HttpURLConnection.getContentLength();//獲取下載文件的長度
  RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rwd");
    file.setLength(filesize);//設(shè)置本地文件的長度

HttpURLConnection.setRequestProperty("Range", "bytes=2097152-4194303");

RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");
threadfile.seek(2097152);//從文件的什么位置開始寫入數(shù)據(jù)

package com.android.downloader;
import java.io.File;

import com.android.network.DownloadProgressListener;
import com.android.network.FileDownloader;

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
  private EditText downloadpathText;
  private TextView resultView;
  private ProgressBar progressBar;
  
  /**
   * 當(dāng)Handler被創(chuàng)建會(huì)關(guān)聯(lián)到創(chuàng)建它的當(dāng)前線程的消息隊(duì)列，該類用于往消息隊(duì)列發(fā)送消息
   * 消息隊(duì)列中的消息由當(dāng)前線程內(nèi)部進(jìn)行處理
   */
  private Handler handler = new Handler(){

    @Override
    public void handleMessage(Message msg) {      
      switch (msg.what) {
      case 1:        
        progressBar.setProgress(msg.getData().getInt("size"));
        float num = (float)progressBar.getProgress()/(float)progressBar.getMax();
        int result = (int)(num*100);
        resultView.setText(result+ "%");
        
        if(progressBar.getProgress()==progressBar.getMax()){
          Toast.makeText(MainActivity.this, R.string.success, 1).show();
        }
        break;
      case -1:
        Toast.makeText(MainActivity.this, R.string.error, 1).show();
        break;
      }
    }
  };
  
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    
    downloadpathText = (EditText) this.findViewById(R.id.path);
    progressBar = (ProgressBar) this.findViewById(R.id.downloadbar);
    resultView = (TextView) this.findViewById(R.id.resultView);
    Button button = (Button) this.findViewById(R.id.button);
    
    button.setOnClickListener(new View.OnClickListener() {
      
      @Override
      public void onClick(View v) {
        // TODO Auto-generated method stub
        String path = downloadpathText.getText().toString();
        System.out.println(Environment.getExternalStorageState()+"------"+Environment.MEDIA_MOUNTED);
        
        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
          download(path, Environment.getExternalStorageDirectory());
        }else{
          Toast.makeText(MainActivity.this, R.string.sdcarderror, 1).show();
        }
      }
    });
  }
  
   /**
    * 主線程(UI線程)
    * 對(duì)于顯示控件的界面更新只是由UI線程負(fù)責(zé)，如果是在非UI線程更新控件的屬性值，更新后的顯示界面不會(huì)反映到屏幕上
    * @param path
    * @param savedir
    */
  private void download(final String path, final File savedir) {
    new Thread(new Runnable() {      
      @Override
      public void run() {
        FileDownloader loader = new FileDownloader(MainActivity.this, path, savedir, 3);
        progressBar.setMax(loader.getFileSize());//設(shè)置進(jìn)度條的最大刻度為文件的長度
        
        try {
          loader.download(new DownloadProgressListener() {
            @Override
            public void onDownloadSize(int size) {//實(shí)時(shí)獲知文件已經(jīng)下載的數(shù)據(jù)長度
              Message msg = new Message();
              msg.what = 1;
              msg.getData().putInt("size", size);
              handler.sendMessage(msg);//發(fā)送消息
            }
          });
        } catch (Exception e) {
          handler.obtainMessage(-1).sendToTarget();
        }
      }
    }).start();
  }
} 

package com.android.service;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBOpenHelper extends SQLiteOpenHelper {
  private static final String DBNAME = "down.db";
  private static final int VERSION = 1;
  
  public DBOpenHelper(Context context) {
    super(context, DBNAME, null, VERSION);
  }
  
  @Override
  public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE IF NOT EXISTS filedownlog (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER, downlength INTEGER)");
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS filedownlog");
    onCreate(db);
  }
}

package com.android.service;
import java.util.HashMap;
import java.util.Map;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class FileService {
  private DBOpenHelper openHelper;

  public FileService(Context context) {
    openHelper = new DBOpenHelper(context);
  }
  
