一、問題描述

當我們在網絡上加載一些圖像時，限于連接寬帶和網絡負載，下載可能需要一些時間，所以在等待圖像加載的時候，就應該顯示一些東西。我們也不希望在等待圖像時，整個應用程序被掛起。一旦圖像加載完成，剛才顯示的東西就應該消失，圖像顯示出來。

二、類圖

三、實現代碼

1.ImageComponent

class ImageComponent extends JComponent {private Icon icon;public ImageComponent(Icon icon) {this.icon = icon;}public void setIcon(Icon icon) {this.icon = icon;}public void paintComponent(Graphics g) {super.paintComponent(g);int w = icon.getIconWidth();int h = icon.getIconHeight();int x = (800 - w)/2;int y = (600 - h)/2;icon.paintIcon(this, g, x, y);} }
2.代理類ImageProxy

class ImageProxy implements Icon {ImageIcon imageIcon;URL imageURL;Thread retrievalThread;boolean retrieving = false;public ImageProxy(URL url) { imageURL = url; }public int getIconWidth() {if (imageIcon != null) {return imageIcon.getIconWidth();} else {return 800;}}public int getIconHeight() {if (imageIcon != null) {return imageIcon.getIconHeight();} else {return 600;}}public void paintIcon(final Component c, Graphics g, int x, int y) {if (imageIcon != null) {imageIcon.paintIcon(c, g, x, y);} else {g.drawString("Loading CD cover, please wait...", x+300, y+190);if (!retrieving) {retrieving = true;retrievalThread = new Thread(new Runnable() {public void run() {try {imageIcon = new ImageIcon(imageURL, "CD Cover");c.repaint();} catch (Exception e) {e.printStackTrace();}}});retrievalThread.start();}}} }
3.測試

public class ImageProxyTestDrive {ImageComponent imageComponent;JFrame frame = new JFrame("CD Cover Viewer");JMenuBar menuBar;JMenu menu;Hashtable cds = new Hashtable();public static void main(String[] args) throws Exception{ImageProxyTestDrive testDrive = new ImageProxyTestDrive();}public ImageProxyTestDrive() throws Exception{cds.put("Ambient: Music for Airports","http://images.amazon.com/images/P/B000003S2K.01.LZZZZZZZ.jpg");cds.put("Buddha Bar","http://images.amazon.com/images/P/B00009XBYK.01.LZZZZZZZ.jpg");cds.put("Ima","http://images.amazon.com/images/P/B000005IRM.01.LZZZZZZZ.jpg");cds.put("Karma","http://images.amazon.com/images/P/B000005DCB.01.LZZZZZZZ.gif");cds.put("MCMXC A.D.","http://images.amazon.com/images/P/B000002URV.01.LZZZZZZZ.jpg");cds.put("Northern Exposure","http://images.amazon.com/images/P/B000003SFN.01.LZZZZZZZ.jpg");cds.put("Selected Ambient Works, Vol. 2","http://images.amazon.com/images/P/B000002MNZ.01.LZZZZZZZ.jpg");URL initialURL = new URL((String) cds.get("Selected Ambient Works, Vol. 2"));menuBar = new JMenuBar();menu = new JMenu("Favorite CDs");menuBar.add(menu);frame.setJMenuBar(menuBar);for (Enumeration e = cds.keys(); e.hasMoreElements();){String name = (String) e.nextElement();JMenuItem menuItem = new JMenuItem(name);menu.add(menuItem);menuItem.addActionListener(new ActionListener(){public void actionPerformed(ActionEvent event){imageComponent.setIcon(new ImageProxy(getCDUrl(event.getActionCommand())));frame.repaint();}});}//建立框架和菜單Icon icon = new ImageProxy(initialURL);imageComponent = new ImageComponent(icon);frame.getContentPane().add(imageComponent);frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setSize(800, 600);frame.setVisible(true);}URL getCDUrl(String name){try{return new URL((String) cds.get(name));}catch (MalformedURLException e){e.printStackTrace();return null;}} }
運行窗口：

（加載圖片時顯示"Loading CD cover, please wait..."，反應太快，就不截圖了）

轉載請注明出處：http://blog.csdn.net/jialinqiang/article/details/8974694

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