Android实现多线程下载文件的方法

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public class ThreadDownloadDemo extends Activity { 
  private TextView downloadurl; 
  private EditText downloadnum; 
  private Button downloadbutton; 
  private ProgressBar downloadProgressBar; 
  private TextView downloadinfo; 
  private int downloadedSize = 0; 
  private int fileSize = 0; 
  private long downloadtime; 
  @Override 
  public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.threaddemo); 
    downloadurl = (TextView) findViewById(R.id.downloadurl); 
    downloadurl.setText("http://file16.top100.cn/201105110911/AA5CC27CBE34DEB50A194581D1300881/Special_323149/%E8%8D%B7%E5%A1%98%E6%9C%88%E8%89%B2.mp3"); 
    downloadnum = (EditText) findViewById(R.id.downloadnum); 
    downloadinfo = (TextView) findViewById(R.id.downloadinfo); 
    downloadbutton = (Button) findViewById(R.id.downloadbutton); 
    downloadProgressBar = (ProgressBar) findViewById(R.id.downloadProgressBar); 
    downloadProgressBar.setVisibility(View.VISIBLE); 
    downloadProgressBar.setMax(100); 
    downloadProgressBar.setProgress(0); 
    downloadbutton.setOnClickListener(new OnClickListener() { 
      public void onClick(View v) { 
        download(); 
        downloadtime = SystemClock.currentThreadTimeMillis(); 
      } 
    }); 
  } 
  private void download() { 
    // 获取SD卡目录  
    String dowloadDir = Environment.getExternalStorageDirectory() 
        + "/threaddemodownload/"; 
    File file = new File(dowloadDir); 
    //创建下载目录  
    if (!file.exists()) { 
      file.mkdirs(); 
    } 
    //读取下载线程数，如果为空，则单线程下载  
    int downloadTN = Integer.valueOf("".equals(downloadnum.getText() 
        .toString()) &＃63; "1" : downloadnum.getText().toString()); 
    String fileName = "hetang.mp3"; 
    //开始下载前把下载按钮设置为不可用  
    downloadbutton.setClickable(false); 
    //进度条设为0  
    downloadProgressBar.setProgress(0); 
    //启动文件下载线程  
    new downloadTask("http://file16.top100.cn/201105110911/AA5CC27CBE34DEB50A194581D1300881/Special_323149/%E8%8D%B7%E5%A1%98%E6%9C%88%E8%89%B2.mp3", Integer 
        .valueOf(downloadTN), dowloadDir + fileName).start(); 
  } 
  Handler handler = new Handler() { 
    @Override 
    public void handleMessage(Message msg) { 
      //当收到更新视图消息时，计算已完成下载百分比，同时更新进度条信息  
      int progress = (Double.valueOf((downloadedSize * 1.0 / fileSize * 100))).intValue(); 
      if (progress == 100) { 
        downloadbutton.setClickable(true); 
        downloadinfo.setText("下载完成！"); 
        Dialog mdialog = new AlertDialog.Builder(ThreadDownloadDemo.this) 
          .setTitle("提示信息") 
          .setMessage("下载完成，总用时为:"+(SystemClock.currentThreadTimeMillis()-downloadtime)+"毫秒") 
          .setNegativeButton("确定", new DialogInterface.OnClickListener(){ 
            @Override 
            public void onClick(DialogInterface dialog, int which) { 
              dialog.dismiss(); 
            } 
          }) 
          .create(); 
        mdialog.show(); 
      } else { 
        downloadinfo.setText("当前进度:" + progress + "%"); 
      } 
      downloadProgressBar.setProgress(progress); 
    } 
  }; 
  public class downloadTask extends Thread { 
    private int blockSize, downloadSizeMore; 
    private int threadNum = 5; 
    String urlStr, threadNo, fileName; 
    public downloadTask(String urlStr, int threadNum, String fileName) { 
      this.urlStr = urlStr; 
      this.threadNum = threadNum; 
      this.fileName = fileName; 
    } 
    @Override 
    public void run() { 
      FileDownloadThread[] fds = new FileDownloadThread[threadNum]; 
      try { 
        URL url = new URL(urlStr); 
