Android下使用Http协议实现多线程断点续传下载

0.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();

    RandomAccessFilefile = 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

    代码如下：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开始写入数据。

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

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

 

1.多线程下载的核心代码示例

public class MulThreadDownload
{
    /**
     * 多线程下载
     * @param args
     */
    public static void main(String[] args)
    {
        String path = "http://net.hoo.com/QQWubiSetup.exe";
        try
        {
            new MulThreadDownload().download(path, 3);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
    /**
     * 从路径中获取文件名称
     * @param path 下载路径
     * @return
     */
    public static String getFilename(String path)
    {
        return path.substring(path.lastIndexOf('/')+1);
    }
    /**
     * 下载文件
     * @param path 下载路径
     * @param threadsize 线程数
     */
    public void download(String path, int threadsize) throws Exception
    {
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection)url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(5 * 1000);
        //获取要下载的文件的长度
        int filelength = conn.getContentLength();
        //从路径中获取文件名称
        String filename = getFilename(path);
        File saveFile = new File(filename);
        RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");
        //设置本地文件的长度和下载文件相同
        accessFile.setLength(filelength);
        accessFile.close();
        //计算每条线程下载的数据长度
        int block = filelength%threadsize==0? filelength/threadsize : filelength/threadsize+1;
        for(int threadid=0 ; threadid < threadsize ; threadid++){
            new DownloadThread(url, saveFile, block, threadid).start();
        }
    }

    private final class DownloadThread extends Thread
    {
        private URL url;
        private File saveFile;
        private int block;//每条线程下载的数据长度
        private int threadid;//线程id
        public DownloadThread(URL url, File saveFile, int block, int threadid)
        {
            this.url = url;
            this.saveFile = saveFile;
            this.block = block;
            this.threadid = threadid;
        }
        @Override
        public void run()
        {
            //计算开始位置公式：线程id*每条线程下载的数据长度= ？
            //计算结束位置公式：（线程id +1）*每条线程下载的数据长度-1 =?
            int startposition = threadid * block;
            int endposition = (threadid + 1 ) * block - 1;
            try
            {
                RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");
                //设置从什么位置开始写入数据
                accessFile.seek(startposition);
                HttpURLConnection conn = (HttpURLConnection)url.openConnection();
                conn.setRequestMethod("GET");
                conn.setConnectTimeout(5 * 1000);
                conn.setRequestProperty("Range", "bytes="+ startposition+ "-"+ endposition);
                InputStream inStream = conn.getInputStream();
                byte[] buffer = new byte[1024];
                int len = 0;
                while( (len=inStream.read(buffer)) != -1 )
                {
                    accessFile.write(buffer, 0, len);
                }
                inStream.close();
                accessFile.close();
                System.out.println("线程id:"+ threadid+ "下载完成");
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
    }
}

 

 

2.多线程断点下载功能，这里把断点数据保存到数据库中：注意代码注释的理解

(0)主Activity，关键点使用Handler更新进度条与开启线程下载避免ANR

若不使用Handler却要立即更新进度条数据，可使用：

//resultView.invalidate(); UI线程中立即更新进度条方法

//resultView.postInvalidate(); 非UI线程中立即更新进度条方法

 

/**
 * 注意这里的设计思路，UI线程与参数保存问题，避免ANR问题，UI控件的显示
 * @author kay
 *
 */
public class DownloadActivity extends Activity
{
    private EditText downloadpathText;
    private TextView resultView;
    private ProgressBar progressBar;

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        downloadpathText = (EditText) this.findViewById(R.id.downloadpath);
        progressBar = (ProgressBar) this.findViewById(R.id.downloadbar);
        resultView = (TextView) this.findViewById(R.id.result);
        Button button = (Button) this.findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                //取得下载路径
                String path = downloadpathText.getText().toString();
                //判断SDCard是否存在
                if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))
                {
                    //下载操作
                    download(path, Environment.getExternalStorageDirectory());
                }
                else
                {
                    Toast.makeText(DownloadActivity.this, R.string.sdcarderror, 1).show();
                }
            }
        });
    }
    //主线程(UI线程)
    //业务逻辑正确，但是该程序运行的时候有问题(可能出现ANR问题)
    //对于显示控件的界面更新只是由UI线程负责，如果是在非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
    /**
     * 参数类型：因为启动一个线程还需要使用到上面方法的参数，而主方法启动后很快就会销毁，
     * 那么使用Final可以解决参数丢失的问题
     * path 注意是Final类型
     * savedir 注意是Final类型
     */
    private void download(final String path, final File savedir)
    {
        //这里开启一个线程避免ANR错误
        new Thread(new Runnable()
        {
            @Override
            public void run()
            {
                FileDownloader loader = new FileDownloader(DownloadActivity.this, path, savedir, 3);
                //设置进度条的最大刻度为文件的长度
                progressBar.setMax(loader.getFileSize());
                try
                {
                    loader.download(new DownloadProgressListener()
                    {
                        /**
                         * 注意这里的设计，显示进度条数据需要使用Handler来处理
                         * 因为非UI线程更新后的数据不能被刷新
                         */
                        @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();
                            //设置消息标签
                            msg.what = 1;
                            msg.getData().putInt("size", size);
                            //使用Handler对象发送消息
                            handler.sendMessage(msg);
                        }
                    });
                }
                catch (Exception e)
                {
                    //发送一个空消息到消息队列
                    handler.obtainMessage(-1).sendToTarget();
                    /**
                     *  或者使用下面的方法发送一个空消息
                     *  Message msg = new Message();
                     *  msg.what = 1;
                     *  handler.sendMessage(msg);
                     */
                }
            }
        }).start();
    }


