Android入门：多线程断点下载详细介绍

本案例在于实现文件的多线程断点下载，即文件在下载一部分中断后，可继续接着已有进度下载，并通过进度条显示进度。也就是说在文件开始下载的同时，自动创建每个线程的下载进度的本地文件，下载中断后，重新进入应用点击下载，程序检查有没有本地文件的存在，若存在，获取本地文件中的下载进度，继续进行下载。当下载完成后，自动删除本地文件。

一、多线程断点下载介绍

所谓的多线程断点下载就是利用多线程下载，并且可被中断，如果突然没电了，重启手机后可以继续下载，而不需要重新下载；

利用的技术有：SQLite存储各个线程的下载量，HTTP请求获得下载数据；

二、辅助类介绍

为了完成多线程断点下载我们需要预先编写一些辅助类：

(1)DBOpenHelper

(2)FileService：
-Map<Integer,Integer> getData(String path); 根据URL获得各个线程的下载量
-save(String path, Map<Integer, Integer> map);存储URL对应的各个线程下载量，此函数为刚刚开始时调用
-update(String path, Map<Integer, Integer> map);更新数据库中URL对应的各个线程的下载量；
-delete(String path);删除URL对应的数据；

(3)FileDownloader:
-getFileSize()；获得下载文件的大小
-download(DownloadProgressListener listener);下载文件，并设置监听器

(4)DownloadThread:此类在FileDownloader的download中执行；

先将辅助类列出：
DBOpenHelper.Java

package 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 = "download.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.java

package service; 

import java.util.HashMap;
import java.util.Map; 

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
/**
 * 业务bean
 *
 */
public class FileService {
  private DBOpenHelper openHelper; 

  public FileService(Context context) {
    openHelper = new DBOpenHelper(context);
  }
  /**
   * 获取每条线程已经下载的文件长度
   * @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;
  }
  /**
   * 保存每条线程已经下载的文件长度
   * @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();
  }
  /**
   * 实时更新每条线程已经下载的文件长度
   * @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();
  }
  /**
   * 当文件下载完成后，删除对应的下载记录
   * @param path
   */
  public void delete(String path){
    SQLiteDatabase db = openHelper.getWritableDatabase();
    db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});
    db.close();
  } 

}

FileDownloader.java

package net.download; 

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 service.FileService;
import android.content.Context;
import android.util.Log;
/**
 * 文件下载器
 * FileDownloader loader = new FileDownloader(context, "http://browse.babasport.com/ejb3/ActivePort.exe",
        new File("D:\\androidsoft\\test"), 2);
    loader.getFileSize();//得到文件总大小
    try {
      loader.download(new DownloadProgressListener(){
        public void onDownloadSize(int size) {
          print("已经下载："+ size);
        }
      });
    } catch (Exception e) {
      e.printStackTrace();
    }
 */
public class FileDownloader {
  private static final String TAG = "FileDownloader";
  private Context context;
  private FileService fileService;
  /* 已下载文件长度 */
  private int downloadSize = 0;
  /* 原始文件长度 */
  private int fileSize = 0;
  /* 线程数 */
  private DownloadThread[] threads;
  /* 本地保存文件 */
  private File saveFile;
  /* 缓存各线程下载的长度*/
  private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
  /* 每条线程下载的长度 */
  private int block;
  /* 下载路径 */
  private String downloadUrl;
  /**
   * 获取线程数
   */
  public int getThreadSize() {
    return threads.length;
  }
  /**
   * 获取文件大小
   * @return
   */
  public int getFileSize() {
    return fileSize;
  }
  /**
   * 累计已下载大小
   * @param size
   */
  protected synchronized void append(int size) {
    downloadSize += size;
  }
  /**
   * 更新指定线程最后下载的位置
   * @param threadId 线程id
   * @param pos 最后下载的位置
   */
  protected synchronized void update(int threadId, int pos) {
    this.data.put(threadId, pos);
    this.fileService.update(this.downloadUrl, this.data);
  }
  /**
   * 构建文件下载器
   * @param downloadUrl 下载路径
   * @param fileSaveDir 文件保存目录
   * @param threadNum 下载线程数
   */
  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];
      //1.获得文件大小
      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();//根据响应获取文件大小
        if (this.fileSize <= 0) throw new RuntimeException("Unkown file size "); 

        String filename = getFileName(conn);//获取文件名称
        this.saveFile = new File(fileSaveDir, filename);//构建保存文件
        Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//获取下载记录 

