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[?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&...
Options
Option |
Default |
Description |
---|---|---|
|
|
Velocity based file loader cache. |
|
|
New option in Camel 1.4: Cache for the resource content when it is loaded. By default, it's |
|
|
New option in Camel 1.6: Character encoding of the resource content. |
Message Headers
The velocity component sets a couple headers on the message (you can't set these yourself):
Header |
Description |
---|---|
|
Camel 1.x: The resource as an |
|
Camel 1.x: The templateName as a |
|
Camel 2.0: The resource as an |
|
Camel 2.0: The templateName as a |
In Camel 1.4 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
.
Velocity Context
Camel will provide exchange information in the Velocity context (just a Map
). The Exchange
is transfered as:
key |
value |
---|---|
|
The |
|
The headers of the In message. |
|
The Camel Context intance. |
|
The In message. |
|
The In message. |
|
The In message body. |
|
The Out message (only for InOut message exchange pattern). |
|
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). 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.
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 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");
The Email Sample
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: