android 多线程下载

我们编写的是Andorid的HTTP多线程断点下载应用程序。因为之间我们学习的学习积累，直接使用单线程下载HTTP文件对我们来说是一件非常简单的事。那么，多线程断点下载的难点在哪里？1.多线程下载，2.支持断点。

多线程下载：

如何才能从文件的指定位置处开始下载文件？（比如从50MB开始）这一点我们可以通过HTTP请求信息头来设置，还记得HTTP请求信息头的“Range”属性吗？

断点：

首要问题（多线程下载）已经被我们解决了，支持断点下载想必大家也已经想到了。就是将下载的进度保存到文件中，但在Android中却不能这么做。通过老黎的试验，在Android平台中，我们需要向文件中写出下载的文件数据，还需要向另一个文件中写出下载进度，这样会出错。这样会导致有一个文件的内容没有被写出。所以我们就不能以文件的方式来保存下载进度，但可以通过数据库的方式保存下载进度。

这两大问题我们已经有了解决思路，那么就开始动手编写吧！

1.创建Android工程

Project name:MulThreadDownloader

BuildTarget:Android2.1

Application name：多线程断点下载

Package name:com.changcheng.download

Create Activity:MulThreadDownloader

Min SDK Version:7

2.AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

      package="com.changcheng.download"

      android:versionCode="1"

      android:versionName="1.0">

    <application android:icon="@drawable/icon" android:label="@string/app_name">

        <activity android:name=".MulThreadDownloader"

                  android:label="@string/app_name">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

    </application>

    <uses-sdk android:minSdkVersion="7" />

         <!-- 在SDCard中创建与删除文件权限 -->

         <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>

         <!-- 往SDCard写入数据权限 -->

         <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

         <!-- 访问internet权限 -->

         <uses-permission android:name="android.permission.INTERNET"/>       

</manifest>

3.strings.xml

<?xml version="1.0" encoding="utf-8"?>

<resources>

    <string name="hello">Hello World, DownloadActivity!</string>

    <string name="app_name">多线程断点下载</string>

    <string name="path">下载路径</string>

    <string name="downloadbutton">下载</string>

    <string name="sdcarderror">SDCard不存在或者写保护</string>

</resources>

4.main.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    >

    <!-- 下载路径 -->

         <TextView 

             android:layout_width="fill_parent"

             android:layout_height="wrap_content"

             android:text="@string/path"

             />

    <EditText

             android:layout_width="fill_parent"

             android:layout_height="wrap_content"

             android:text="http://www.winrar.com.cn/download/wrar380sc.exe"

             android:id="@+id/path"

             />

         <!-- 下载按钮 -->

         <Button

                   android:layout_width="wrap_content"

             android:layout_height="wrap_content"

             android:text="@string/downloadbutton"

             android:id="@+id/button"

             />

          <!-- 进度条 -->

          <ProgressBar

                   android:layout_width="fill_parent"

             android:layout_height="20dip"

             style="?android:attr/progressBarStyleHorizontal"

                 android:id="@+id/downloadbar"/>

       <!-- 进度% -->    

       <TextView 

             android:layout_width="fill_parent"

             android:layout_height="wrap_content"

             android:gravity="center"

             android:id="@+id/resultView"

             />

</LinearLayout>

5.MulThreadDownloader

package com.changcheng.download;

 

import java.io.File;

import com.changcheng.net.download.DownloadProgressListener;

import com.changcheng.net.download.FileDownloader;

import com.changcheng.download.R;

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 MulThreadDownloader extends Activity {

         private EditText pathText;

         private ProgressBar progressBar;

         private TextView resultView;

         private Handler handler = new Handler(){

                   @Override

                   public void handleMessage(Message msg) {

                            if(!Thread.currentThread().isInterrupted()){

                                     switch (msg.what) {

                                     case 1:

                                               // 获取当前文件下载的进度

                                               int size = msg.getData().getInt("size");

                                               progressBar.setProgress(size);

                                               int result = (int)(((float)size/(float)progressBar.getMax()) * 100);

                                               resultView.setText(result+ "%");

                                               if(progressBar.getMax() == size){

                                                        Toast.makeText(MulThreadDownloader.this, "文件下载完成", 1).show();

                                               }

                                               break;

        

                                     case -1:

                                               String error = msg.getData().getString("error");

                                               Toast.makeText(MulThreadDownloader.this, error, 1).show();

                                               break;

                                     }                          

                            }

                            super.handleMessage(msg);

                   }                 

         };

        

