Android 多线程下载文件

package my.Thread;    import java.io.BufferedInputStream;  import java.io.RandomAccessFile;  import java.net.HttpURLConnection;  import java.net.URL;  import java.net.URLConnection;  import java.util.concurrent.CountDownLatch;      import android.app.Activity;  import android.os.Bundle;  import android.os.Environment;  import android.view.View;  import android.view.View.OnClickListener;  import android.widget.Button;  import android.widget.TextView;    public class ManyThreadActivity extends Activity {      /** Called when the activity is first created. */    private Button button;    private TextView textView;    private static final int THREAD_COUNT = 4;    private CountDownLatch latch = new CountDownLatch(THREAD_COUNT);    private long completeLength = 0;    private long fileLength;     public static String SaveFile=Environment.getExternalStorageDirectory()+"/DownFile/"+"test.Mp3";       public static final String url="http://210.30.12.33:8080/mp3/Beyond.mp3";      @Override      public void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.main);          button=(Button)findViewById(R.id.button1);          textView=(TextView) findViewById(R.id.editText1);          textView.setText(url);          button.setOnClickListener(new MyListener());      }      class MyListener implements OnClickListener{      @Override    public void onClick(View v) {     // TODO Auto-generated method stub     try {      download(url);     } catch (Exception e) {      // TODO Auto-generated catch block      e.printStackTrace();     }    }             }        //进行下载的线程      class DownloadThread extends Thread {          private URL url;          private RandomAccessFile file;          private long from;          private long end;            /**           * @param url 下载的URL           * @param file 下载完成之后存储的文件           * @param from 当前线程对应文件的起始位置           * @param end 当前线程对应文件的结束位置           */          DownloadThread(URL url, RandomAccessFile file, long from, long end) {              this.url = url;              this.file = file;              this.from = from;              this.end = end;          }            public void run() {              try {                  long pos = from;                  byte[] buf = new byte[1024*8];                    HttpURLConnection cn = (HttpURLConnection) url.openConnection();                                   //设置请求的起始和结束位置。                  cn.setRequestProperty("Range", "bytes=" + from + "-" + end);                    BufferedInputStream bis = new BufferedInputStream(cn.getInputStream());                  int len;                  while ((len = bis.read(buf)) > 0) {                      synchronized (file) {                          file.seek(pos);                          file.write(buf, 0, len);                      }                      pos += len;                      completeLength += len;                      System.out.println(completeLength * 100 / fileLength + "%");                  }                  cn.disconnect();              } catch (Exception e) {                  e.printStackTrace();              }              latch.countDown();          }      }        public void download(String address) throws Exception {          URL url = new URL(address);          URLConnection cn = url.openConnection();          fileLength = cn.getContentLength();          long packageLength = fileLength / THREAD_COUNT;//每个线程要下载的字节数          long leftLength = fileLength % THREAD_COUNT;//剩下的字节数                   RandomAccessFile file = new RandomAccessFile(SaveFile, "rw");                   System.out.println(fileLength);          //计算每个线程请求的起始位置和结束位置。          /*           * 第一个线程的起始位置是0~0+packageLength(每个线程要下载的字节数)           * 第二个线程的起始位置是endPos+1(第一个线程的packageLength+1)~endPos+1+packageLength           * 第二个线程的起始位置是.........           */          long pos = 0;          for (int i = 0; i < THREAD_COUNT; i++) {              long endPos = pos + packageLength;              new DownloadThread(url, file, pos, endPos).start();              if(leftLength > 0) {                  endPos++;                  leftLength--;              }              pos = endPos;          }          latch.await();      }    }

保存为test.mp3文件