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h3. Introduction

Because Groovy is syntactically very similar to Java, you can write your Groovy routes just like Java routes. The same Java DSL classes are being used, with the exception that some of the DSL classes get extended with a bunch of new methods at runtime. This is achieved by turning camel-groovy into a Groovy [Extension Module|http://docs.codehaus.org/display/GROOVY/Creating+an+extension+module] that defines extension methods on existing classes.

The majority of the extension methods allow [Closures|http://groovy.codehaus.org/Closures] to be used as parameters e.g. for expressions, predicates, processors. The following example reverses a string in the message body and then prints the value to System.out: 

{code:java|title=MyRouteBuilder.groovy}
...
   from('direct:test')
      .transform { it.in.body.reverse() }
      .process { println it.in.body }
...
{code}

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-groovy</artifactId>
  <version>2.11.0</version>
</dependency>
{code}

|http://groovy.codehaus.org/Groovy-Eclipse+compiler+plugin+for+Maven]:

{code:xml}
  <plugin>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
      <compilerId>groovy-eclipse-compiler</compilerId>
    </configuration>
    <dependencies>
      <dependency>
        <groupId>org.codehaus.groovy</groupId>
        <artifactId>groovy-eclipse-compiler</artifactId>
	<version>2.7.0-01</version>
      </dependency>
    </dependencies>
  </plugin>
{code}

{code:xml}
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-eclipse-plugin</artifactId>
    <configuration>
      <additionalProjectnatures>
        <projectnature>org.eclipse.jdt.groovy.core.groovyNature</projectnature>
      </additionalProjectnatures>
      <classpathContainers>
        <classpathContainer>org.eclipse.jdt.launching.JRE_CONTAINER</classpathContainer>
        <classpathContainer>GROOVY_DSL_SUPPORT</classpathContainer>
      </classpathContainers>              
    </configuration>
  </plugin>	  
{code}

h4. Using Closures in your routes

h5. Processor Closures

All Java DSL parameters of type {{

{code:java}
...
   private String someValue
...
   from('direct:test')
      .transform { it.in.body.reverse() + someValue }
      .setHeader("myHeader") { someValue.reverse() }
...
{code}


h5. Predicate Closures

All Java DSL parameters of type {{

{code:java}
...
   private String someValue

   // This time, the closure is stored in a variable
   def predicate = { Exchange e -> e.in.body != someValue }
...
   from('direct:test')
      .filter(predicate)
...
{code}


h5. Aggregation Strategy Closures

Java DSL parameters of type {{

{code:java}
...
   private String separator
...
   from('direct:test1')
      .enrich('direct:enrich') { Exchange original, Exchange resource -> 
         original.in.body += resource.in.body + separator
         original  // don't forget to return resulting exchange
      }
...
{code}


h4. Using Groovy XML processing

Groovy provides special [XML processing support|http://groovy.codehaus.

org/Processing+XML] through its {{XmlParser}}, {{XmlNodePrinter}} and {{XmlSlurper}} classes. camel-groovy provides two [data formats|data format] to use these classes directly in your routes. 

{code:java|title=Unmarshal XML with XmlParser}
...
   from('direct:test1')
      .unmarshal().gnode() 
      // message body is now of type groovy.util.Node
...
{code}

{code:java|title=Unmarshal XML with XmlSlurper}
...
   from('direct:test1')
      .unmarshal().gpath(false) // explicitly namespace-unaware
      // message body is now of type groovy.util.slurpersupport.GPathResult
...
{code}

{code:java|title=Marshal XML with XmlNodePrinter}
...
   from('direct:test1')
      // message body must be of type groovy.util.Node
      .marshal().gnode()
...
{code}


h4. Using Groovy GStrings

Groovy [GStrings|http://groovy.codehaus.org/Strings+and

+GString] are declared inside double-quotes and can contain arbitrary Groovy expressions like accessing properties or calling methods, e.g. 
{code}
def x = "It is currently ${ new Date() }"
{code}

h4. Custom DSL extensions

You can easily define your custom extensions - be it as a Java DSL extension for your Groovy routes or for any other class unrelated to Camel. All you have to do is to write your extension methods and provide a extension module descriptor - the details are described in the [Groovy documentation|http://docs.codehaus.org/display/GROOVY/Creating+an+extension+module]. And as long as you don't require other extension methods, you can even use plain Java code to achieve this!
As an example, let's write two DSL extensions to make commonly used DSL methods more concise:

{code:java|title=MyExtension.java}

import org.apache.camel.Endpoint;
import org.apache.camel.Predicate;

public final class MyExtension {
    private MyExtension() {
        // Utility Class
    }

    // Set the id of a route to its consumer URI
    public static RouteDefinition fromId(RouteDefinition delegate, String uri) {
       return delegate.from(uri).routeId(uri);
    }

    public static RouteDefinition fromId(RouteDefinition delegate, Endpoint endpoint) {
       return delegate.from(endpoint).routeId(endpoint.getEndpointUri());
    }

    // Make common choice pattern more concise

    public static ProcessorDefinition<?> fork(ProcessorDefinition<?> delegate, String uri1, String uri2, Predicate predicate) {
       return delegate.choice().when(predicate).to(uri1).otherwise().to(uri2);
    }

}
{code}

}
...
   fromId('direct:test1')
      .fork('direct:null','direct:not-null',body().isNull())
...
{code}

}
...
   from("direct:test1")
      .routeId("direct:test1")
      .choice()
         .when(body().isNull())
            .to("direct:null")
         .otherwise()
            .to("direct:not-null");
...
{code}