    /**Handler原理：当Handler被创建时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()
    {
        //重写Handler里面的handleMessage方法处理消息
        @Override
        public void handleMessage(Message msg)
        {
            switch (msg.what)
            {
                case 1:
                    //进度条显示
                    progressBar.setProgress(msg.getData().getInt("size"));
                    float num = (float)progressBar.getProgress()/(float)progressBar.getMax();
                    int result = (int)(num*100);
                    //resultView.invalidate(); UI线程中立即更新进度条方法
                    //resultView.postInvalidate(); 非UI线程中立即更新进度条方法
                    resultView.setText(result+ "%");
                    //判断是否下载成功
                    if(progressBar.getProgress()==progressBar.getMax())
                    {
                        Toast.makeText(DownloadActivity.this, R.string.success, 1).show();
                    }
                    break;
                case -1:
                    Toast.makeText(DownloadActivity.this, R.string.error, 1).show();
                    break;
            }
        }
    };

}

 

(1)下载类：

注意计算每条线程的下载长度与下载起始位置的方法

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;
    //下载文件长度
    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()
    {
        //未下载完成
        if(downLength < block)
        {
            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");
                //下载开始位置：线程id*每条线程下载的数据长度 = ?
                int startPos = block * (threadId - 1) + downLength;
                //下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?
                int endPos = block * threadId -1;
                //设置获取实体数据的范围
                http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);
                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");
                //标记是否完成
                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;
    }
}

 

文件下载器，使用

/**
 * 文件下载器,使用这个类的方法如下示例：
 * 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);
    }
    /**
     * 文件下载构造器
     * @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];
            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)
            {
                //根据响应获取文件大小
                this.fileSize = conn.getContentLength();
                if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");
                //获取文件名称
                String filename = getFileName(conn);
                //构建保存文件
                this.saveFile = new File(fileSaveDir, filename);
                //获取下载记录
                Map<Integer, Integer> logdata = fileService.getData(downloadUrl);
                //如果存在下载记录
                if(logdata.size()>0)
                {
                    //把各条线程已经下载的数据长度放入data中
                    for(Map.Entry<Integer, Integer> entry : logdata.entrySet())
                        data.put(entry.getKey(), entry.getValue());
                }
                //下面计算所有线程已经下载的数据长度
                if(this.data.size()==this.threads.length)
                {
                    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
        {
            //创建本地文件
            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++)
                {
                    //初始化每条线程已经下载的数据长度为0
                    this.data.put(i+1, 0);
                }
            }
            //开启线程进行下载
            for (int i = 0; i < this.threads.length; i++)
            {
                int downLength = this.data.get(i+1);
                //判断线程是否已经完成下载,否则继续下载
                if(downLength < this.block && this.downloadSize<this.fileSize)
                {
                    this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
                    this.threads[i].setPriority(7);//可删除这条
                    this.threads[i].start();
                }
                else
                {
                    this.threads[i] = null;
                }
            }
            this.fileService.save(this.downloadUrl, this.data);
            //下载未完成
            boolean notFinish = true;
            // 循环判断所有线程是否完成下载
            while (notFinish)
            {
                Thread.sleep(900);
                //假定全部线程下载完成
                notFinish = false;
                for (int i = 0; i < this.threads.length; i++)
                {
                    //如果发现线程未完成下载
                    if (this.threads[i] != null && !this.threads[i].isFinish())
                    {
                        //设置标志为下载没有完成
                        notFinish = true;
                        //如果下载失败,再重新下载
                        if(this.threads[i].getDownLength() == -1)
                        {
                            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();
                        }
                    }
                }
                //通知目前已经下载完成的数据长度
                if(listener!=null) listener.onDownloadSize(this.downloadSize);
            }
            //删除数据库中下载信息
            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);
    }
}

 

public interface DownloadProgressListener
{
    public void onDownloadSize(int size);
}

 

(2)文件操作，断点数据库存储

public class DBOpenHelper extends SQLiteOpenHelper
{
    private static final String DBNAME = "itcast.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);
    }
}

 

/**
 * 文件下载业务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();
    }
}