  /**
   * 獲取每條線程已經(jīng)下載的文件長度
   * @param path
   * @return
   */
  public Map<Integer, Integer> getData(String path){
    SQLiteDatabase db = openHelper.getReadableDatabase();
    Cursor cursor = db.rawQuery("select threadid, downlength from filedownlog where downpath=?", new String[]{path});
    Map<Integer, Integer> data = new HashMap<Integer, Integer>();
    
    while(cursor.moveToNext()){
      data.put(cursor.getInt(0), cursor.getInt(1));
    }
    
    cursor.close();
    db.close();
    return data;
  }
  
  /**
   * 保存每條線程已經(jīng)下載的文件長度
   * @param path
   * @param map
   */
  public void save(String path, Map<Integer, Integer> map){//int threadid, int position
    SQLiteDatabase db = openHelper.getWritableDatabase();
    db.beginTransaction();
    
    try{
      for(Map.Entry<Integer, Integer> entry : map.entrySet()){
        db.execSQL("insert into filedownlog(downpath, threadid, downlength) values(?,?,?)",
            new Object[]{path, entry.getKey(), entry.getValue()});
      }
      db.setTransactionSuccessful();
    }finally{
      db.endTransaction();
    }
    
    db.close();
  }
  
  /**
   * 實(shí)時(shí)更新每條線程已經(jīng)下載的文件長度
   * @param path
   * @param map
   */
  public void update(String path, Map<Integer, Integer> map){
    SQLiteDatabase db = openHelper.getWritableDatabase();
    db.beginTransaction();
    
    try{
      for(Map.Entry<Integer, Integer> entry : map.entrySet()){
        db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?",
            new Object[]{entry.getValue(), path, entry.getKey()});
      }
      
      db.setTransactionSuccessful();
    }finally{
      db.endTransaction();
    }
    
    db.close();
  }
  
  /**
   * 當(dāng)文件下載完成后，刪除對(duì)應(yīng)的下載記錄
   * @param path
   */
  public void delete(String path){
    SQLiteDatabase db = openHelper.getWritableDatabase();
    db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});
    db.close();
  }
} 

package com.android.network;
public interface DownloadProgressListener {
  public void onDownloadSize(int size);
} 

package com.android.network;
import java.io.File;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import com.android.service.FileService;

import android.content.Context;
import android.util.Log;

public class FileDownloader {
  private static final String TAG = "FileDownloader";
  private Context context;
  private FileService fileService;  
  
  /* 已下載文件長度 */
  private int downloadSize = 0;
  
  /* 原始文件長度 */
  private int fileSize = 0;
  
  /* 線程數(shù) */
  private DownloadThread[] threads;
  
  /* 本地保存文件 */
  private File saveFile;
  
  /* 緩存各線程下載的長度*/
  private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
  
  /* 每條線程下載的長度 */
  private int block;
  
  /* 下載路徑 */
  private String downloadUrl;
  
  /**
   * 獲取線程數(shù)
   */
  public int getThreadSize() {
    return threads.length;
  }
  
  /**
   * 獲取文件大小
   * @return
   */
  public int getFileSize() {
    return fileSize;
  }
  
  /**
   * 累計(jì)已下載大小
   * @param size
   */
  protected synchronized void append(int size) {
    downloadSize += size;
  }
  
  /**
   * 更新指定線程最后下載的位置
   * @param threadId 線程id
   * @param pos 最后下載的位置
   */
  protected synchronized void update(int threadId, int pos) {
    this.data.put(threadId, pos);
    this.fileService.update(this.downloadUrl, this.data);
  }
  
  /**
   * 構(gòu)建文件下載器
   * @param downloadUrl 下載路徑
   * @param fileSaveDir 文件保存目錄
   * @param threadNum 下載線程數(shù)
   */
  public FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) {
    try {
      this.context = context;
      this.downloadUrl = downloadUrl;
      fileService = new FileService(this.context);
      URL url = new URL(this.downloadUrl);
      if(!fileSaveDir.exists()) fileSaveDir.mkdirs();
      this.threads = new DownloadThread[threadNum];          
      
