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[CONF] Apache Camel > Freemarker

confluence Sun, 28 Mar 2010 18:06:24 -0700

Freemarker

Page edited by willem jiang

Freemarker

Available as of Camel 1.6

The freemarker: component allows you to process a message using a Freemarker template. This can be ideal when using Templating to generate responses for requests.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-freemarker</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>


URI format


freemarker: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.ftl).

You can append query options to the URI in the following format, ?option=value&option=value&...

Options



 Option 
 Default 
 Description 


 contentCache 
 true 
 Cache for the resource content when its loaded. 


 encoding 
 null 
 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.freemarker.resource. The Resource is an org.springframework.core.io.Resource object. And the key org.apache.camel.freemarker.resourceUri holds the templateName as a String object. 

Note From Camel 2.1 and Camel 1.6.2, freemarker endpoint will not store these headers into to message, as these header will cause some side effect on the dynamic templates feature. 

Headers set during the Freemarker evaluation are returned to the message and added as headers. Then its kinda possible to return values from Freemarker to the Message.

An example: Set the header value of fruit in the Freemarker template:

${request.setHeader('fruit', 'Apple')}



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

Freemarker Context
Camel will provide exchange information in the Freemarker 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. 


 body 
 The In message body. 


 response 
 The Out message (only for InOut message exchange pattern). 



Hot reloading
The Freemarker template resource is by default not hot reloadable for both file and classpath resources (expanded jar). If you set contentCache=false, then Camel will not cache the resource and hot reloading is thus enabled. This scenario can be used in development.

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 


 CamelFreemarkerResourceUri 
 String 
 Camel 2.1: A URI for the template resource to use instead of the endpoint configured. 


 CamelFreemarkerTemplate 
 String 
 Camel 2.1: The template to use instead of the endpoint configured. 




Samples

For example you could use something like:


from("activemq:My.Queue").
  to("freemarker:com/acme/MyResponse.ftl");



To use a Freemarker 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("freemarker:com/acme/MyResponse.ftl").
  to("activemq:Another.Queue");



And to disable the content cache, e.g. for development usage where the .ftl template should be hot reloaded:


from("activemq:My.Queue").
  to("freemarker:com/acme/MyResponse.ftl?contentCache=false").
  to("activemq:Another.Queue");



And a file-based resource:

from("activemq:My.Queue").
  to("freemarker:file://myfolder/MyResponse.ftl?contentCache=false").
  to("activemq:Another.Queue");



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("CamelFreemarkerResourceUri").constant("path/to/my/template.ftl").
  to("freemarker:dummy");



The Email Sample
In this sample we want to use Freemarker templating for an order confirmation email. The email template is laid out in Freemarker as:

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

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

Regards Camel Riders Bookstore
${body}



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 testFreemarkerLetter() 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("freemarker:org/apache/camel/component/freemarker/letter.ftl").to("mock:result");
        }
    };
}



See Also

	Configuring Camel
	Component
	Endpoint
	Getting Started

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