        //2.如果以前已经下载过，则从数据库中导入记录，并继续下载 

        if(logdata.size()>0){//如果存在下载记录
          for(Map.Entry<Integer, Integer> entry : logdata.entrySet())
            data.put(entry.getKey(), entry.getValue());//把各条线程已经下载的数据长度放入data中
        }
        if(this.data.size()==this.threads.length){//下面计算所有线程已经下载的数据长度
          for (int i = 0; i < this.threads.length; i++) {
            this.downloadSize += this.data.get(i+1);
          }
          print("已经下载的长度"+ this.downloadSize);
        }
        //计算每条线程下载的数据长度
        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");
    }
  }
  /**
   * 获取文件名
   */
  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;
  } 

  /**
   * 开始下载文件
   * @param listener 监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null
   * @return 已下载文件大小
   * @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);
      //如果线程数与以前不一样，则重新开始下
      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;
  }
  /**
   * 获取Http响应头字段
   * @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头字段
   * @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);
  }
}

DownloadThread.java

package net.download; 

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;
  /* 下载开始位置 */
  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, */*");
        http.setRequestProperty("Accept-Language", "zh-CN");
        http.setRequestProperty("Referer", downUrl.toString());
        http.setRequestProperty("Charset", "UTF-8");
        int startPos = block * (threadId - 1) + downLength;//开始位置
        int endPos = block * threadId -1;//结束位置
        http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//设置获取实体数据的范围
        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);
  }
  /**
   * 下载是否完成
   * @return
   */
  public boolean isFinish() {
    return finish;
  }
  /**
   * 已经下载的内容大小
   * @return 如果返回值为-1,代表下载失败
   */
  public long getDownLength() {
    return downLength;
  }
}
DownloadProgressListener.java
package net.download; 

//下载监听器
public interface DownloadProgressListener {
  public void onDownloadSize(int size);
}

三、具体代码

效果如下：

实现代码：

package org.xiazdong.download; 

import java.io.File; 

import net.download.DownloadProgressListener;
import net.download.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.view.View.OnClickListener;
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 Button downloadButton;
  private EditText urlpathEditText;
  private TextView percentTextView;
  private ProgressBar progressBar;
  private Handler handler;
  //主线程
  private class UIHandler extends Handler{
    @Override
    public void handleMessage(Message msg) {
      int downloadsize = msg.getData().getInt("downloadsize");
      int percent = msg.getData().getInt("percent");
      progressBar.setProgress(downloadsize);
      percentTextView.setText(percent+"%");
    }
  }
  private OnClickListener listener = new OnClickListener() {
    DownloadThread thread;
    class DownloadThread extends Thread{
      private String url ;
      private File saveDir;
      private FileDownloader download;
      public DownloadThread(String url, File saveDir) {
        this.url = url;
        this.saveDir = saveDir;
      }
      //子线程
      @Override
      public void run() {
        download = new FileDownloader(MainActivity.this,url, saveDir, 3);
        progressBar.setMax(download.getFileSize()); //设置最大刻度
        try {
          download.download(downListener);
        } catch (Exception e) {
          e.printStackTrace();
        }
      }
    }
    //由子线程调用
    private DownloadProgressListener downListener = new DownloadProgressListener() {
      @Override
      public void onDownloadSize(int size) {
        //实时跟踪下载的情况
        int percent = (int)(((double)size)/progressBar.getMax()*100);
        Message msg = new Message();
        msg.what = 1;  //设置id
        System.out.println(percent+"%");
        System.out.println(size+"k");
        msg.getData().putInt("percent", percent);
        msg.getData().putInt("downloadsize",size);
        handler.sendMessage(msg); 

      }
    }; 

    @Override
    public void onClick(View v) {
      if(v==downloadButton){
        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
          String url = urlpathEditText.getText().toString();
          File saveDir = Environment.getExternalStorageDirectory();
          download(url,saveDir);
        }
        else{
          Toast.makeText(MainActivity.this, "SDCARD不存在", Toast.LENGTH_SHORT).show();
        }
      }
    } 

    private void download(String url, File saveDir) {
      thread = new DownloadThread(url,saveDir);
      thread.start(); 

    }
  };
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    downloadButton = (Button)findViewById(R.id.download);
    urlpathEditText = (EditText)findViewById(R.id.path);
    percentTextView = (TextView)findViewById(R.id.textView);
    progressBar = (ProgressBar)findViewById(R.id.progressBar);
    downloadButton.setOnClickListener(listener);
    handler = new UIHandler();
  }
}

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