its loaded. Is default false in Camel 1.x. Is default true in Camel 2.x.
encoding	null	New option in Camel 1.6. Character encoding of the resource content.

Headers

Camel will store a reference to the resource in the message header in the key org.apache.camel.velocity.resource. The Resource is an org.springframework.core.io.Resource object.

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

An example: Set the header value of fruit in the Velocity template .tm:

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

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

Velocity Context

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

key	value
exchange	The Exchange itself
headers	The headers of the in message
camelContext	The Camel Context
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 velocity template resource is by default hot reloadable for both file and classpath resources (expanded jar). Setting the contentCache=true then Camel will only load the resource once, and thus hot reloading is not possible. This scenario can be used in production usage when the resource never changes.

Samples

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 for 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

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

And to use content cache, eg. for production usage 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");

The Email Sample

In this sample we want to use Velocity as 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:

Error formatting macro: snippet: java.lang.NullPointerException

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