Android多線程斷點續傳

我們編寫的是Andorid的HTTP協議多線程斷點下載應用程序。直接使用單線程下載HTTP文件對我們來說是一件非常簡單的事。那麼，多線程斷點需要什麼功能？

1.多線程下載，

2.支持斷點。

使用多線程的好處：使用多線程下載會提升文件下載的速度。那麼多線程下載文件的過程是： (1)首先獲得下載文件的長度，然後設置本地文件的長度。

      HttpURLConnection.getContentLength();//獲取下載文件的長度
      RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rwd");
          file.setLength(filesize);//設置本地文件的長度

(2)根據文件長度和線程數計算每條線程下載的數據長度和下載位置。

如：文件的長度為6M，線程數為3，那麼，每條線程下載的數據長度為2M，每條線程開始下載的位置如下圖所示。

例如10M大小，使用3個線程來下載，

線程下載的數據長度 (10%3 == 0 ? 10/3:10/3+1) ,第1，2個線程下載長度是4M，第三個線程下載長度為2M

下載開始位置：線程id*每條線程下載的數據長度 = ?

下載結束位置：(線程id+1)*每條線程下載的數據長度-1=?

(3)使用Http的Range頭字段指定每條線程從文件的什麼位置開始下載，下載到什麼位置為止，

如：指定從文件的2M位置開始下載，下載到位置(4M-1byte)為止

代碼如下：

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

  (4)保存文件，使用RandomAccessFile類指定每條線程從本地文件的什麼位置開始寫入數據。

 RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");
 threadfile.seek(2097152);//從文件的什麼位置開始寫入數據

  程序結構如下圖所示：





 string.xml文件中代碼：

復制代碼

AndroidManifest.xml文件中代碼：

 MainActivity中代碼：

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;

    /**
     * 當Handler被創建會關聯到創建它的當前線程的消息隊列，該類用於往消息隊列發送消息
     * 消息隊列中的消息由當前線程內部進行處理
     */
    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();
                }
            }
        });
    }

      /**
       * 主線程(UI線程)
       * 對於顯示控件的界面更新只是由UI線程負責，如果是在非UI線程更新控件的屬性值，更新後的顯示界面不會反映到屏幕上
       * @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());//設置進度條的最大刻度為文件的長度

                try {
                    loader.download(new DownloadProgressListener() {
                        @Override
                        public void onDownloadSize(int size) {//實時獲知文件已經下載的數據長度
                            Message msg = new Message();
                            msg.what = 1;
                            msg.getData().putInt("size", size);
                            handler.sendMessage(msg);//發送消息
                        }
                    });
                } catch (Exception e) {
                    handler.obtainMessage(-1).sendToTarget();
                }
            }
        }).start();
    }
}  

DBOpenHelper中代碼：

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中代碼：

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);
    }

    /**
     * 獲取每條線程已經下載的文件長度
     * @param path
     * @return
     */
    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;
    }

    /**
     * 保存每條線程已經下載的文件長度
     * @param path
     * @param map
     */
    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();
    }

    /**
     * 實時更新每條線程已經下載的文件長度
     * @param path
     * @param map
     */
    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();
    }

    /**
     * 當文件下載完成後，刪除對應的下載記錄
     * @param path
     */
    public void delete(String path){
        SQLiteDatabase db = openHelper.getWritableDatabase();
        db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});
        db.close();
    }
}  

DownloadProgressListener中代碼：

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

FileDownloader中代碼：

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;    

    /* 已下載文件長度 */
    private int downloadSize = 0;

    /* 原始文件長度 */
    private int fileSize = 0;

    /* 線程數 */
    private DownloadThread[] threads;

    /* 本地保存文件 */
    private File saveFile;

    /* 緩存各線程下載的長度*/
    private Map data = new ConcurrentHashMap();

    /* 每條線程下載的長度 */
    private int block;

    /* 下載路徑  */
    private String downloadUrl;

    /**
     * 獲取線程數
     */
    public int getThreadSize() {
        return threads.length;
    }

    /**
     * 獲取文件大小
     * @return
     */
    public int getFileSize() {
        return fileSize;
    }

    /**
     * 累計已下載大小
     * @param size
     */
    protected synchronized void append(int size) {
        downloadSize += size;
    }

    /**
     * 更新指定線程最後下載的位置
     * @param threadId 線程id
     * @param pos 最後下載的位置
     */
    protected synchronized void update(int threadId, int pos) {
        this.data.put(threadId, pos);
        this.fileService.update(this.downloadUrl, this.data);
    }

    /**
     * 構建文件下載器
     * @param downloadUrl 下載路徑
     * @param fileSaveDir 文件保存目錄
     * @param threadNum 下載線程數
     */
    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();//根據響應獲取文件大小
                if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");

                String filename = getFileName(conn);//獲取文件名稱
                this.saveFile = new File(fileSaveDir, filename);//構建保存文件
                Map logdata = fileService.getData(downloadUrl);//獲取下載記錄

                if(logdata.size()>0){//如果存在下載記錄
                    for(Map.Entry entry : logdata.entrySet())
                        data.put(entry.getKey(), entry.getValue());//把各條線程已經下載的數據長度放入data中
                }

                if(this.data.size()==this.threads.length){//下面計算所有線程已經下載的數據長度
                    for (int i = 0; i < this.threads.length; i++) {
                        this.downloadSize += this.data.get(i+1);
                    }

                    print("已經下載的長度"+ this.downloadSize);
                }

                //計算每條線程下載的數據長度
                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");
        }
    }

    /**
     * 獲取文件名
     * @param conn
     * @return
     */
    private String getFileName(HttpURLConnection conn) {
        String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);

        if(filename==null || "".equals(filename.trim())){//如果獲取不到文件名稱
            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";//默認取一個文件名
        }

        return filename;
    }

    /**
     *  開始下載文件
     * @param listener 監聽下載數量的變化,如果不需要了解實時下載的數量,可以設置為null
     * @return 已下載文件大小
     * @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);//初始化每條線程已經下載的數據長度為0
                }
            }

            for (int i = 0; i < this.threads.length; i++) {//開啟線程進行下載
                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;
    }

    /**
     * 打印Http頭字段
     * @param http
     */
    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 中代碼：

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;

    /* 下載開始位置  */
    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){//未下載完成
            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;//開始位置
                int endPos = block * threadId -1;//結束位置
                http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//設置獲取實體數據的范圍
                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);
    }

    /**
     * 下載是否完成
     * @return
     */
    public boolean isFinish() {
        return finish;
    }

    /**
     * 已經下載的內容大小
     * @return 如果返回值為-1,代表下載失敗
     */
    public long getDownLength() {
        return downLength;
    }
}