      HttpURLConnection conn = (HttpURLConnection) url.openConnection();
      conn.setConnectTimeout(5*1000);
      conn.setRequestMethod("GET");
      conn.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
      conn.setRequestProperty("Accept-Language", "zh-CN");
      conn.setRequestProperty("Referer", downloadUrl); 
      conn.setRequestProperty("Charset", "UTF-8");
      conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
      conn.setRequestProperty("Connection", "Keep-Alive");
      conn.connect();
      printResponseHeader(conn);
      
      if (conn.getResponseCode()==200) {
        this.fileSize = conn.getContentLength();//根據(jù)響應(yīng)獲取文件大小
        if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");
            
        String filename = getFileName(conn);//獲取文件名稱
        this.saveFile = new File(fileSaveDir, filename);//構(gòu)建保存文件
        Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//獲取下載記錄
        
        if(logdata.size()>0){//如果存在下載記錄
          for(Map.Entry<Integer, Integer> entry : logdata.entrySet())
            data.put(entry.getKey(), entry.getValue());//把各條線程已經(jīng)下載的數(shù)據(jù)長度放入data中
        }
        
        if(this.data.size()==this.threads.length){//下面計(jì)算所有線程已經(jīng)下載的數(shù)據(jù)長度
          for (int i = 0; i < this.threads.length; i++) {
            this.downloadSize += this.data.get(i+1);
          }
          
          print("已經(jīng)下載的長度"+ this.downloadSize);
        }
        
        //計(jì)算每條線程下載的數(shù)據(jù)長度
        this.block = (this.fileSize % this.threads.length)==0? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1;
      }else{
        throw new RuntimeException("server no response ");
      }
    } catch (Exception e) {
      print(e.toString());
      throw new RuntimeException("don't connection this url");
    }
  }
  
  /**
   * 獲取文件名
   * @param conn
   * @return
   */
  private String getFileName(HttpURLConnection conn) {
    String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);
    
    if(filename==null || "".equals(filename.trim())){//如果獲取不到文件名稱
      for (int i = 0;; i++) {
        String mine = conn.getHeaderField(i);
        
        if (mine == null) break;
        
        if("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())){
          Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase());
          if(m.find()) return m.group(1);
        }
      }
      
      filename = UUID.randomUUID()+ ".tmp";//默認(rèn)取一個(gè)文件名
    }
    
    return filename;
  }
  
  /**
   * 開始下載文件
   * @param listener 監(jiān)聽下載數(shù)量的變化,如果不需要了解實(shí)時(shí)下載的數(shù)量,可以設(shè)置為null
   * @return 已下載文件大小
   * @throws Exception
   */
  public int download(DownloadProgressListener listener) throws Exception{
    try {
      RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");
      if(this.fileSize>0) randOut.setLength(this.fileSize);
      randOut.close();
      URL url = new URL(this.downloadUrl);
      
      if(this.data.size() != this.threads.length){
        this.data.clear();
        
        for (int i = 0; i < this.threads.length; i++) {
          this.data.put(i+1, 0);//初始化每條線程已經(jīng)下載的數(shù)據(jù)長度為0
        }
      }
      
      for (int i = 0; i < this.threads.length; i++) {//開啟線程進(jìn)行下載
        int downLength = this.data.get(i+1);
        
        if(downLength < this.block && this.downloadSize<this.fileSize){//判斷線程是否已經(jīng)完成下載,否則繼續(xù)下載  
          this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
          this.threads[i].setPriority(7);
          this.threads[i].start();
        }else{
          this.threads[i] = null;
        }
      }
      
      this.fileService.save(this.downloadUrl, this.data);
      boolean notFinish = true;//下載未完成
      
      while (notFinish) {// 循環(huán)判斷所有線程是否完成下載
        Thread.sleep(900);
        notFinish = false;//假定全部線程下載完成
        
