Add state transition validation logic

The CodetableState and Transition helper classes provide the following standard validation to disallow any transition which is not explicitly specified. For example, the state transition diagram does not permit an entity instance in the closed state to transition to any other state; by default, any attempts to.suspend() an entity instance which is currently closed will result in this error being raised: Cannot transition from 'Closed' to 'Suspended'.

You can add logic (typically to perform validations and/or notifications) to the following places:

in your State objects:
- onEnter - this method is called whenever a transition occurs which attempts to enter this State;
- onLeave - this method is called whenever a transition occurs which attempts to leave this State; and
- onUnsupportedTransitionFrom - this method is called whenever an unsupported transition is attempted which attempts to transition to this State from the one specified; by default, the CodetableState helper class raises a default message, but you are free to provider your own validation/notification logic; and
in your Transition objects:
- onTransition - this method is called whenever this Transition occurs.

See the Javadoc for the State, CodetableState and Transition helper classes for more information.

For example, if you want your logic to send an email whenever your entity is closed (regardless of whether it was previously open or suspended), override the onEnter method of your CLOSED state:

Figure 1. Adding state transition validation logic

/**
       * No longer conducting business with the agency.
       */
     private final State<MYLIFECYCLEENTITYSTATEEntry> CLOSED =
       new CodetableState<MYLIFECYCLEENTITYSTATEEntry>(
      states, MYLIFECYCLEENTITYSTATEEntry.CLOSED, false, false) {

      @Override
      protected void onEnter() {
      // whenever the entity is closed, send an email
      sendClosureEmail();
      }

      };