Freemarker
Since Camel 2.10
Only producer is supported
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
The Freemarker component supports 5 options, which are listed below.
Name | Description | Default | Type |
---|---|---|---|
allowContextMapAll (producer) |
Sets whether the context map should allow access to all details. By default only the message body and headers can be accessed. This option can be enabled for full access to the current Exchange and CamelContext. Doing so impose a potential security risk as this opens access to the full power of CamelContext API. |
false |
boolean |
allowTemplateFromHeader (producer) |
Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care. |
false |
boolean |
lazyStartProducer (producer) |
Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. |
false |
boolean |
autowiredEnabled (advanced) |
Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. |
true |
boolean |
configuration (advanced) |
To use an existing freemarker.template.Configuration instance as the configuration. |
Configuration |
The Freemarker endpoint is configured using URI syntax:
freemarker:resourceUri
with the following path and query parameters:
Path Parameters (1 parameters):
Name | Description | Default | Type |
---|---|---|---|
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 |
Query Parameters (8 parameters):
Name | Description | Default | Type |
---|---|---|---|
allowContextMapAll (producer) |
Sets whether the context map should allow access to all details. By default only the message body and headers can be accessed. This option can be enabled for full access to the current Exchange and CamelContext. Doing so impose a potential security risk as this opens access to the full power of CamelContext API. |
false |
boolean |
allowTemplateFromHeader (producer) |
Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care. |
false |
boolean |
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 |
|
lazyStartProducer (producer) |
Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. |
false |
boolean |
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 |
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 |
---|---|
|
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). |
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);
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 |
org.springframework.core.io.Resource |
The template resource. |
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");
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");
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?allowTemplateFromHeader=true");
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:
Spring Boot Auto-Configuration
When using freemarker with Spring Boot make sure to use the following Maven dependency to have support for auto configuration:
<dependency>
<groupId>org.apache.camel.springboot</groupId>
<artifactId>camel-freemarker-starter</artifactId>
<version>x.x.x</version>
<!-- use the same version as your Camel core version -->
</dependency>
The component supports 6 options, which are listed below.
Name | Description | Default | Type |
---|---|---|---|
camel.component.freemarker.allow-context-map-all |
Sets whether the context map should allow access to all details. By default only the message body and headers can be accessed. This option can be enabled for full access to the current Exchange and CamelContext. Doing so impose a potential security risk as this opens access to the full power of CamelContext API. |
false |
Boolean |
camel.component.freemarker.allow-template-from-header |
Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care. |
false |
Boolean |
camel.component.freemarker.autowired-enabled |
Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. |
true |
Boolean |
camel.component.freemarker.configuration |
To use an existing freemarker.template.Configuration instance as the configuration. The option is a freemarker.template.Configuration type. |
Configuration |
|
camel.component.freemarker.enabled |
Whether to enable auto configuration of the freemarker component. This is enabled by default. |
Boolean |
|
camel.component.freemarker.lazy-start-producer |
Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. |
false |
Boolean |