[CONF] Apache ServiceMix: servicemix-script (page edited)

confluence Thu, 12 Jun 2008 07:19:02 -0700

Page Edited : SM : servicemix-script

servicemix-script has been edited by Lars Heinemann (Jun 12, 2008).

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Content:

ServiceMix Script

The ServiceMix Script component provides JBI integration with scripting engines.

Hint

There is also a JSR-223 enabled service engine for scripting. Have a look at servicemix-scripting component.

Note that this component is only available in releases >= 3.1 and older scripting component will be deprecated in future releases.
This component leverages Spring support for dynamic languages, so you will find useful informations on the Spring site.

Simple example

Here is an example of a SU deploymennt. The SU is only a zip of these two files:

xbean.xml

<beans xmlns:script="http://org.apache.servicemix/script/1.0"
       xmlns:lang="http://www.springframework.org/schema/lang"
       xmlns:test="urn:test">
  <script:exchangeProcessor service="test:groovy" endpoint="endpoint">
    <property name="helpers">
      <list>
        <ref bean="groovyExchangeHelper" />
      </list>
    </property>
    <property name="implementation" ref="groovyExchangeProcessor" />
  </script:exchangeProcessor>
  <script:exchangeHelper id="groovyExchangeHelper" singleton="true" />
  <lang:groovy id="groovyExchangeProcessor"
               script-source="classpath:GroovyExchangeProcessor.groovy">
    <lang:property name="exchangeHelper" ref="groovyExchangeHelper" />
  </lang:groovy>
</beans>


GroovyExchangeProcessor.groovy

import org.apache.servicemix.common.ExchangeProcessor;
import javax.jbi.messaging.MessageExchange;
import javax.jbi.messaging.NormalizedMessage;
import org.apache.servicemix.jbi.jaxp.StringSource;
import org.apache.servicemix.script.ScriptExchangeHelper;
import org.apache.servicemix.jbi.jaxp.SourceTransformer;

class GroovyExchangeProcessor implements ExchangeProcessor {

    @Property ScriptExchangeHelper exchangeHelper;

	def void start() {
	    println "Starting";
	}

    def void process(MessageExchange exchange) {
    	def inputMessage = new SourceTransformer().toString(exchange.getInMessage().getContent());
    	println "Hello, I got an input message "+inputMessage;
    	NormalizedMessage out = exchange.createMessage();
        out.setContent(new StringSource("<world>hello</world>"));
        exchange.setMessage(out, "out");
        exchangeHelper.sendExchange(exchange);    	
    }
    
    def void stop() {
    	println "Stopping";
    }
}


Inlining script

Alternatively, you can inline the script in the xbean.xml file the following way:


<lang:groovy id="groovyExchangeProcessor">
    <lang:inline-script><![CDATA[
        ... put your script here ...
    ]]></lang:inline-script>
    <lang:property name="exchangeHelper" ref="groovyExchangeHelper" />
  </lang:groovy>


State and threading model

The script defines a class that will be used to process incoming exchanges, but only a single instance of this class will be used.  This means that you need to make sure the script is thread safe and can be used to process requests concurrently.  On the other side, this means that maintaining state is just a matter of defining a property on the class and using it to read / store any state that will be maintained.


Script Helpers

In order to create Message Exchanges one needs the Delivery Channel to obtain the Message Exchange Factory to create them. This is not possible by default but can be easily added using a customer Script Helper class. The only thing to do is to create a class that implements the Script Helper interface and use the Script Exchange Processor Endpoint instance to obtain the Delivery Channel from. Now you can either provide the Delivery Channel as is or you can create convenience method to create Message Exchanges for example. This is how a customer Script Helper class would look like:

foo.MyScriptHelper.java

package foo;

import javax.jbi.messaging.DeliveryChannel;

import org.apache.servicemix.script.ScriptExchangeProcessorEndpoint;
import org.apache.servicemix.script.ScriptHelper;

public class MyScriptExchangeHelper
   implements ScriptHelper
{
    protected ScriptExchangeProcessorEndpoint mEndpoint;

    public void setScriptExchangeProcessorEndpoint(
        ScriptExchangeProcessorEndpoint pEndpoint
    ) {
        mEndpoint = pEndpoint;
    }

    public DeliveryChannel getChannel() {
        return mEndpoint.getChannel();
    }
}


After that you only need to use a Spring Bean to create an instance and the use the same references in the rest of the Script settings. This is what needs to be changed from the xbean.xml mentioned above:

xbean.xml changes

<bean
    id="groovyExchangeHelper"
    class="foo.MyScriptExchangeHelper"
/>

<!--<script:exchangeHelper id="groovyExchangeHelper" singleton="true" />-->


The Groovy code could then look like this:

GroovyExchangeProcessor.groovy

import org.apache.servicemix.common.ExchangeProcessor;
import javax.jbi.messaging.MessageExchange;
import org.apache.servicemix.jbi.jaxp.StringSource;
import org.apache.servicemix.script.ScriptHelper;
import org.apache.commons.logging.LogFactory;

class GroovyExchangeProcessor
    implements ExchangeProcessor
{
    @Property ScriptHelper exchangeHelper;

    def mLog = LogFactory.getLog( getClass() );

    def void start() {
        mLog.info( "Starting" );
    }

    def void process(MessageExchange pExchange) {
        def lChannel = exchangeHelper.getChannel();
        def lRequest = lChannel.createExchangeFactory().createInOutExchange();
        lRequest.setService( new QName( "urn:test", "target-service" ) );
        lRequest.setOperation( new QName( "MyOpertation" ) );
        def lNM = lRequest.createMessage();
        lNM.setContent( new StringSource( "<receiver><title>Zero</title><index>0</index></receiver>" ) );
        lRequest.setInMessage( lNM );
        mLog.info( "process() send new ME: " + lRequest );
        lChannel.send( lRequest );
    }

    def void stop() {
        mLog.info( "Stopping" );
    }
}


Sending exchanges

When acting as a Consumer (i.e. creating and sending an exchange into the bus), this Endpoint is currently limited to sending InOnly requests.  This limitation is solved for versions >= 3.2.2 
Tips when creating Script Helpers


	When defining your own helper, if you do not extend the ScriptExchangeHelper then you will need to change the type in the Groovy script to ScriptHelper for the exchangeHelper propery
	if you extend the ScriptExchangeHelper then you have to call the super.setScriptExchangeProcessorEndpoint() method in order to set the private member there too, otherwise you will experience Null Pointer Exceptions
	to use your own helper, you have to use the Spring <bean /> element in the xbean.xml as shown in the above example because the script:exchangeHelper is fixed to use the ScriptExchangeHelper class
	as Groovy is a dynamic language, there is no need to upcast the exchange helper property in the Groovy script: even though the ScriptHelper type is specified in the script, Groovy will be able to find the methods in the sub class by introspecting the object

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[CONF] Apache ServiceMix: servicemix-script (page edited)

ServiceMix Script

Simple example

Script Helpers

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