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:
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URI format
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Where templateName is the classpath-local
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URI
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of
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the
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template
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to
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invoke;
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or
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the
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complete
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URL
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of
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the
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remote
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template
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(eg:
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You
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can
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append
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query
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options
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to
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the
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URI
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in
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the
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following
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format,
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?option=value&option=value&...
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Options
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Option | Default | Description |
|---|---|---|
| | Cache for the resource content when it's loaded. |
| | Character encoding of the resource content. |
| | Camel 2.9: Number of seconds the loaded template resource will remain in the cache. |
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:
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The header,
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fruit
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,
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is
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now
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accessible
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from
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the
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message.out.headers
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.
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 |
|---|---|
| The |
| The |
| The headers of the In message. |
| The Camel Context. |
| The In message. |
| The In message body. |
| 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
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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 |
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The |
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template |
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resource |
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<= |
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2.1 |
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FreemarkerConstants.FREEMARKER_RESOURCE_URI |
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String | A URI for the template resource to use instead of the endpoint configured. | >= 2.1 | |
FreemarkerConstants.FREEMARKER_TEMPLATE |
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String | The template to use instead of the endpoint configured. | >= 2.1 |
Samples
For example you could use something like:
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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:
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And to disable the content cache, e.g.
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for
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development
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usage
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where
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the
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.ftl
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template
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should
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be
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hot
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reloaded:
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And a file-based
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resource:
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In Camel 2.1
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it's
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possible
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to
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specify
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what
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template
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the
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component
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should
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use
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dynamically
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via
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a
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header,
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so
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for
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example:
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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:
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And the java code:
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