FreeMarker

The freemarker: component allows for processing 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

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|| Option || Default || Description ||
| {{contentCache}} | {{true}} | Cache for the resource content when it's 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. |
| {{templateUpdateDelay}} | {{5}} | *Camel 2.9:* Number of seconds the loaded template resource will remain in the cache. | 
{div}

Headers

Headers set during the FreeMarker evaluation are returned to the message and added as headers. This provides a mechanism for the FreeMarker component to return values 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 transferred 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. |
| {{request}} | The In message. |
| {{body}} | The In message body. | 
| {{response}} | The Out message (only for InOut message exchange pattern). |
{div}

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

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 || Support Version ||
| FreemarkerConstants.FREEMARKER_RESOURCE | org.springframework.core.io.Resource | The template resource | <= 2.1 |
| FreemarkerConstants.FREEMARKER_RESOURCE_URI | String | A URI for the template resource to use instead of the endpoint configured. | >= 2.1 |
| FreemarkerConstants.FREEMARKER_TEMPLATE | String | The template to use instead of the endpoint configured. | >= 2.1 |
{div}

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(FreemarkerConstants.FREEMARKER_RESOURCE_URI).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:

{snippet:id=e1|lang=java|url=camel/trunk/components/camel-freemarker/src/test/java/org/apache/camel/component/freemarker/FreemarkerLetterTest.java}