public class MultiDownload {
    static int ThreadCount = ;
    static int finishedThread = ;
    //確定下載地址
    static String filename = "EditPlus.exe";
    static String path = "http://...:/"+filename;
    public static void main(String[] args) {
      //、發(fā)送get請(qǐng)求，去獲得下載文件的長(zhǎng)度
     try {
       URL url = new URL(path);
       HttpURLConnection conn = (HttpURLConnection) url.openConnection();
       conn.setRequestMethod("GET");
       conn.setConnectTimeout();
       conn.setReadTimeout();
       if (conn.getResponseCode()==) {
         //如果請(qǐng)求成功，拿到所請(qǐng)求資源文件的長(zhǎng)度
         int length = conn.getContentLength();
         //、生成一個(gè)與原文件同樣的大小的臨時(shí)文件，以免下載一半存儲(chǔ)空間不夠了
         File file = new File(filename);//演示，所以將保存的文件目錄放在工程的同目錄
         //使用RandomAccessFile 生成臨時(shí)文件，可以用指針定位文件的任意位置，
         //而且能夠?qū)崟r(shí)寫到硬件底層設(shè)備，略過(guò)緩存，這對(duì)下載文件是突然斷電等意外是有好處的
         RandomAccessFile raf = new RandomAccessFile(file, "rwd");//rwd, 實(shí)時(shí)寫到底層設(shè)備
         //設(shè)置臨時(shí)文件的大小
         raf.setLength(length);
         raf.close();
         //、計(jì)算出每個(gè)線程應(yīng)該下載多少個(gè)字節(jié)
         int size = length/ThreadCount;//如果有余數(shù)，負(fù)責(zé)最后一部分的線程負(fù)責(zé)下砸
         //開(kāi)啟多線程
         for (int threadId = ; threadId < ThreadCount; threadId++) {
           //計(jì)算每個(gè)線程下載的開(kāi)始位置和結(jié)束位置
           int startIndex = threadId*size; // 開(kāi)始 = 線程id * size
           int endIndex = (threadId+)*size - ; //結(jié)束 = （線程id + )*size - 
           //如果是最后一個(gè)線程，那么結(jié)束位置寫死為文件結(jié)束位置
           if (threadId == ThreadCount - ) {
             endIndex = length - ;
           }
           //System.out.println("線程"+threadId+"的下載區(qū)間是： "+startIndex+"----"+endIndex);
           new DownloadThread(startIndex,endIndex,threadId).start();
         }
       }
     } catch (MalformedURLException e) {
       e.printStackTrace();
     } catch (IOException e) {
       e.printStackTrace();
     }
   }
 }
 class DownloadThread extends Thread{
   private int startIndex;
   private int endIndex;
   private int threadId;
   public DownloadThread(int startIndex, int endIndex, int threadId) {
     super();
     this.startIndex = startIndex;
     this.endIndex = endIndex;
     this.threadId = threadId;
   }
    public void run() {
      //每個(gè)線程再次發(fā)送http請(qǐng)求，下載自己對(duì)應(yīng)的那部分?jǐn)?shù)據(jù)
     try {
       File progressFile = new File(threadId+".txt");
       //判斷進(jìn)度文件是否存在，如果存在，則接著斷點(diǎn)繼續(xù)下載，如果不存在，則從頭下載
       if (progressFile.exists()) {
         FileInputStream fis = new FileInputStream(progressFile);
         BufferedReader br = new BufferedReader(new InputStreamReader(fis));
         //從進(jìn)度文件中度取出上一次下載的總進(jìn)度，然后與原本的開(kāi)始進(jìn)度相加，得到新的開(kāi)始進(jìn)度
         startIndex += Integer.parseInt(br.readLine());
         fis.close();
       }
       System.out.println("線程"+threadId+"的下載區(qū)間是:"+startIndex+"----"+endIndex);
       //、每個(gè)線程發(fā)送http請(qǐng)求自己的數(shù)據(jù)
       URL url = new URL(MultiDownload.path);
       HttpURLConnection conn = (HttpURLConnection) url.openConnection();
       conn.setRequestMethod("GET");
       conn.setConnectTimeout();
       conn.setReadTimeout();
       //設(shè)置本次http請(qǐng)求所請(qǐng)求的數(shù)據(jù)的區(qū)間
       conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex);
       //請(qǐng)求部分?jǐn)?shù)據(jù)，響應(yīng)碼是
       if (conn.getResponseCode()==) {
         //此時(shí)，流里只有ThreadCount分之一的原文件數(shù)據(jù)
         InputStream is = conn.getInputStream();
         byte[] b = new byte[];
         int len = ;
         int total = ;//total 用于保存斷點(diǎn)續(xù)傳的斷點(diǎn)
         //拿到臨時(shí)文件的輸出流
         File file = new File(MultiDownload.filename);
         RandomAccessFile raf = new RandomAccessFile(file, "rwd");
         //把文件的寫入位置移動(dòng)至 startIndex
         raf.seek(startIndex);
         while ((len = is.read(b))!=-) {
           //每次讀取流里數(shù)據(jù)之后，同步把數(shù)據(jù)寫入臨時(shí)文件
           raf.write(b, , len);
           total += len;
           //System.out.println("線程" + threadId + "下載了" + total);
           //生成一個(gè)一個(gè)專門用來(lái)記錄下載進(jìn)度的臨時(shí)文件
           RandomAccessFile progressRaf = new RandomAccessFile(progressFile, "rwd");
           progressRaf.write((total+"").getBytes());
           progressRaf.close();
         }
         System.out.println("線程"+threadId+"下載完了---------------------");
         raf.close();
         //當(dāng)所有的線程下載完之后，將進(jìn)度文件刪除
         MultiDownload.finishedThread++;
         synchronized (MultiDownload.path) {//所有線程使用同一個(gè)鎖
           if (MultiDownload.finishedThread==MultiDownload.ThreadCount) {
             for (int i = ; i < MultiDownload.ThreadCount; i++) {
               File f = new File(i+".txt");
               f.delete();
             }
             MultiDownload.finishedThread=;
           }
         }
