Chapter 106. Freemarker Component

Available as of Camel version 2.10

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>

106.1. 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&…​

106.2. Options

The Freemarker component supports 2 options which are listed below.

NameDescriptionDefaultType

configuration (advanced)

To use an existing freemarker.template.Configuration instance as the configuration.

 

Configuration

resolveProperty Placeholders (advanced)

Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.

true

boolean

The Freemarker endpoint is configured using URI syntax:

freemarker:resourceUri

with the following path and query parameters:

106.2.1. Path Parameters (1 parameters):

NameDescriptionDefaultType

resourceUri

Required Path to the resource. You can prefix with: classpath, file, http, ref, or bean. classpath, file and http loads the resource using these protocols (classpath is default). ref will lookup the resource in the registry. bean will call a method on a bean to be used as the resource. For bean you can specify the method name after dot, eg bean:myBean.myMethod.

 

String

106.2.2. Query Parameters (5 parameters):

NameDescriptionDefaultType

configuration (producer)

Sets the Freemarker configuration to use

 

Configuration

contentCache (producer)

Sets whether to use resource content cache or not

false

boolean

encoding (producer)

Sets the encoding to be used for loading the template file.

 

String

templateUpdateDelay (producer)

Number of seconds the loaded template resource will remain in the cache.

 

int

synchronous (advanced)

Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).

false

boolean

106.3. 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.

106.4. FreeMarker Context

Camel will provide exchange information in the FreeMarker context (just a Map). The Exchange is transferred as:

keyvalue

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).

From Camel 2.14, you can setup your custom FreeMarker context in the message header with the key "CamelFreemarkerDataModel" just like this

Map<String, Object> variableMap = new HashMap<String, Object>();
variableMap.put("headers", headersMap);
variableMap.put("body", "Monday");
variableMap.put("exchange", exchange);
exchange.getIn().setHeader("CamelFreemarkerDataModel", variableMap);

106.5. 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.

106.6. 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.

HeaderTypeDescriptionSupport 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

106.7. 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");

106.8. 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:

106.9. See Also

  • Configuring Camel
  • Component
  • Endpoint
  • Getting Started