Listing 1

 
/**
* Singleton exists on a per JVM basis and returns a new, unique ID
* to the caller.
*/
public class Singleton {
    private long max = 0;
    private long currentID = 0;
    private static Singleton singleton = new Singleton();
    private UniqueID uniqueIDEJB;
    /**
    * Accessor to get handle to singleton object.
    */
    public Singleton instance() {
 return singleton;
    }
    /**
    * Cannot instantiate.  Must use instance() method to get a handle to the object.
    */
    private Singleton() {
 // GET HANDLE TO UNIQUEID EJB
    }

    /**
    * Returns a unique ID to the caller. This is synchronized to prevent
    * multiple callers from getting the same ID back if they called getNextID() at the
    * same time.
    *
    *
    * @return long   next ID
    */
    public synchronized long getNextID() throws Exception{
        currentID++;
 if (currentID > max) {
     try{
  IDSet set = uniqueIdEJB.getNextIDSet();
 
  // reset current id
  currentID = set.getMin();
  max = set.getMax();
      }
     catch(Exception ex) {
  ex.printStackTrace();
  throw ex;
     }
       }
 return currentID;
    }