        URLConnection cOnn= url.openConnection(); 
        //防止返回-1  
        InputStream in = conn.getInputStream(); 
        //获取下载文件的总大小  
        fileSize = conn.getContentLength(); 
        Log.i("bb", "======================fileSize:"+fileSize); 
        //计算每个线程要下载的数据量  
        blockSize = fileSize / threadNum; 
        // 解决整除后百分比计算误差  
        downloadSizeMore = (fileSize % threadNum); 
        File file = new File(fileName); 
        for (int i = 0; i 

public class FileDownloadThread extends Thread{ 
  private static final int BUFFER_SIZE=1024; 
  private URL url; 
  private File file; 
  private int startPosition; 
  private int endPosition; 
  private int curPosition; 
  //标识当前线程是否下载完成  
  private boolean finished=false; 
  private int downloadSize=0; 
  public FileDownloadThread(URL url,File file,int startPosition,int endPosition){ 
    this.url=url; 
    this.file=file; 
    this.startPosition=startPosition; 
    this.curPosition=startPosition; 
    this.endPosition=endPosition; 
  } 
  @Override 
  public void run() { 
    BufferedInputStream bis = null; 
    RandomAccessFile fos = null;                         
    byte[] buf = new byte[BUFFER_SIZE]; 
    URLConnection con = null; 
    try { 
      con = url.openConnection(); 
      con.setAllowUserInteraction(true); 
      //设置当前线程下载的起止点  
      con.setRequestProperty("Range", "bytes=" + startPosition + "-" + endPosition); 
      Log.i("bb", Thread.currentThread().getName()+" bytes=" + startPosition + "-" + endPosition); 
      //使用java中的RandomAccessFile 对文件进行随机读写操作  
      fos = new RandomAccessFile(file, "rw"); 
      //设置写文件的起始位置  
      fos.seek(startPosition); 
      bis = new BufferedInputStream(con.getInputStream());  
      //开始循环以流的形式读写文件  
      while (curPosition  endPosition) { 
          downloadSize+=len - (curPosition - endPosition) + 1; 
        } else { 
          downloadSize+=len; 
        } 
      } 
      //下载完成设为true  
      this.finished = true; 
      bis.close(); 
      fos.close(); 
    } catch (IOException e) { 
      e.printStackTrace(); 
    } 
  } 
  public boolean isFinished(){ 
    return finished; 
  } 
  public int getDownloadSize() { 
    return downloadSize; 
  } 
} 
public class FileDownloadThread extends Thread{
private static final int BUFFER_SIZE=1024;
private URL url;
private File file;
private int startPosition;
private int endPosition;
private int curPosition;//标识当前线程是否下载完成
private boolean finished=false;
private int downloadSize=0;
public FileDownloadThread(URL url,File file,int startPosition,int endPosition){
this.url=url;
this.file=file;
this.startPosition=startPosition;
this.curPosition=startPosition;
this.endPosition=endPosition;
}
@Overridepublic void run() {
BufferedInputStream bis = null;
RandomAccessFile fos = null;
byte[] buf = new byte[BUFFER_SIZE];
URLConnection con = null;
try {
con = url.openConnection();
con.setAllowUserInteraction(true);
//设置当前线程下载的起止点
con.setRequestProperty("Range", "bytes=" + startPosition + "-" + endPosition);
Log.i("bb", Thread.currentThread().getName()+" bytes=" + startPosition + "-" + endPosition);
//使用java中的RandomAccessFile 对文件进行随机读写操作
fos = new RandomAccessFile(file, "rw");
//设置写文件的起始位置
fos.seek(startPosition);
bis = new BufferedInputStream(con.getInputStream());
//开始循环以流的形式读写文件
while (curPosition  endPosition) {
downloadSize+=len - (curPosition - endPosition) + 1;
} else {
downloadSize+=len;
}
}
//下载完成设为true
this.finished = true;
bis.close();
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public boolean isFinished(){return finished;}
public int getDownloadSize() {return downloadSize;}
}