CAF getting Null pointer exception for a Application service

i All.

I am trying to develop a Composite Application in NWDS. After creating a Composite Application I had  modelled Business Object and Application Service in Meta data , Later I had generated a EJBimplementation. I had need to change the code in the Ejb Module But there are lot more generated Java classes generated , Inorder to make EJB module work , Could you please let me know which Class should be used,  I used all but got Null Pointer exception when i test in the service  composer

Kindly request to guide me required with sample example in  CAF. with required changes what needs to be done inorder to implement for a sample method in CAF

Thanks

Shravan