code: public KeyTransactionCache keyTransactions(long applicationId)
      {
          KeyTransactionCache cache = keyTransactions.get(applicationId);
          if(cache == null)
              keyTransactions.put(applicationId, cache = new KeyTransactionCache(applicationId));
          return cache;
      }
docs: Returns the cache of key transactions for the given application, creating one if it doesn't exist .
  @param applicationId The id of the application for the cache of key transactions
  @return The cache of key transactions for the given application