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Chapter 171. 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 |
|---|---|---|
allowContextMapAll (producer)
|
false
|
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 imposes a potential security risk as this opens access to the full power of CamelContext API.
|
allowTemplateFromHeader (producer)
|
false
|
Whether to allow to use resource template from header or not (default false). Enabling this option has security ramifications. For example, if the header contains untrusted or user derived content, this can ultimately impact on the confidentility and integrity of your end application, so use this option with caution.
|
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");
}
};
}