       }  
     } catch (Exception e) {
       e.printStackTrace();
     }
   }
 }

public class MainActivity extends Activity {
  static int ThreadCount = ;
  static int FinishedThread = ;
  int currentProgess;
  static String Filename = "QQPlayer.exe";
  static String Path = "http://...:/"+Filename;
  static MainActivity ma;
  static ProgressBar pb;
  static TextView tv;
  static Handler handler = new Handler(){
    public void handleMessage(android.os.Message msg){
      tv.setText((long)pb.getProgress()* /pb.getMax() +"%");
    };
  };
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ma = this;
    pb = (ProgressBar) findViewById(R.id.pb);
    tv = (TextView) findViewById(R.id.tv);
  }
  public void download(View v){
    Thread t = new Thread(){
      public void run() {
        //發(fā)送http請(qǐng)求獲取文件的長(zhǎng)度，創(chuàng)建臨時(shí)文件
        try {
          URL url= new URL(Path);
          HttpURLConnection conn = (HttpURLConnection) url.openConnection();
          conn.setRequestMethod("GET");
          conn.setConnectTimeout();
          conn.setReadTimeout();
          if (conn.getResponseCode()==) {
            int length = conn.getContentLength();
            //設(shè)置進(jìn)度條的最大值就是原文件的總長(zhǎng)度
            pb.setMax(length);
            //生成一個(gè)與原文件相同大小的臨時(shí)文件
            File file = new File(Environment.getExternalStorageDirectory(),Filename);
            RandomAccessFile raf = new RandomAccessFile(file, "rwd");
            raf.setLength(length);
            raf.close();
            //計(jì)算每個(gè)線程需要下載的數(shù)據(jù)大小
            int size = length/ThreadCount;
            //開(kāi)啟多線程
            for (int threadId = ; threadId < ThreadCount; threadId++) {
              int startIndex = threadId*size;
              int endIndex = (threadId + )*size - ;
              if (threadId==ThreadCount - ) {
                endIndex = length - ;
              }
              new DownloadThread(startIndex, endIndex, threadId).start();
            }
          }
        } catch (Exception e) {
          e.printStackTrace();
        }
      }
    };
    t.start();
  }
  class DownloadThread extends Thread{
    private int startIndex;
    private int endIndex;
    private int threadId;
    public DownloadThread(int startIndex, int endIndex, int threadId) {
      super();
      this.startIndex = startIndex;
      this.endIndex = endIndex;
      this.threadId = threadId;
    }
    public void run() {
      // 每個(gè)線程發(fā)送http請(qǐng)求自己的數(shù)據(jù)
      try{
        //先判斷是不是斷點(diǎn)續(xù)傳
        File progessFile = new File(Environment.getExternalStorageDirectory(),threadId+".txt");
        if (progessFile.exists()) {
          FileReader fr = new FileReader(progessFile);
          BufferedReader br = new BufferedReader(fr);
          int lastProgess = Integer.parseInt(br.readLine());
          startIndex += lastProgess;
          //把上次下載的進(jìn)度顯示至進(jìn)度條
          currentProgess +=lastProgess;
          pb.setProgress(currentProgess);
          //發(fā)消息，讓主線程刷新文本進(jìn)度
          handler.sendEmptyMessage();
          br.close();
          fr.close();
        }
        URL url = new URL(Path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout();
        conn.setReadTimeout();
        conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex);
        if (conn.getResponseCode()==) {
          InputStream is = conn.getInputStream();
          byte[] buffer = new byte[];
          int len = ;
          int total = ;
          File file = new File(Environment.getExternalStorageDirectory(),Filename);
          RandomAccessFile raf = new RandomAccessFile(file, "rwd");
          raf.seek(startIndex);
          while ((len = is.read(buffer))!= -) {
            raf.write(buffer, , len);
            total += len;
            //每次讀取流里數(shù)據(jù)之后，把本次讀取的數(shù)據(jù)的長(zhǎng)度顯示至進(jìn)度條
            currentProgess += len;
            pb.setProgress(currentProgess);
            //發(fā)消息，讓主線程刷新文本進(jìn)度
            handler.sendEmptyMessage();
            //生成臨時(shí)文件保存下載進(jìn)度，用于斷點(diǎn)續(xù)傳，在所有線程現(xiàn)在完畢后刪除臨時(shí)文件
            RandomAccessFile progressRaf = new RandomAccessFile(progessFile, "rwd");
            progressRaf.write((total+"").getBytes());
            progressRaf.close();
          }
          raf.close();
          System.out.println("線程"+threadId+"下載完了");
          //當(dāng)所有線程都下在完了之后，刪除臨時(shí)進(jìn)度文件
          FinishedThread++;
          synchronized (Path) {
            if (FinishedThread==ThreadCount) {
              for (int i = ; i < ThreadCount; i++) {
                File f = new File(Environment.getExternalStorageDirectory(),i+".txt");
                f.delete();
              }
              FinishedThread=;
            }
          }
        }
      } catch (Exception e) {
        e.printStackTrace();
      }
    }
  }
}