Android 多線程下載文件

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="

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        try {
            download(url);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

//進行下載的線程
class DownloadThread extends Thread {
    private URL url;
    private RandomAccessFile file;
    private long from;
    private long end;

    /**
     * @param url 下載的URL
     * @param file 下載完成之后存儲的文件
     * @param from 當前線程對應文件的起始位置
     * @param end 當前線程對應文件的結束位置
     */
    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();

            //設置請求的起始和結束位置。
            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;//每個線程要下載的字節數
    long leftLength = fileLength % THREAD_COUNT;//剩下的字節數

    RandomAccessFile file = new RandomAccessFile(SaveFile, "rw");

    System.out.println(fileLength);
    //計算每個線程請求的起始位置和結束位置。
    /*
     * 第一個線程的起始位置是0~0+packageLength(每個線程要下載的字節數)
     * 第二個線程的起始位置是endPos+1(第一個線程的packageLength+1)~endPos+1+packageLength
     * 第二個線程的起始位置是.........
     */
    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();
}


}</pre>


保存為test.mp3文件