code: public void returnConnection(DataConnection connection) {
          if (connection.isUsable()) {
              connection.setLastUsage(new Date());
              availableConnections.add(connection);
          }
          else {
              connection.close();
          }
  
          usedConnections.remove(connection);
      }
docs: Returns a connection to the pool of available and free data connections to this server.
  @param connection data connection to this server