多线程下载器

多线程下载器

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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( "网络资源的多线程下载：" );      private final JLabel label2 = new JLabel( "网络资源的网址：" );      JButton StartButton = new JButton( "点击开始下载" );      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 , "请输入资源地址" );              }              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 );          }      }        /**       * 下载网络资源       * */      public void download(String url, String dest, int threadNum)              throws Exception{          URL downURL = new URL(url);          // 打开网络连接          HttpURLConnection conn = (HttpURLConnection) downURL.openConnection();          // 创建文件长度的变量          long fileLength = - 1 ;          // 获得连接状态标记代码          int stateFlagCode = conn.getResponseCode();          if (stateFlagCode == 200 ){              // 网络连接正常              fileLength = conn.getContentLength();              // 取笑网络连接              conn.disconnect();          }          if (fileLength > 0 ){              // 计算每个线程的字节数              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   /**   * 用于实现网络资源的下载   * */ class DownMulltiThread implements Runnable{        public DownMulltiThread(){        }        /**       * @param sUrl       *            网络资源位置       * @param desFile       *            需要写入的文件对象       * @param startPos       *            写入的开始位置       * @param endPos       *            写入文件的结束位置       * */      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();          }      } }