Chapter 132. Velocity

Velocity
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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
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velocity:templateName[?options]

velocity:templateName[?options]

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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&...

Options
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Option	Default	Description
`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.

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

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key	value
`exchange`	The `Exchange` itself.
`exchange.properties`	The `Exchange` properties.
`headers`	The headers of the In message.
`camelContext`	The Camel Context intance.
`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).

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.

Dynamic templates
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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.

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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.

Samples
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For example you could use something like

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

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

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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");

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

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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");

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

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And a file based resource:

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

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

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

from("direct:in").
  setHeader("CamelVelocityResourceUri").constant("path/to/my/template.vm").
  to("velocity:dummy");

from("direct:in").
  setHeader("CamelVelocityResourceUri").constant("path/to/my/template.vm").
  to("velocity:dummy");

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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:

from("direct:in").
  setHeader("CamelVelocityTemplate").constant("Hi this is a velocity template that can do templating ${body}").
  to("velocity:dummy");

from("direct:in").
  setHeader("CamelVelocityTemplate").constant("Hi this is a velocity template that can do templating ${body}").
  to("velocity:dummy");

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The Email Sample
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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}

Dear ${headers.lastName}, ${headers.firstName}

Thanks for the order of ${headers.item}.

Regards Camel Riders Bookstore
${body}

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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;
}

@Test
public void testVelocityLetter() throws Exception {
    MockEndpoint mock = getMockEndpoint("mock:result");
    mock.expectedMessageCount(1);
    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());

    mock.assertIsSatisfied();
}

protected RouteBuilder createRouteBuilder() throws Exception {
    return new RouteBuilder() {
        public void configure() throws Exception {
            from("direct:a").to("velocity:org/apache/camel/component/velocity/letter.vm").to("mock:result");
        }
    };
}

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;
}

@Test
public void testVelocityLetter() throws Exception {
    MockEndpoint mock = getMockEndpoint("mock:result");
    mock.expectedMessageCount(1);
    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());

    mock.assertIsSatisfied();
}

protected RouteBuilder createRouteBuilder() throws Exception {
    return new RouteBuilder() {
        public void configure() throws Exception {
            from("direct:a").to("velocity:org/apache/camel/component/velocity/letter.vm").to("mock:result");
        }
    };
}

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Velocity
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URI format
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Options
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Velocity Context
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Hot reloading
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Dynamic templates
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Samples
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The Email Sample
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Velocity
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URI format
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Options
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Velocity Context
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Hot reloading
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Dynamic templates
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Samples
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The Email Sample
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