断点续传工具类

1 ：DownloadTask类：
   
package com.youteach.util;
import java.io.File;
import java.net.URL;
import java.net.URLConnection;
import android.os.Message;
import android.util.Log;
public class DownloadTask extends Thread {
private int blockSize, downloadSizeMore;
private int threadNum = 5;
String urlStr, threadNo, fileName;
private int fileSize, downloadedSize;
private OnDownLoadCompetionListener listener;
/**
  * @param urlStr
  *            下载的URL
  * @param threadNum
  *            下载的线程数
  * @param fileName
  *            文件名
  */
public DownloadTask(String urlStr, int threadNum, String fileName,
   OnDownLoadCompetionListener listener) {
  this.urlStr = urlStr;
  this.threadNum = threadNum;
  this.fileName = fileName;
  this.listener = listener;
  Log.i("DownloadTask-->urlStr", urlStr + "");
  Log.i("DownloadTask-->fileName", fileName + "");
}
@Override
public void run() {
  FileDownloadThread[] fds = new FileDownloadThread[threadNum];
  try {
   URL url = new URL(urlStr);
   URLConnection conn = url.openConnection();
   // 获取下载文件的总大小
   fileSize = conn.getContentLength();
   // 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 < threadNum; i++) {
    // 启动线程，分别下载自己需要下载的部分
    FileDownloadThread fdt = new FileDownloadThread(url, file, i
      * blockSize, (i + 1) * blockSize - 1);
    fdt.setName("Thread" + i);
    fdt.start();
    fds[i] = fdt;
   }
   boolean finished = false;
   while (!finished) {
    // 先把整除的余数搞定
    downloadedSize = downloadSizeMore;
    finished = true;
    for (int i = 0; i < fds.length; i++) {
     downloadedSize += fds[i].getDownloadSize();
     if (!fds[i].isFinished()) {
      finished = false;
     }
    }
    Log.i("DownloadTask-->downloadedSize", downloadedSize + "");
    Log.i("DownloadTask-->fileSize", fileSize + "");
    // 更新UI
    if (listener != null) {
     listener.onProgress(downloadedSize, fileSize);
    }
    // 休息1秒后再读取下载进度
    this.sleep(1000);
   }
   // 下载完成
   if (finished) {
    if (listener != null) {
     listener.onCompetion();
    }
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
}
}

2  下载线程类：FileDownloadThread
package com.youteach.util;
import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.URL;
import java.net.URLConnection;
/**
* @author gongchaobin
*
*     android多线程下载
*  单个下载线程
*/
public class FileDownloadThread extends Thread{
    private static final int BUFFER_SIZE=1024;
    private URL url;
    private File file;
    private int startPosition;//当前线程下载的起点
    private int endPosition;//当前线程下载的终点
    private int curPosition;
    private boolean finished=false;    //用于标识当前线程是否下载完成
    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点，终点
            con.setRequestProperty("Range", "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");
            //设置开始写文件的位置
            fos.seek(startPosition);
            bis = new BufferedInputStream(con.getInputStream()); 
            //开始循环以流的形式读写文件
            while (curPosition < endPosition) {
                int len = bis.read(buf, 0, BUFFER_SIZE);               
                if (len == -1) {
                    break;
                }
                fos.write(buf, 0, len);
                curPosition = curPosition + len;
                if (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;
    }
}

3  接口：OnDownLoadCompetionListener
package com.youteach.util;
public interface OnDownLoadCompetionListener {
public void onProgress(int progress, int total);
public void onCompetion();
}

转自：http://user.qzone.qq.com/363669440/blog/1352163034#!app=2&via=QZ.HashRefresh&pos=1352163034