Android 多线程下载

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