Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

17.4 A Query Viewer That Uses Object Serialization and HTTP Tunneling

445

Listing 17.4 ShowQueries.java (continued)

    clearButton.setFont(buttonFont);

    clearButton.addActionListener(this);

    buttonPanel.add(clearButton);

    add(buttonPanel, BorderLayout.SOUTH);

    currentPage = getCodeBase();

    // Request a set of sample queries. They

    // are loaded in a background thread, and

    // the applet checks to see if they have finished

    // loading before trying to extract the strings.

    currentQueries = new QueryCollection(address, currentPage);

    nextQueries = new QueryCollection(address, currentPage);

  }

  /** If you press the "Start" button, the system

   *  starts a background thread that displays

   *  the queries in the TextArea. Pressing "Stop"

   *  halts the process, and "Clear" empties the

   *  TextArea.

   */

  public void actionPerformed(ActionEvent event) {

    if (event.getSource() == startButton) {

      if (!isRunning) {

        Thread queryDisplayer = new Thread(this);

        isRunning = true;

        queryArea.setText("");

        queryDisplayer.start();

        showStatus("Started display thread...");

      } else {

        showStatus("Display thread already running...");

      }

    } else if (event.getSource() == stopButton) {

      isRunning = false;

      showStatus("Stopped display thread...");

    } else if (event.getSource() == clearButton) {

      queryArea.setText("");

    }

  }

  /** The background thread takes the currentQueries

   *  object and every half second places one of the queries

   *  the object holds into the bottom of the TextArea. When

   *  all of the queries have been shown, the thread copies

   *  the value of the nextQueries object into

   *  currentQueries, sends a new request to the server

   *  in order to repopulate nextQueries, and repeats

   *  the process.

   */

Home page for this book: www.coreservlets.com; Home page for sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.