code: protected void dispose() {
          // Terminates the server thread
          if(serverThread != null) {
              serverThread.interrupt();
              serverThread = null;
          }
  
          // Stops each connection and clears them
          synchronized(connections) {
              for(FTPConnection con : connections) {
                  try {
                      con.stop(true);
                  } catch(Exception ex) {
                      ex.printStackTrace();
                  }
              }
              connections.clear();
          }
      }
docs: Starts disposing server resources.
  
  For a complete cleanup, use {@link #close()} instead