Android实现网络多线程断点续传下载

 本演示样例介绍在Android平台下通过HTTP协议实现断点续传下载。

 我们编写的是Andorid的HTTP协议多线程断点下载应用程序。直接使用单线程下载HTTP文件对我们来说是一件很easy的事。那么，多线程断点须要什么功能？

1.多线程下载，

2.支持断点。

使用多线程的优点：使用多线程下载会提升文件下载的速度。

那么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)依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，每条线程開始下载的位置例如以下图所看到的。

 

   比如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

        下载開始位置：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開始下载，下载到什么位置为止，

        如：指定从文件的2M位置開始下载。下载到位置(4M-1byte)为止

           代码例如以下：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開始写入数据。

RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");

threadfile.seek(2097152);//从文件的什么位置開始写入数据

  程序结构例如以下图所看到的：

string.xml文件里代码：

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

<resources>
    <string name="hello">Hello World, MainActivity!</string>
    <string name="app_name">Android网络多线程断点下载</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>
    <string name="success">下载完毕</string>
    <string name="error">下载失败</string>
</resources>

main.xml文件里代码：

<?

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:id="@+id/path"
        android:text="http://www.winrar.com.cn/download/wrar380sc.exe"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content">
    </EditText>
    <!-- 下载button -->
    <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" />
    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:id="@+id/resultView" />
    </LinearLayout>

AndroidManifest.xml文件里代码：

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

<manifest xmlns:android="http://schemas.android.com/apk/res/android"      package="com.android.downloader"      android:versionCode="1"      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="8" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MainActivity"
                  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>
   
    <!-- 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"/>
   
    <!-- 訪问internet权限 -->
    <uses-permission android:name="android.permission.INTERNET"/>

</manifest>

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;

    

    /**

     * 当Handler被创建会关联到创建它的当前线程的消息队列，该类用于往消息队列发送消息

     * 消息队列中的消息由当前线程内部进行处理

     */

    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();

                }

            }

        });

    }

    

      /**

       * 主线程(UI线程)

       * 对于显示控件的界面更新仅仅是由UI线程负责，假设是在非UI线程更新控件的属性值，更新后的显示界面不会反映到屏幕上

       * @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());//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);

    }

    

    /**

     * 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();

    }

    

    /**

     * 当文件下载完毕后。删除相应的下载记录

     * @param path

     */

    public void delete(String path){

        SQLiteDatabase db = openHelper.getWritableDatabase();

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

        db.close();

    }

}

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;    

    

    /* 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 文件保存文件夹

     * @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];                    

            

            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();//依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

                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

                

                if(logdata.size()>0){//假设存在下载记录

                    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){//以下计算全部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");

        }

    }

    

    /**

     * 获取文件名称

     * @param conn

     * @return

     */

    private String getFileName(HttpURLConnection conn) {

        String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);

        

        if(filename==null || "".equals(filename.trim())){//假设获取不到文件名

            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";//默认取一个文件名称

        }

        

        return filename;

    }

    

    /**

     *  開始下载文件

     * @param listener 监听下载数量的变化,假设不须要了解实时下载的数量,能够设置为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);

            

            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){//推断线程是否已经完毕下载,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;//下载未完毕

            

            while (notFinish) {// 循环推断全部线程是否完毕下载

                Thread.sleep(900);

                notFinish = false;//假定所有线程下载完毕

                

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

                    if (this.threads[i] !=
null && !this.threads[i].isFinish()) {//假设发现线程未完毕下载

                        notFinish = true;//设置标志为下载没有完毕

                        

                        if(this.threads[i].getDownLength() == -1){//假设下载失败,再又一次下载

                            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);//通知眼下已经下载完毕的数据长度

            }

            

            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 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;

    

    /* 下载開始位置  
*/

    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){//未下载完毕

            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;//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);

    }

    

    /**

     * 下载是否完毕

     * @return

     */

    public boolean isFinish() {

        return finish;

    }

    

    /**

     * 已经下载的内容大小

     * @return 假设返回值为-1,代表下载失败

     */

    public long getDownLength() {

        return downLength;

    }

}

执行效果例如以下：

最后，希望转载的朋友可以尊重作者的劳动成果，加上转载地址：http://www.cnblogs.com/hanyonglu/archive/2012/02/20/2358801.html 谢谢。

演示样例源代码：点击下载

完成。^_^

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