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 getData(String path){
    SQLiteDatabase db = openHelper.getReadableDatabase();
    Cursor cursor = db.rawQuery("select threadid, downlength from filedownlog where downpath=?", new String[]{path});
    Map data = new HashMap();
    
    while(cursor.moveTonext()){
      data.put(cursor.getInt(0), cursor.getInt(1));
    }
    
    cursor.close();
    db.close();
    return data;
  }
  
  
  public void save(String path, Map map){//int threadid, int position
    SQLiteDatabase db = openHelper.getWritableDatabase();
    db.beginTransaction();
    
    try{
      for(Map.Entry 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 map){
    SQLiteDatabase db = openHelper.getWritableDatabase();
    db.beginTransaction();
    
    try{
      for(Map.Entry 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 data = new ConcurrentHashMap();
  
  
  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 getHttpResponseHeader(HttpURLConnection http) {
    Map header = new linkedHashMap();
    
    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 header = getHttpResponseHeader(http);
    
    for(Map.Entry 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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