Chapter 148. StringTemplate
String Template
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>URI format
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&...
Options
| Option | Default | Description |
|---|---|---|
contentCache
|
false
|
Cache for the resource content when its loaded. Note : as of Camel 2.9 cached resource content can be cleared via JMX using the endpoint's clearContentCache operation.
|
delimiterStart
|
null
|
Since Camel 2.11.1, configuring the variable start delimiter |
delimiterStop
|
null
|
Since Camel 2.11.1, configuring the variable end delimiter |
Headers
Apache Camel 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.
Hot reloading
The string template resource is by default hot-reloadable for both file and classpath resources (expanded jar). If you set
contentCache=true, Apache Camel loads the resource only once and hot-reloading is not possible. This scenario can be used in production when the resource never changes.
StringTemplate Attributes
Apache Camel will provide exchange information as attributes (just a
java.util.Map) to the string template. The Exchange is transfered as:
| key | value |
|---|---|
exchange
|
The Exchange itself. |
headers
|
The headers of the In message. |
camelContext
|
The Camel Context. |
request
|
The In message. |
in
|
The In message. |
body
|
The In message body. |
out
|
The Out message (only for InOut message exchange pattern). |
response
|
The Out message (only for InOut message exchange pattern). |
Since Camel 2.14, you can define the custom context map by setting the message header "CamelStringTemplateVariableMap" just like the below code.
Map<String, Object> variableMap = new HashMap<String, Object>();
Map<String, Object> headersMap = new HashMap<String, Object>();
headersMap.put("name", "Willem");
variableMap.put("headers", headersMap);
variableMap.put("body", "Monday");
variableMap.put("exchange", exchange);
exchange.getIn().setHeader("CamelStringTemplateVariableMap", variableMap);
Samples
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");The Email Sample
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: This example works for camel 2.11.0. If your camel version is less than 2.11.0, the variables should be started and ended with $.
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");
}
};
}