当单击按钮从网络加载图像时，如何防止表单冻结？

Question

I want to display an image from the web to a panel in another Jframe at the click of a button but whenever I click the button first the image loads and during this time the current form potentially freezes and once the image has loaded the form is displayed with the image.. How can I avoid the situation where my form freezes since it is very irritating

My codes ::

My current class

private void btn_TrackbusActionPerformed(java.awt.event.ActionEvent evt) {                                             
        try {
            sendMessage("Query,map,$,start,211,Arsenal,!");
            System.out.println(receiveMessage());
        } catch (UnknownHostException ex) {
            Logger.getLogger(client_Trackbus.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(client_Trackbus.class.getName()).log(Level.SEVERE, null, ex);
        }
        catch (Exception ex) {
            Logger.getLogger(client_Trackbus.class.getName()).log(Level.SEVERE, null, ex);
        }
        client_trackedbus nextform=new client_trackedbus(planform,connection,packet_receive,packet_send);
        this.setVisible(false);
        this.dispose();
        nextform.setVisible(true);
        // TODO add your handling code here:
    }                                            

My next class that displays the image

public class client_trackedbus extends javax.swing.JFrame {
    client_planform planform=null;
    DatagramSocket connection=null;
    DatagramPacket packet_receive=null;
    DatagramPacket packet_send=null;
    JLabel label=null;
    /** Creates new form client_trackedbus */
    public client_trackedbus(client_planform planform,DatagramSocket 
        connection,DatagramPacket packet_receive,DatagramPacket packet_send) {
        initComponents();
        this.planform=planform;
        this.connection=connection;
        this.packet_receive=packet_receive;
        this.packet_send=packet_send;
        try {
            displayMap("http://www.huddletogether.com/projects/lightbox2/images/image-2.jpg", jPanel1, new JLabel());
        } catch (MalformedURLException ex) {
            Logger.getLogger(client_trackedbus.class.getName()).log(Level.SEVERE, null, ex);
        }

    }


    private void displayMap(String url,JPanel panel,JLabel label) throws MalformedURLException{
        URL imageurl=new URL(url);
        Image image=(Toolkit.getDefaultToolkit().createImage(imageurl));
        ImageIcon icon = new ImageIcon(image);
        label.setIcon(icon);
        panel.add(label);
       // System.out.println(panel.getSize().width);
        this.getContentPane().add(panel);
    }


    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();
        jLabel1 = new javax.swing.JLabel();
        btn_Exit = new javax.swing.JButton();
        btn_Plan = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Public Transport Journey Planner");

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 368, Short.MAX_VALUE)
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 172, Short.MAX_VALUE)
        );

        jLabel1.setFont(new java.awt.Font("Arial", 1, 18));
        jLabel1.setText("Your tracked bus");

        btn_Exit.setText("Exit");
        btn_Exit.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn_ExitActionPerformed(evt);
            }
        });

        btn_Plan.setText("Plan journey");
        btn_Plan.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btn_PlanActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addGap(104, 104, 104)
                        .addComponent(jLabel1))
                    .addGroup(layout.createSequentialGroup()
                        .addContainerGap()
                        .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(65, 65, 65)
                        .addComponent(btn_Plan)
                        .addGap(65, 65, 65)
                        .addComponent(btn_Exit, javax.swing.GroupLayout.PREFERRED_SIZE, 87, javax.swing.GroupLayout.PREFERRED_SIZE)))
                .addContainerGap(20, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(35, 35, 35)
                .addComponent(jLabel1)
                .addGap(18, 18, 18)
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(btn_Exit)
                    .addComponent(btn_Plan))
                .addContainerGap(12, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                        

    private void btn_ExitActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        Exitform();
    }                                        

    private void btn_PlanActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        this.setVisible(false);
        this.dispose();
         this.planform.setVisible(true);
    }                                        


    private void Exitform(){
        this.setVisible(false);
        this.dispose();

    }
    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
               // new client_trackedbus().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton btn_Exit;
    private javax.swing.JButton btn_Plan;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JPanel jPanel1;
    // End of variables declaration                   

}

Answer 1

you definitely need to use swingworker as trashgod suggested. to make this connection clear, heres an example i strongly suggest you try out. check "A More Complex Image Icon Example" in this link, and understand the code. it perfectly solves your problem. http://download.oracle.com/javase/tutorial/uiswing/components/icon.html

in particular, pay attention to this bit of code:

 public IconDemoApp() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setTitle("Icon Demo: Please Select an Image");

    // A label for displaying the pictures
    photographLabel.setVerticalTextPosition(JLabel.BOTTOM);
    photographLabel.setHorizontalTextPosition(JLabel.CENTER);
    photographLabel.setHorizontalAlignment(JLabel.CENTER);
    photographLabel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

    // We add two glue components. Later in process() we will add thumbnail buttons
    // to the toolbar inbetween thease glue compoents. This will center the
    // buttons in the toolbar.
    buttonBar.add(Box.createGlue());
    buttonBar.add(Box.createGlue());

    add(buttonBar, BorderLayout.SOUTH);
    add(photographLabel, BorderLayout.CENTER);

    setSize(400, 300);

    // this centers the frame on the screen
    setLocationRelativeTo(null);

    // start the image loading SwingWorker in a background thread
    loadimages.execute();
}

you can see in this constructor how event dispatch is occuring separately from loadimages.execute(), which uses the swingworker to load images in the background. i'll be happy to clarify any doubts.

Answer 2

The form will freeze as soon as btn_TrackbusActionPerformed() is called. The form will not unfreeze until btn_TrackbusActionPerformed() returns.

The solution is to have btn_TrackbusActionPerformed() start a thread and run all the code that is currently in btn_TrackbusActionPerformed() asynchronously on the new thread.

Note that you will have thread safety issues when calling the Swing API on the new thread.