Camel Component: Freemarker - 6.3

Talend ESB Mediation Developer Guide

EnrichVersion
6.3
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Talend Data Fabric
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Talend MDM Platform
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task
Design and Development
EnrichPlatform
Talend ESB

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>
   <!-- use the same version as your Camel core version -->
   <version>x.x.x</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 (for example: 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 it is loaded. Note: Cached resource content can be cleared via JMX using the endpoint's clearContentCache operation.

encoding

null

Character encoding of the resource content.

templateUpdateDelay

5

Character encoding of the resource content.

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:

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).

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.

Header

Type

Description

FreemarkerConstants. FREEMARKER_RESOURCE_URI

String

A URI for the template resource to use instead of the endpoint configured.

FreemarkerConstants. FREEMARKER_TEMPLATE

String

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");

To disable the content cache, for example, 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");

A file-based resource:

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

In it is 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");