[ Java 代碼範本 ] SwingWorker Example

來源自 這裡
Preface :
當我們開發 Swing 程式需要執行需耗時的工作時, 可以使用 worker thread (或稱為 background threads). 而這樣的 worker thread 可以使用類別 javax.swing.SwingWorker 來完成. 它是抽象類別, 要使用時可以繼承該類別, 並實作方法 doInBackground(), 並在裡面執行耗時工作.

Demo Code:
下面的範例代碼會建立一個 UI 如下:


點擊按鈕 "Start" 將會建立 NumberWorker 的物件, 它實作 javax.swing.SwingWorker, 接著會執行你實作方法 doInBackground() 的代碼, 而當背景程式正在執行時你可以任意移動該 UI, 甚至可以在 TextField 上面輸入字串; 而在你從該方法透出後, 方法 done() 會被執行:


而在背景程式 done() 方法中, 會將取得的 random number 設回原來 UI 的 TextField 並完成背景工作.


當你在點擊按鈕 "Start" 後, 按鈕 "Cancel" 將會被 enable. 當你點擊 "Cancel" 按鈕, 在 "Start" 按鈕點擊後建立的 NumberWorker 的物件上的方法 cancel(true) (繼承來自 SwingWorker 上面方法)將會被執行, 並同時終止正在背景執行的工作.

Implementation:

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1. package swing.demo;  
2.   
3. import java.awt.BorderLayout;  
4. import java.awt.Dimension;  
5. import java.awt.FlowLayout;  
6. import java.awt.GridLayout;  
7. import java.awt.event.ActionEvent;  
8. import java.awt.event.ActionListener;  
9. import java.util.Random;  
10.   
11. import javax.swing.ImageIcon;  
12. import javax.swing.JButton;  
13. import javax.swing.JFrame;  
14. import javax.swing.JLabel;  
15. import javax.swing.JPanel;  
16. import javax.swing.JTextField;  
17. import javax.swing.SwingUtilities;  
18. import javax.swing.SwingWorker;  
19. import javax.swing.WindowConstants;  
20.   
21.   
22. public class LuckyNumber extends JFrame implements ActionListener{  
23.     private static final long serialVersionUID = 4276832367310733568L;  
24.     private JLabel label;  
25.     private JButton cancel;  
26.     private JButton start;  
27.     private SwingWorker worker;  
28.     private JTextField textField;  
29.   
30.     public LuckyNumber() {  
31.         JPanel panel = new JPanel();  
32.         panel.setLayout(new GridLayout(2, 1));  
33.   
34.         JPanel buttons = new JPanel(new FlowLayout());  
35.         start = new JButton("Start");  
36.         start.addActionListener(this);  
37.         start.setDefaultCapable(true);  
38.         buttons.add(start);  
39.         cancel = new JButton("Cancel");  
40.         cancel.setEnabled(false);  
41.         cancel.addActionListener(this);  
42.         buttons.add(cancel);  
43.         panel.add(buttons);  
44.   
45.         ImageIcon image = new ImageIcon(getClass().getClassLoader().getResource("swing/demo/images/spinner.gif"));        
46.   
47.         label = new JLabel(image);  
48.         JPanel answer = new JPanel(new GridLayout(1, 2));  
49.         textField = new JTextField("");  
50.         answer.add(textField);  
51.         answer.add(label);  
52.         label.setVisible(false);  
53.         panel.add(answer);  
54.   
55.         setTitle("Lucky number generator");  
56.         setPreferredSize(new Dimension(300, 100));  
57.         getContentPane().setLayout(new BorderLayout());  
58.         getContentPane().add(panel);  
59.   
60.     }  
61.   
62.     public static void main(String[] args) {  
63.         SwingUtilities.invokeLater(new Runnable() {  
64.             public void run() {  
65.                 LuckyNumber luckyNumber = new LuckyNumber();  
66.                 luckyNumber.pack();  
67.                 luckyNumber.setVisible(true);  
68.                 luckyNumber.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);  
69.             }  
70.         });  
71.     }  
72.   
73.     public void actionPerformed(ActionEvent e) {  
74.         if (e.getSource() == start) {  
75.             start.setEnabled(false);  
76.             textField.setText("");  
77.             worker = new NumberWorker();  
78.             worker.execute();  
79.             label.setVisible(true);  
80.             cancel.setEnabled(true);  
81.         } else if (e.getSource() == cancel) {  
82.             cancel();  
83.         }  
84.   
85.     }  
86.   
87.     @Override  
88.     public void dispose() {  
89.         cancel();  
90.         super.dispose();  
91.     }  
92.   
93.     private void cancel() {  
94.         start.setEnabled(true);  
95.         label.setVisible(false);  
96.         cancel.setEnabled(false);  
97.         if (worker != null) {  
98.             worker.cancel(true);  
99.             worker = null;  
100.         }  
101.   
102.     }  
103.   
104.     private class NumberWorker extends SwingWorker {  
105.   
106.         private Random r = new Random();  
107.   
108.         @Override  
109.         protected String doInBackground() throws Exception {  
110.             long s = System.currentTimeMillis();  
111.             while (System.currentTimeMillis() - s < 5000 && !Thread.currentThread().isInterrupted()) {  
112.                 r.nextInt();  
113.             }  
114.             return String.valueOf(r.nextInt(10) + 1);  
115.         }  
116.   
117.         @Override  
118.         protected void done() {  
119.             try {  
120.                 textField.setText(get());  
121.                 LuckyNumber.this.worker = null;  
122.                 LuckyNumber.this.cancel();  
123.             } catch (Exception ignore) {  
124.             }  
125.         }  
126.     }  
127. }  

Supplement:
* The Java Tutorial > Worker Threads and SwingWorker

When a Swing program needs to execute a long-running task, it usually uses one of the worker threads, also known as the background threads. Each task running on a worker thread is represented by an instance of javax.swing.SwingWorker. SwingWorker itself is an abstract class; you must define a subclass in order to create a SwingWorker object; anonymous inner classes are often useful for creating very simple SwingWorker objects.