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        pathText = (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) {

                                     String path = pathText.getText().toString();

                                     if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){

                                               //下载文件需要很长的时间，主线程是不能够长时间被阻塞，如果主线程被长时间阻塞， 那么Android被回收应用

                                               download(path, Environment.getExternalStorageDirectory());

                                     }else{

                                               Toast.makeText(MulThreadDownloader.this, R.string.sdcarderror, 1).show();

                                     }

                            }

                   });

    }

    /**

     * 下载文件

     * @param path 下载路径

     * @param saveDir 文件保存目录

     */

  //对于Android的UI控件，只能由主线程负责显示界面的更新，其他线程不能直接更新UI控件的显示

    public void download(final String path, final File saveDir){

       new Thread(new Runnable() {                         

                            @Override

                            public void run() {

                                     FileDownloader downer = new FileDownloader(MulThreadDownloader.this, path, saveDir, 3);

                                     progressBar.setMax(downer.getFileSize());//设置进度条的最大刻度

                                     try {

                                               downer.download(new DownloadProgressListener(){

                                                        @Override

                                                        public void onDownloadSize(int size) {

                                                                 Message msg = new Message();

                                                                 msg.what = 1;

                                                                 msg.getData().putInt("size", size);

                                                                 handler.sendMessage(msg);//发送消息

                                                        }});

                                     } catch (Exception e) {

                                               Message msg = new Message();

                                               msg.what = -1;

                                               msg.getData().putString("error", "下载失败");

                                               handler.sendMessage(msg);

                                     }

                            }

                   }).start();

    }

}

6.FileDownload

package com.changcheng.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 com.changcheng.download.service.FileService;

import android.content.Context;

import android.util.Log;

 

/**

 * 文件下载器

 * @author [e-mail]

 *

 */

public class FileDownloader {

         private Context context;

         private FileService fileService;

        

         private static final String TAG = "FileDownloader";

         /* 已下载文件大小 */

         private int downloadSize = 0;

         /* 原始文件大小 */

         private int fileSize = 0;

         /* 线程数 */

         private DownloadThread[] threads;

         /* 下载路径  */

         private URL url;

         /* 本地保存文件 */

         private File saveFile;

         /* 下载记录文件 */

         private File logFile;

         /* 缓存各线程最后下载的位置*/

         private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();

         /* 每条线程下载的大小 */

         private int block;

         private String downloadUrl;//下载路径

         /**

          * 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 void update(int threadId, int pos) {

                   this.data.put(threadId, pos);

         }

         /**

          * 保存记录文件

          */

         protected synchronized void saveLogFile() {

                   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(context);

                            this.url = new URL(downloadUrl);

                            if(!fileSaveDir.exists()) fileSaveDir.mkdirs();

                            this.threads = new DownloadThread[threadNum];                                        

                            HttpURLConnection conn = (HttpURLConnection) url.openConnection();

                            conn.setConnectTimeout(6*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("无法获知文件大小 ");

                                                       

                                     String filename = getFileName(conn);

                                     this.saveFile = new File(fileSaveDir, filename);/* 保存文件 */

                                     Map<Integer, Integer> logdata = fileService.getData(downloadUrl);

                                     if(logdata.size()>0){

                                               data.putAll(logdata);

                                     }

                                     this.block = this.fileSize / this.threads.length + 1;

                                     if(this.data.size()==this.threads.length){

                                               for (int i = 0; i < this.threads.length; i++) {

                                                        this.downloadSize += this.data.get(i+1)-(this.block * i);

                                               }

                                               print("已经下载的长度"+ this.downloadSize);

                                     }                                   

                            }else{

                                     throw new RuntimeException("服务器响应错误 ");

                            }

                   } catch (Exception e) {

                            print(e.toString());

                            throw new RuntimeException("连接不到下载路径 ");

                   }

         }

         /**

          * 获取文件名

          */

         private String getFileName(HttpURLConnection conn) {

                   String filename = this.url.toString().substring(this.url.toString().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 {                    

                            if(this.data.size() != this.threads.length){

                                     this.data.clear();

                                     for (int i = 0; i < this.threads.length; i++) {

                                               this.data.put(i+1, this.block * i);

                                     }

                            }

                            for (int i = 0; i < this.threads.length; i++) {

                                     int downLength = this.data.get(i+1) - (this.block * i);

                                     if(downLength < this.block && this.data.get(i+1)<this.fileSize){ //该线程未完成下载时,继续下载

                                               RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");

                                               if(this.fileSize>0) randOut.setLength(this.fileSize);                               

