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. |
Message Headers
Header |
Description |
---|---|
|
Camel 1.x: The resource as an |
|
Camel 1.x: The templateName as String object. |
|
Camel 2.0: The resource as an |
|
Camel 2.0: The templateName as String 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: