public class Download {

  public static int threadCount = 5;  //线程开启的数量..
  public static void main(String[] args) {
    // TODO Auto-generated method stub

    String path = "http://192.168.199.172:8080/jdk.exe";
    try {
      URL url = new URL(path);
      HttpURLConnection conn = (HttpURLConnection) url.openConnection();
      conn.setRequestMethod("GET");
      conn.setConnectTimeout(5000);
      int status = conn.getResponseCode();
      
      if(status == 200){
        int length = conn.getContentLength();
      
        System.out.println(length);
        
        int blocksize = length/threadCount; //将文件长度进行平分..
        
        for(int threadID=1; threadID<=threadCount;threadID++){
          
          int startIndex = (threadID-1)*blocksize; //开始位置的求法..
          int endIndex = threadID*blocksize -1;   //结束位置的求法..
           
          /**
           * 如果一个文件的长度无法整除线程数..
           * 那么最后一个线程下载的结束位置需要设置文件末尾..
           * */
          if(threadID == threadCount){        
            endIndex = length;           
          }
          
          System.out.println("线程下载位置："+startIndex+"---"+endIndex);
        }
      }
      
      
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
  }
}

//下载线程的定义..  
public static class DownLoadThread implements Runnable{

    private int threadID;
    private int startIndex;
    private int endIndex;
    private String path;
    
    public DownLoadThread(int threadID,int startIndex,int endIndex,String path){
      
      this.threadID = threadID;
      this.startIndex = startIndex;
      this.endIndex = endIndex;
      this.path = path;
      
    }
    
    @Override
    public void run() {
      // TODO Auto-generated method stub
      
      try {
        
        //判断上一次是否下载完毕..如果没有下载完毕需要继续进行下载..这个文件记录了上一次的下载位置..
        File tempfile =new File(threadID+".txt");
        if(tempfile.exists() && tempfile.length()>0){
          
          FileInputStream fis = new FileInputStream(tempfile);
          byte buffer[] = new byte[1024];
          int leng = fis.read(buffer);
          int downlength = Integer.parseInt(new String(buffer,0,leng));//从上次下载后的位置开始下载..重新拟定开始下载的位置..
          startIndex = downlength;
          fis.close();
        }
        
        URL url = new URL(path);
        HttpURLConnection conn =(HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(5000);
        conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex);
        
        int status = conn.getResponseCode();
        //206也表示服务器响应成功..
        if(status == 206){
          
          //获取服务器返回的I/O流..然后将数据写入文件当中..
          InputStream in = conn.getInputStream();
          
          //文件写入开始..用来保存当前需要下载的文件..
          RandomAccessFile raf = new RandomAccessFile("jdk.exe", "rwd");
          raf.seek(startIndex);
          
          
          int len = 0;
          byte buf[] =new byte[1024];
          
          //记录已经下载的长度..
          int total = 0;
          
          while((len = in.read(buf))!=-1){
            
            //用于记录当前下载的信息..
            RandomAccessFile file =new RandomAccessFile(threadID+".txt", "rwd");
            total += len;
            file.write((total+startIndex+"").getBytes());
            file.close();
            //将数据写入文件当中..
            raf.write(buf, 0, len);
            
          }
          in.close();
          raf.close();
          
          
        }  
        
      } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      }finally{
        //如果所有的线程全部下载完毕后..也就是任务完成..清除掉所有原来的记录文件..
        runningThread -- ;
        if(runningThread==0){
          for(int i=1;i<threadCount;i++){
            File file = new File(i+".txt");
            file.delete();
          }
        }
      }
    }
  }

package com.example.mutithread;

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.text.TextUtils;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {

  private EditText et;
  private ProgressBar pb;
  public static int threadCount = 5;
  public static int runningThread=5;
  public int currentProgress=0; //当前进度值..
  private TextView tv;
  
  
  private Handler handler = new Handler(){
    
    @Override
    public void handleMessage(Message msg){
      switch (msg.what) {
      case 1:
        Toast.makeText(getApplicationContext(), msg.obj.toString(), 0).show();
        break;
      case 2:
        break;
      case 3:
        tv.setText("当前进度："+(pb.getProgress()*100)/pb.getMax());
      default:
        break;
      }
    }
  };
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    et = (EditText) findViewById(R.id.et);
    pb =(ProgressBar) findViewById(R.id.pg);
    tv= (TextView) findViewById(R.id.tv);
  }

  public void downLoad(View v){
    final String path = et.getText().toString().trim();
    if(TextUtils.isEmpty(path)){
      Toast.makeText(this, "下载路径错误", Toast.LENGTH_LONG).show();
      return ;
    }
    
    new Thread(){
//      String path = "http://192.168.199.172:8080/jdk.exe";
      public void run(){
        try {
          URL url = new URL(path);
          HttpURLConnection conn = (HttpURLConnection) url.openConnection();
          conn.setRequestMethod("GET");
          conn.setConnectTimeout(5000);
          int status = conn.getResponseCode();
          
          if(status == 200){
            int length = conn.getContentLength();
            System.out.println("文件总长度"+length);
            pb.setMax(length);
            
