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Chapter 157. Spark REST

Spark REST Component
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Available as of Camel 2.14
The Spark-rest component allows to define REST endpoints using the Spark REST Java library using the Rest DSL.
Important
Spark Java requires Java 8 runtime.
Maven users will need to add the following dependency to their pom.xml for this component: 
<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-spark-rest</artifactId>
    <version>${camel-version}</version>
</dependency>
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URI format
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spark-rest://verb:path?[options]
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URI Options
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Expand
Name
Default Value
Description
verb
get, post, put, patch, delete, head, trace, connect, or options.
path
the content path which support Spark syntax. See further below for examples.
accept
accept type such as: 'text/xml', or 'application/json'. By default we accept all kinds of types.

Path using Spark syntax
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The path option is defined using a Spark REST syntax where you define the REST context path using support for parameters and splat. See more details at the Spark Java Route documentation.
The following is a Camel route using a fixed path 
  from("spark-rest:get:hello")
    .transform().constant("Bye World");
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And the following route uses a parameter which is mapped to a Camel header with the key "me". 
  from("spark-rest:get:hello/:me")
    .transform().simple("Bye ${header.me}");
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Mapping to Camel Message
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The Spark Request object is mapped to a Camel Message as a org.apache.camel.component.sparkrest.SparkMessage which has access to the raw Spark request using the getRequest method. By default the Spark body is mapped to Camel message body, and any HTTP headers / Spark parameters is mapped to Camel Message headers. There is special support for the Spark splat syntax, which is mapped to the Camel message header with key splat.
For example the given route below uses Spark splat (the asterisk sign) in the context path which we can access as a header form the Simple language to construct a response message. 
  from("spark-rest:get:/hello/*/to/*")
    .transform().simple("Bye big ${header.splat[1]} from ${header.splat[0]}");
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Rest DSL
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Apache Camel provides a new Rest DSL that allow to define the REST services in a nice REST style. For example we can define a REST hello service as shown below: 
  return new RouteBuilder() {
      @Override
      public void configure() throws Exception {
            rest("/hello/{me}").get()
                .route().transform().simple("Bye ${header.me}");
        }
    };
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  <camelContext xmlns="http://camel.apache.org/schema/spring">
    <rest uri="/hello/{me}">
      <get>
        <route>
          <transform>
            <simple>Bye ${header.me}</simple>
          </transform>
        </route>
      </get>
    </rest>
  </camelContext>
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See more details at the Rest DSL.

More examples
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There is a camel-example-spark-rest-tomcat example in the Apache Camel distribution, that demonstrates how to use camel-spark-rest in a web application that can be deployed on Apache Tomcat, or similar web containers.
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