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:
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<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>
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string-template:templateName[?options]
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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
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Option | Default | Description |
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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 |
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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, 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
Camel will provide exchange information as attributes (just a java.util.Map) to the string template. The Exchange is transfered as:
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key | value |
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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). |
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Since Camel 2.14, you can define the custom context map by setting the message header "CamelStringTemplateVariableMap" just like the below code.
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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);
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Samples
For example you could use a string template as follows in order to formulate a response to a message:
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from("activemq:My.Queue").
to("string-template:com/acme/MyResponse.tm");
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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 $.
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Dear <headers.lastName>, <headers.firstName>
Thanks for the order of <headers.item>.
Regards Camel Riders Bookstore
<body>
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And the java code is as follows:
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{snippet:id=e1|lang=java|url=camel/trunk/components/camel-stringtemplate/src/test/java/org/apache/camel/component/stringtemplate/StringTemplateLetterTest.java} |
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