Android的HTTP多线程下载示例代码

本示例介绍在Android平台下通过HTTP协议实现断点续传下载。

多线程断点需要的功能

1.多线程下载，

2.支持断点。

使用多线程的好处：使用多线程下载会提升文件下载的速度。

多线程下载文件的过程是： 

(1)首先获得下载文件的长度，然后设置本地文件的长度。

   HttpURLConnection.getContentLength();//获取下载文件的长度
  RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rwd");
    file.setLength(filesize);//设置本地文件的长度

(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。

如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如下图所示。

例如10M大小，使用3个线程来下载，

线程下载的数据长度   (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4M，第三个线程下载长度为2M

下载开始位置：线程id*每条线程下载的数据长度 = ?

下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

(3)使用Http的Range头字段指定每条线程从文件的什么位置开始下载，下载到什么位置为止，

如：指定从文件的2M位置开始下载，下载到位置(4M-1byte)为止

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

(4)保存文件，使用RandomAccessFile类指定每条线程从本地文件的什么位置开始写入数据。

RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");
threadfile.seek(2097152);//从文件的什么位置开始写入数据

MainActivity中代码:

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;
  
  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;
      }
    }
  };
  
  @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();
        }
      }
    });
  }
   
  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());//设置进度条的最大刻度为文件的长度
        try {
          loader.download(new DownloadProgressListener() {
            @Override
            public void onDownloadSize(int size) {//实时获知文件已经下载的数据长度
              Message msg = new Message();
              msg.what = 1;
              msg.getData().putInt("size", size);
              handler.sendMessage(msg);//发送消息
            }
          });
        } catch (Exception e) {
          handler.obtainMessage(-1).sendToTarget();
        }
      }
    }).start();
  }
} 

DBOpenHelper中代码： 

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);
  }
}

FileService中代码：

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);
  }
  
  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;
  }
  
  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();
  }
  
  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();
  }
  
  public void delete(String path){
    SQLiteDatabase db = openHelper.getWritableDatabase();
    db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});
    db.close();
  }
} 

DownloadProgressListener中代码：

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

FileDownloader中代码：

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;  
  
  private int downloadSize = 0;
  
  private int fileSize = 0;
  
  private DownloadThread[] threads;
  
  private File saveFile;
  
  private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
  
  private int block;
  
  private String downloadUrl;
  
  public int getThreadSize() {
    return threads.length;
  }
  
  public int getFileSize() {
    return fileSize;
  }
  
  protected synchronized void append(int size) {
    downloadSize += size;
  }
  
  protected synchronized void update(int threadId, int pos) {
    this.data.put(threadId, pos);
    this.fileService.update(this.downloadUrl, this.data);
  }
  
  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, *
  private String getFileName(HttpURLConnection conn) {
    String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);
    if(filename==null || "".equals(filename.trim())){//如果获取不到文件名称
      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";//默认取一个文件名
    }
    return filename;
  }
  
  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);//初始化每条线程已经下载的数据长度为0
        }
      }
      for (int i = 0; i < this.threads.length; i++) {//开启线程进行下载
        int downLength = this.data.get(i+1);
        if(downLength < this.block && this.downloadSize<this.fileSize){//判断线程是否已经完成下载,否则继续下载  
          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;//下载未完成
      while (notFinish) {// 循环判断所有线程是否完成下载
        Thread.sleep(900);
        notFinish = false;//假定全部线程下载完成
        for (int i = 0; i < this.threads.length; i++){
          if (this.threads[i] != null && !this.threads[i].isFinish()) {//如果发现线程未完成下载
            notFinish = true;//设置标志为下载没有完成
            if(this.threads[i].getDownLength() == -1){//如果下载失败,再重新下载
              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);//通知目前已经下载完成的数据长度
      }
      fileService.delete(this.downloadUrl);
    } catch (Exception e) {
      print(e.toString());
      throw new Exception("file download fail");
    }
    return this.downloadSize;
  }
  
  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;
  }
  
  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);
  }
} 

DownloadThread 中代码:

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;
  
  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){//未下载完成
      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, *
  public boolean isFinish() {
    return finish;
  }
  
  public long getDownLength() {
    return downLength;
  }
} 

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