多線程下載器

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package net;   import java.awt.FlowLayout; import java.awt.Font; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.io.BufferedInputStream; import java.io.File; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL; import java.net.URLConnection;   import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JOptionPane; import javax.swing.JPanel; import javax.swing.JTextField;   public class DownMultiThreadFrame extends JFrame implements ActionListener{     public DownMultiThreadFrame(){         panel.setLayout(new FlowLayout());         label1.setFont(new Font("雅黑", Font.BOLD, 15));         panel.add(label1);         panel.add(label2);         panel.add(urlField);         panel.add(StartButton);         panel.add(resetButton);         panel.add(exitButton);         setContentPane(panel);         StartButton.addActionListener(this);         resetButton.addActionListener(this);         exitButton.addActionListener(this);         setSize(400, 400);         setVisible(true);         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);     }       public static void main(String[] args){         new DownMultiThreadFrame();       }       private final JPanel panel = new JPanel();     private final JLabel label1 = new JLabel("網絡資源的多線程下載：");     private final JLabel label2 = new JLabel("網絡資源的網址：");     JButton StartButton = new JButton("點擊開始下載");     JButton resetButton = new JButton("清空");     JButton exitButton = new JButton("退出");     JTextField urlField = new JTextField(20);       @Override     public void actionPerformed(ActionEvent e){         if(e.getSource() == StartButton){             if("".equals(urlField.getText())){                 JOptionPane.showMessageDialog(this, "請輸入資源地址");             }             String url = urlField.getText();             int pos = url.lastIndexOf("/");             String fileName = url.substring(pos + 1);             try{                 download(url, "d:\\" + fileName, 2);             }catch(Exception e1){                 e1.printStackTrace();             }         }else if(e.getSource() == resetButton){             urlField.setText("");         }else{             System.exit(0);         }     }       /**      * 下載網絡資源      * */     public void download(String url, String dest, int threadNum)             throws Exception{         URL downURL = new URL(url);         // 打開網絡連接         HttpURLConnection conn = (HttpURLConnection) downURL.openConnection();         // 創建文件長度的變量         long fileLength = -1;         // 獲得連接狀態標記代碼         int stateFlagCode = conn.getResponseCode();         if(stateFlagCode == 200){             // 網絡連接正常             fileLength = conn.getContentLength();             // 取笑網絡連接             conn.disconnect();         }         if(fileLength > 0){             // 計算每個線程的字節數             long byteCounts = fileLength / threadNum + 1;             File file = new File(dest);             int i = 0;             while(i < threadNum){                 long startPosition = byteCounts * i;                 long endPosition = byteCounts * (i + 1);                 if(i == threadNum - 1){                     DownMulltiThread fileThread = new DownMulltiThread(url,                             file, startPosition, 0);                     new Thread(fileThread).start();                 }else{                     DownMulltiThread fileThread = new DownMulltiThread(url,                             file, startPosition, endPosition);                     new Thread(fileThread).start();                 }                 i++;             }         }     }   }// end class   /**  * 用於實現網絡資源的下載  * */ class DownMulltiThread implements Runnable{       public DownMulltiThread(){       }       /**      * @param sUrl      *            網絡資源位置      * @param desFile      *            需要寫入的文件對象      * @param startPos      *            寫入的開始位置      * @param endPos      *            寫入文件的結束位置      * */     public DownMulltiThread(String sUrl, File desFile, long startPos,             long endPos){         this.desFile = desFile;         this.sUrl = sUrl;         this.startPos = startPos;         this.endPos = endPos;     }       private String sUrl = "";     private File desFile;     private long startPos;     private long endPos;       @Override     public void run(){         RandomAccessFile out;         try{             out = new RandomAccessFile(desFile, "rw");             out.seek(startPos);             URL url = new URL(sUrl);             URLConnection urlcon = url.openConnection();             urlcon.connect();             InputStream in = urlcon.getInputStream();             BufferedInputStream buf = new BufferedInputStream(in);             byte[] bytes = new byte[1024];             int len = buf.read(bytes);             while(len != -1){                 out.write(bytes, 0, len);                 len = buf.read(bytes);             }           }catch(FileNotFoundException e){             e.printStackTrace();         }catch(IOException e){             e.printStackTrace();         }     } }