        for (int i = 0; i < this.threads.length; i++){
          if (this.threads[i] != null && !this.threads[i].isFinish()) {//如果發(fā)現(xiàn)線程未完成下載
            notFinish = true;//設(shè)置標(biāo)志為下載沒有完成
            
            if(this.threads[i].getDownLength() == -1){//如果下載失敗,再重新下載
              this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
              this.threads[i].setPriority(7);
              this.threads[i].start();
            }
          }
        }  
        
        if(listener!=null) listener.onDownloadSize(this.downloadSize);//通知目前已經(jīng)下載完成的數(shù)據(jù)長度
      }
      
      fileService.delete(this.downloadUrl);
    } catch (Exception e) {
      print(e.toString());
      throw new Exception("file download fail");
    }
    return this.downloadSize;
  }
  
  /**
   * 獲取Http響應(yīng)頭字段
   * @param http
   * @return
   */
  public static Map<String, String> getHttpResponseHeader(HttpURLConnection http) {
    Map<String, String> header = new LinkedHashMap<String, String>();
    
    for (int i = 0;; i++) {
      String mine = http.getHeaderField(i);
      if (mine == null) break;
      header.put(http.getHeaderFieldKey(i), mine);
    }
    
    return header;
  }
  
  /**
   * 打印Http頭字段
   * @param http
   */
  public static void printResponseHeader(HttpURLConnection http){
    Map<String, String> header = getHttpResponseHeader(http);
    
    for(Map.Entry<String, String> entry : header.entrySet()){
      String key = entry.getKey()!=null ? entry.getKey()+ ":" : "";
      print(key+ entry.getValue());
    }
  }

  private static void print(String msg){
    Log.i(TAG, msg);
  }
} 

package com.android.network;
import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

import android.util.Log;

public class DownloadThread extends Thread {
  private static final String TAG = "DownloadThread";
  private File saveFile;
  private URL downUrl;
  private int block;
  
  /* 下載開始位置 */
  private int threadId = -1;  
  private int downLength;
  private boolean finish = false;
  private FileDownloader downloader;
  
  public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downLength, int threadId) {
    this.downUrl = downUrl;
    this.saveFile = saveFile;
    this.block = block;
    this.downloader = downloader;
    this.threadId = threadId;
    this.downLength = downLength;
  }
  
  @Override
  public void run() {
    if(downLength < block){//未下載完成
      try {
        HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();
        http.setConnectTimeout(5 * 1000);
        http.setRequestMethod("GET");
        http.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
        http.setRequestProperty("Accept-Language", "zh-CN");
        http.setRequestProperty("Referer", downUrl.toString()); 
        http.setRequestProperty("Charset", "UTF-8");
        int startPos = block * (threadId - 1) + downLength;//開始位置
        int endPos = block * threadId -1;//結(jié)束位置
        http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//設(shè)置獲取實(shí)體數(shù)據(jù)的范圍
        http.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
        http.setRequestProperty("Connection", "Keep-Alive");
        
        InputStream inStream = http.getInputStream();
        byte[] buffer = new byte[1024];
        int offset = 0;
        print("Thread " + this.threadId + " start download from position "+ startPos);
        RandomAccessFile threadfile = new RandomAccessFile(this.saveFile, "rwd");
        threadfile.seek(startPos);
        
        while ((offset = inStream.read(buffer, 0, 1024)) != -1) {
          threadfile.write(buffer, 0, offset);
          downLength += offset;
          downloader.update(this.threadId, downLength);
          downloader.append(offset);
        }
        
        threadfile.close();
        inStream.close();
        print("Thread " + this.threadId + " download finish");
        this.finish = true;
      } catch (Exception e) {
        this.downLength = -1;
        print("Thread "+ this.threadId+ ":"+ e);
      }
    }
  }
  
  private static void print(String msg){
    Log.i(TAG, msg);
  }
  
  /**
   * 下載是否完成
   * @return
   */
  public boolean isFinish() {
    return finish;
  }
  
  /**
   * 已經(jīng)下載的內(nèi)容大小
   * @return 如果返回值為-1,代表下載失敗
   */
  public long getDownLength() {
    return downLength;
  }
}