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Chapter 180. 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

Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template (for example, file://folder/myfile.vm).
You can append query options to the URI in the following format, ?option=value&option=value&...


Option Default Description
allowTemplateFromHeader false Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care.
loaderCache true Velocity based file loader cache.
contentCache true Cache for the resource content when it is loaded. Note : as of Camel 2.9 cached resource content can be cleared via JMX using the endpoint's clearContentCache operation.
encoding null Character encoding of the resource content.
propertiesFile null New option in Camel 2.1: The URI of the properties file which is used for VelocityEngine initialization.

Message headers

The velocity component sets a couple headers on the message (you can't set these yourself and from Camel 2.1 velocity component will not set these headers which will cause some side effect on the dynamic template support):
CamelVelocityResourceUriThe templateName as a String object.
CamelVelocitySupplementalContextCamel 2.16: To add additional information to the used VelocityContext. The value of this header should be a Map with key/values that will be added (overriding any existing key with the same name). This can be used to preset some common key/values you want to reuse in your velocity endpoints.
Headers set during the Velocity evaluation are returned to the message and added as headers. Then it is effectively possible to return values from Velocity to the Message. For example, to set the header value of fruit in the Velocity template,
$in.setHeader("fruit", "Apple")
The fruit header is now accessible from the message.out.headers.

Velocity Context

Apache Camel will provide exchange information in the Velocity context (just a Map). The Exchange is transfered as:
key value
exchange The Exchange itself. The Exchange properties.
headers The headers of the In message.
camelContext The Camel Context instance.
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).
Since Camel-2.14, you can setup a custom Velocity Context yourself by setting the message header CamelVelocityContext just like this
VelocityContext velocityContext = new VelocityContext(variableMap);
exchange.getIn().setHeader("CamelVelocityContext", velocityContext);

Hot reloading

The Velocity template resource is, by default, hot reloadable for both file and classpath resources (expanded jar). If you set contentCache=true, Apache 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.
Velocity can load the resource file from the Registry by using ref: as prefix.

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


For example you could use something like
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:
And to use the content cache, e.g. for use in production, where the .vm template never changes:
And a file based resource:
In Camel 2.1 it's possible to specify what template the component should use dynamically via a header, so for example:
In 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:
  setHeader("CamelVelocityTemplate").constant("Hi this is a velocity template that can do templating ${body}").

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
And the java code:
private Exchange createLetter() {
    Exchange exchange = context.getEndpoint("direct:a").createExchange();
    Message msg = exchange.getIn();
    msg.setHeader("firstName", "Claus");
    msg.setHeader("lastName", "Ibsen");
    msg.setHeader("item", "Camel in Action");
    msg.setBody("PS: Next beer is on me, James");
    return exchange;

public void testVelocityLetter() throws Exception {
    MockEndpoint mock = getMockEndpoint("mock:result");
    mock.expectedBodiesReceived("Dear Ibsen, Claus\n\nThanks for the order of Camel in Action.\n\nRegards Camel Riders Bookstore\nPS: Next beer is on me, James");

    template.send("direct:a", createLetter());


protected RouteBuilder createRouteBuilder() throws Exception {
    return new RouteBuilder() {
        public void configure() throws Exception {