code: @Override
      public void close() {
          namedParamSqlCache.clear();
          namedParamIndexPropCache.clear();
          clearStatementCache();
          if (useConnection != null) {
              try {
                  useConnection.close();
              } catch (SQLException e) {
                  LOG.finest("Caught exception closing connection: " + e.getMessage());
              }
          }
      }
docs: If this SQL object was created with a Connection then this method closes
  the connection. If this SQL object was created from a DataSource then
  this method only frees any cached objects (statements in particular).