EJB with transactional state

Problem: EJBean, like any POJO, can have fields. We want the changes made to the fields to be rolled back if a transaction is rolled back.

Let us consider the following scenario:

1. Client starts transaction
2. Client invokes EJB and propagates transaction
3. Assume that EJBean have field int number initially equals 0, method invoked by client sets the field number to 1
4. Client rollbacks transaction
5. It turns out that value of field number is not rolled back, the value remains 1

EJB supports global transactions but they are not transactional. I.e. they can propagate transaction to Managed Resources, for instance a database connection, but the state of EJBean does not participate in a transaction, like in the above scenario.

To make a state of EJB transactional, we must do it manually, i.e. we must provide a mechanism that restores state in a case of rollback. This can be achieved by transaction listeners. But only possible type of EJB that support such listeners is Stateful Session Bean.

@Stateful
public class TUBean {
   private TUState state;
   private TUState rollbackState;

   @PostConstruct
   private void init(){
      state = new TUState();
   }

   //business methods

   @AfterBegin
   private void afterBegin(){
      rollbackState = state.clone();
   }

   @AfterCompletion
   private void afterCompletion(boolean committed){
      if ( ! committed )
         state = rollbackState;
      rollbackState = null;
   }
}

The class TUState encapsulates whole transactional state. The state is rather simple, like POJO, without database connections. For convenience we assume that the method clone is well implemented.

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• ejb
• stateful
• transaction
• transactional