Grails: Intercepting Service class methods

It took me a little while to fully understand how to add some kind of interceptor to a Grails Service class and I wanted to add a blog post incase others have a similar question. After doing some research, and piecing together information from various sites I ended up with the information here. I hope it is helpful to you.

What problem am I trying to solve?
Adding interceptors to Controllers is really easy and I wanted to add some interceptors to my Service classes in a similar fashion. But it appears that you cannot do this for Service classes - just Controller classes. If I am wrong, please someone show me how best to do this.

Why am I trying to do this?
I use Flex in many of my application implementations and I use BlazeDS/AMF in many of the cases. I needed to add a security check on every exposed Flex service.

How did I do this?
In my service class I added a custom property that I called 'secureService'. But as you will see you can use anything.

 class TeslaService {  
   boolean transactional = true  
  // secureService is a custom property that is looked for in the BootStrap.groovy file and if  
  // found in a ServiceClass, then it modifies the invokeMethod to add some code before and  
  // after the call.  
   boolean secureService = true  
   def serviceMethod() {  
    println 'Tesla Service Method called'  
   }  
 }  

Next I updated my BootStrap.groovy file and for each ServiceClass, checked for the 'secureService' property being set to true. If it was, I then used the MetaClass InvokeMethod and assigned a new closure that could add a security check.

The updated bootstrap file looked like the following:

 class BootStrap {  
    def grailsApplication  
    def init = { servletContext ->  
    grailsApplication.serviceClasses.each {  
     def isSecured = it.getPropertyValue('secureService')  
     if( isSecured ) {  
      // example of how to 'intercept' service classes.  
      it.metaClass.invokeMethod = { name, args ->  
       println '''SECURE before $name'''  
       def res = delegate.metaClass.getMetaMethod(name,args).invoke( delegate, args)  
       println '''SECURE after $name. res=$res'''  
       res  
      }  
     }  
    }  
    }  
    def destroy = {  
    }  
 }   

To test this I created an Integration test. This test looked like the following:

 class TeslaServiceIntegrationTests extends GrailsUnitTestCase {  
  def teslaService  
   protected void setUp() {  
     super.setUp()  
   }  
   protected void tearDown() {  
     super.tearDown()  
   }  
   void testServiceMethod() {  
    teslaService.serviceMethod()  
   }  
 }  

The output of this was the following:
SECURE before serviceMethod
Tesla Service Method called
SECURE after serviceMethod. res=null

Some of the links that I used are below as the information from these posts might also be helpful to you.

http://www.pubbs.net/grails/201001/9868/
http://mrhaki.blogspot.com/2010/01/grails-goodness-access-grails.html
http://www.grails.org/doc/latest/api/org/codehaus/groovy/grails/commons/ClassPropertyFetcher.html