The string-template: component allows you to process a message using a String 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-stringtemplate</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

string-template:templateName[?options]

Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template.

You can append query options to the URI in the following format, ?option=value&option=value&...

Fuse Mediation Router will store a reference to the resource in the message header with key, org.apache.camel.stringtemplate.resource. The Resource is an org.springframework.core.io.Resource object.

The string template resource is by default hot-reloadable for both file and classpath resources (expanded jar). If you set contentCache=true, Fuse Mediation Router loads the resource only once and hot-reloading is not possible. This scenario can be used in production when the resource never changes.

Fuse Mediation Router will provide exchange information as attributes (just a java.util.Map) to the string template. The Exchange is transfered as:

For example you could use a string template as follows in order to formulate a response to a message:

from("activemq:My.Queue").
  to("string-template:com/acme/MyResponse.tm");

In this sample we want to use a string template to send an order confirmation email. The email template is laid out in StringTemplate as:

Dear $headers.lastName$, $headers.firstName$

Thanks for the order of $headers.item$.

Regards Camel Riders Bookstore
$body$

And the java code is as follows:

private Exchange createLetter() {
    Exchange exchange = context.getEndpoint("direct:a").createExchange();
    Message msg = exchange.getIn();
    msg.setHeader("firstName", "Claus");
    msg.setHeader("lastName", "Ibsen");
    msg.setHeader("item", "Camel in Action");
    msg.setBody("PS: Next beer is on me, James");
    return exchange;
}

@Test
public void testVelocityLetter() throws Exception {
    MockEndpoint mock = getMockEndpoint("mock:result");
    mock.expectedMessageCount(1);
    mock.expectedBodiesReceived("Dear Ibsen, Claus! Thanks for the order of Camel in Action. Regards Camel Riders Bookstore PS: Next beer is on me, James");

    template.send("direct:a", createLetter());

    mock.assertIsSatisfied();
}

protected RouteBuilder createRouteBuilder() throws Exception {
    return new RouteBuilder() {
        public void configure() throws Exception {
            from("direct:a").to("string-template:org/apache/camel/component/stringtemplate/letter.tm").to("mock:result");
        }
    };
}