            
            RandomAccessFile raf = new RandomAccessFile("/sdcard/setup.exe","rwd");
            raf.setLength(length);
            raf.close();
            
            
            //开启5个线程来下载当前资源..
            int blockSize = length/threadCount ;
            
            for(int threadID=1;threadID<=threadCount;threadID++){
              
              int startIndex = (threadID-1)*blockSize;
              int endIndex = threadID*blockSize -1;
              
              if(threadID == threadCount){
                endIndex = length; 
              }
              System.out.println("线程"+threadID+"下载:---"+startIndex+"--->"+endIndex);
              new Thread(new DownLoadThread(threadID, startIndex, endIndex, path)).start() ;
            }
          }
          
          
        } catch (Exception e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
        }
      };
      
    }.start();
  }
  /** 
   * 下载线程..
   * */
  public class DownLoadThread implements Runnable{

    private int ThreadID;
    private int startIndex;
    private int endIndex;
    private String path;
    
    public DownLoadThread(int ThreadID,int startIndex,int endIndex,String path){
      this.ThreadID = ThreadID;
      this.startIndex = startIndex;
      this.endIndex = endIndex;
      this.path = path;
    }
    @Override
    public void run() {
      // TODO Auto-generated method stub
      URL url;
      try {    
        //检查是否存在还未下载完成的文件...
        File tempfile = new File("/sdcard/"+ThreadID+".txt");
        if(tempfile.exists() && tempfile.length()>0){
          FileInputStream fis = new FileInputStream(tempfile);
          byte temp[] =new byte[1024];
          int leng = fis.read(temp);
          int downlength = Integer.parseInt(new String(temp,0,leng));
          
          int alreadydown = downlength -startIndex;
          
          currentProgress += alreadydown;//发生断点之后记录下载的文件长度..
          
          startIndex = downlength;
          fis.close();
        }
        
        
        url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setRequestProperty("Range", "bytes="+startIndex+"-"+endIndex);
        conn.setConnectTimeout(5000);
        
        //获取响应码..
        int status =conn.getResponseCode();
        
        if(status == 206){
          InputStream in = conn.getInputStream();
          RandomAccessFile raf =new RandomAccessFile("/sdcard/jdk.exe", "rwd");
          
          //文件开始写入..
          raf.seek(startIndex);
          
          int len =0;
          byte[] buffer =new byte[1024];
          
          //已经下载的数据长度..
          int total = 0;
          
          
          while((len = in.read(buffer))!=-1){
            //记录当前数据下载的长度...
            RandomAccessFile file = new RandomAccessFile("/sdcard/"+ThreadID+".txt", "rwd");
            
            raf.write(buffer, 0, len);
            total += len;
            System.out.println("线程"+ThreadID+"total:"+total);
            file.write((total+startIndex+"").getBytes());
            file.close();
            
            synchronized (MainActivity.this) {
              currentProgress += len; //获取当前总进度...
               //progressBar progressDialog可以直接在子线程内部更新UI..由于源码内部进行了特殊的处理..
               pb.setProgress(currentProgress); //更改界面上的进度条进度..
               Message msg =Message.obtain(); //复用以前的消息..避免多次new...
               msg.what = 3;
               handler.sendMessage(msg);
               
            }
          }
          raf.close();
          in.close();
          System.out.println("线程："+ThreadID+"下载完毕");
        }else{
          System.out.println("线程："+ThreadID+"下载失败");
        }
        
      } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        Message msg = new Message();
        msg.what = 1;
        msg.obj = e;
        handler.sendMessage(msg);
      }finally{
        synchronized (MainActivity.this) {
          runningThread--;
          
          if(runningThread == 0){
            for(int i=1;i<=threadCount;i++){
              File file = new File("/sdcard/"+i+".txt");
              file.delete();
            }
            Message msg =new Message();
            msg.what = 2;
            msg.obj ="下载完毕";
            handler.sendMessage(msg);
          }
        }  
        
      }
  
    }
    
  }
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
  }

}

 private synchronized void refreshProgress(int id, int progress, boolean fromUser) {
    if (mUiThreadId == Thread.currentThread().getId()) { //如果当前运行的线程和主线程相同..那么更新进度条..
      doRefreshProgress(id, progress, fromUser, true);
    } else { //如果不满足上面说的情况..
      if (mRefreshProgressRunnable == null) {
        mRefreshProgressRunnable = new RefreshProgressRunnable();//那么新建立一个线程..然后执行下面的过程..
      }

      final RefreshData rd = RefreshData.obtain(id, progress, fromUser); //获取消息队列中的消息..
      mRefreshData.add(rd);
      if (mAttached && !mRefreshIsPosted) {
        post(mRefreshProgressRunnable); //主要是这个地方..调用了post方法..将当前运行的线程发送到消息队列当中..那么这个线程就可以在UI中运行了..因此这一步是决定因素..
        mRefreshIsPosted = true;
      }
    }
  }