code: public static Object requiredSingleResult(Collection results) throws DatabaseException {
          int size = ((results != null) ? results.size() : 0);
          if (size == 0) {
              throw new DatabaseException("Empty result set, expected one row");
          }
          if (results.size() > 1) {
              throw new DatabaseException("Result set larger than one row");
          }
          return results.iterator().next();
      }
docs: Return a single result object from the given Collection.
  <p>Throws an exception if 0 or more than 1 element found.
  @param results the result Collection (can be <code>null</code>)
  @return the single result object