                                               randOut.seek(this.data.get(i+1));

                                               this.threads[i] = new DownloadThread(this, this.url, randOut, 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) {// 循环判断是否下载完毕

                                     Thread.sleep(900);

                                     notFinish = false;//假定下载完成

                                     for (int i = 0; i < this.threads.length; i++){

                                               if (this.threads[i] != null && !this.threads[i].isFinish()) {

                                                        notFinish = true;//下载没有完成

                                                        if(this.threads[i].getDownLength() == -1){//如果下载失败,再重新下载

                                                                 RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");

                                                                 randOut.seek(this.data.get(i+1));

                                                                 this.threads[i] = new DownloadThread(this, this.url, randOut, 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);

                            }

                            fileService.delete(this.downloadUrl);

                   } catch (Exception e) {

                            print(e.toString());

                            throw new Exception("下载失败");

                   }

                   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);

         }

}

7.DownloadProgressListener

package com.changcheng.net.download;

 

public interface DownloadProgressListener {

         public void onDownloadSize(int size);

}

8.FileService

package com.changcheng.download.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);

         }

         /**

          * 获取线程最后下载位置

          * @param path

          * @return

          */

         public Map<Integer, Integer> getData(String path){

                   SQLiteDatabase db = openHelper.getReadableDatabase();

                   Cursor cursor = db.rawQuery("select threadid, position from filedown 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;

         }

         /**

          * 保存下载线程初始位置

          * @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 filedown(downpath, threadid, position) values(?,?,?)",

                                                        new Object[]{path, entry.getKey(), entry.getValue()});

                            }

                            db.setTransactionSuccessful();

                   }finally{

                            db.endTransaction();

                   }

                   db.close();

         }

         /**

          * 实时更新线程的最后下载位置

          * @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 filedown set position=? 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，清掉该文件对应的下载记录

          * @param path

          */

         public void delete(String path){

                   SQLiteDatabase db = openHelper.getWritableDatabase();

                   db.execSQL("delete from filedown where downpath=?", new Object[]{path});

                   db.close();

         }

        

}
 

9.DownloadThread

package com.changcheng.net.download;

 

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 RandomAccessFile saveFile;

         private URL downUrl;

         private int block;

         /* 下载开始位置  */

         private int threadId = -1;

         private int startPos;

         private int downLength;

         private boolean finish = false;

         private FileDownloader downloader;

 

         public DownloadThread(FileDownloader downloader, URL downUrl, RandomAccessFile saveFile, int block, int startPos, int threadId) {

                   this.downUrl = downUrl;

                   this.saveFile = saveFile;

                   this.block = block;

                   this.startPos = startPos;

                   this.downloader = downloader;

                   this.threadId = threadId;

                   this.downLength = startPos - (block * (threadId - 1));

         }

        

         @Override

         public void run() {

                   if(downLength < block){//未下载完成

                            try {

                                      HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();

                                     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");

                                     http.setRequestProperty("Range", "bytes=" + this.startPos + "-");

                                     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();

                                     int max = block>1024 ? 1024 : (block>10 ? 10 : 1);

                                     byte[] buffer = new byte[max];

                                     int offset = 0;

                                     print("线程 " + this.threadId + "从位置"+ this.startPos+ "开始下载 ");

                                     while (downLength < block && (offset = inStream.read(buffer, 0, max)) != -1) {

                                               saveFile.write(buffer, 0, offset);

                                               downLength += offset;

                                               downloader.update(this.threadId, block * (threadId - 1) + downLength);

                                               downloader.saveLogFile();

                                               downloader.append(offset);

                                               int spare = block-downLength;//求剩下的字节数

                                               if(spare < max) max = (int) spare;

                                     }

                                     saveFile.close();

                                     inStream.close();                   

                                     print("线程 " + this.threadId + "完成下载 ");

                                     this.finish = true;

                                     this.interrupt();

                            } catch (Exception e) {

                                     this.downLength = -1;

                                     print("线程"+ 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;

         }

}

11.DBOpenHelper

package com.changcheng.download.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 = 2;

        

         public DBOpenHelper(Context context) {

                   super(context, DBNAME, null, VERSION);

         }

        

         @Override

         public void onCreate(SQLiteDatabase db) {

                   db.execSQL("CREATE TABLE IF NOT EXISTS filedown (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER, position INTEGER)");

         }

 

         @Override

         public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

                   db.execSQL("DROP TABLE IF EXISTS filedown");

                   onCreate(db);

         }

}