断点下载数据

public class MainActivity extends Activity {
    private EditText pathText;
    private TextView resultView;
    private Button downloadButton;
    private Button stopbutton;
    private ProgressBar progressBar;
    //hanlder的作用是用于往创建Hander对象所在的线程所绑定的消息队列发送消息
    private Handler handler = new UIHander();
    
    private final class UIHander extends Handler{//重写Handler中的handleMessage方法
        public void handleMessage(Message msg) {
            switch (msg.what) {//msg.what  Message的标记
            case 1:
                int size = msg.getData().getInt("size");//从消息的数据中取出其他线程存进的数据
                progressBar.setProgress(size);
                float num = (float)progressBar.getProgress() / (float)progressBar.getMax();
                int result = (int)(num * 100);
                resultView.setText(result+ "%");
                if(progressBar.getProgress() == progressBar.getMax()){
                    Toast.makeText(getApplicationContext(), R.string.success, 1).show();
                }
                break;

            case -1:
                Toast.makeText(getApplicationContext(), R.string.error, 1).show();
                break;
            }
        }
    }
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        pathText = (EditText) this.findViewById(R.id.path);
        resultView = (TextView) this.findViewById(R.id.resultView);
        downloadButton = (Button) this.findViewById(R.id.downloadbutton);
        stopbutton = (Button) this.findViewById(R.id.stopbutton);
        progressBar = (ProgressBar) this.findViewById(R.id.progressBar);
        ButtonClickListener listener = new ButtonClickListener();
        downloadButton.setOnClickListener(listener);
        stopbutton.setOnClickListener(listener);
    }
    
    private final class ButtonClickListener implements View.OnClickListener{
        public void onClick(View v) {
            switch (v.getId()) {
            case R.id.downloadbutton:
                String path = pathText.getText().toString();
                if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
                    File saveDir = Environment.getExternalStorageDirectory();
                    download(path, saveDir);
                }else{
                    Toast.makeText(getApplicationContext(), R.string.sdcarderror, 1).show();
                }
                downloadButton.setEnabled(false);
                stopbutton.setEnabled(true);
                break;

            case R.id.stopbutton:
                exit();
                downloadButton.setEnabled(true);
                stopbutton.setEnabled(false);
                break;
            }
        }
        /*
        由于用户的输入事件(点击button, 触摸屏幕....)是由主线程负责处理的，如果主线程处于工作状态，
        此时用户产生的输入事件如果没能在5秒内得到处理，系统就会报“应用无响应”错误。
        所以在主线程里不能执行一件比较耗时的工作，否则会因主线程阻塞而无法处理用户的输入事件，
        导致“应用无响应”错误的出现。耗时的工作应该在子线程里执行。
         */
        private DownloadTask task;
        /**
         * 退出下载
         */
        public void exit(){
            if(task!=null) task.exit();
        }
        private void download(String path, File saveDir) {//运行在主线程
            task = new DownloadTask(path, saveDir);
            new Thread(task).start();
        }
        
        
        /*
         * UI控件画面的重绘(更新)是由主线程负责处理的，如果在子线程中更新UI控件的值，更新后的值不会重绘到屏幕上
         * 一定要在主线程里更新UI控件的值，这样才能在屏幕上显示出来，不能在子线程中更新UI控件的值
         */
        private final class DownloadTask implements Runnable{
            private String path;
            private File saveDir;
            private FileDownloader loader;
            public DownloadTask(String path, File saveDir) {
                this.path = path;
                this.saveDir = saveDir;
            }
            /**
             * 退出下载
             */
            public void exit(){
                if(loader!=null) loader.exit();
            }
            
            public void run() {
                try {
                    loader = new FileDownloader(getApplicationContext(), path, saveDir, 3);
                    progressBar.setMax(loader.getFileSize());//设置进度条的最大刻度
                    loader.download(new DownloadProgressListener() {
                        public void onDownloadSize(int size) {
                            Message msg = new Message();
                            msg.what = 1;
                            msg.getData().putInt("size", size);
                            handler.sendMessage(msg);//向创建handler对象的线程发送消息
                        }
                    });
                } catch (Exception e) {
                    e.printStackTrace();
                    handler.sendMessage(handler.obtainMessage(-1));
                }
            }            
        }
    }
    
    
}

/**
 * 文件下载器
 * 
    try {
        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
        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;  //上下文对象
    private FileService fileService;
    /* 停止下载 */
    private boolean exit;
    /* 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;
    }
    /**
     * 退出下载
     */
    public void exit(){
        this.exit = true;
    }
    public boolean getExit(){
        return this.exit;
    }
    /**
     * 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, threadId, pos);
    }
    /**
     * 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; //下载地址
            fileService = new FileService(this.context);
            URL url = new URL(this.downloadUrl);  
            if(!fileSaveDir.exists()) fileSaveDir.mkdirs();//判断下载文件保存目录是否存在，不存在创建
            this.threads = new DownloadThread[threadNum];    //创建一个线程数组                
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            //设置头字段
            conn.setConnectTimeout(5*1000);
            conn.setRequestMethod("GET");
            conn.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
            conn.setRequestProperty("Accept-Language", "zh-CN");
            conn.setRequestProperty("Referer", downloadUrl); 
            conn.setRequestProperty("Charset", "UTF-8");
            conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
            conn.setRequestProperty("Connection", "Keep-Alive");
            conn.connect();
            printResponseHeader(conn);
            if (conn.getResponseCode()==200) {
                this.fileSize = conn.getContentLength();//根据响应获取文件大小
                if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");
                        
                String filename = getFileName(conn);//获取文件名称
                this.saveFile = new File(fileSaveDir, filename);//构建保存文件

                Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//获取每条线程已经下载的文件长度
                if(logdata.size()>0){//如果存在下载记录
                    for(Map.Entry<Integer, Integer> entry : logdata.entrySet())
                        data.put(entry.getKey(), entry.getValue());//把各条线程已经下载的数据长度放入data中
                }
                if(this.data.size()==this.threads.length){//下面计算所有线程已经下载的数据总长度
                    for (int i = 0; i < this.threads.length; i++) {
                        this.downloadSize += this.data.get(i+1);
                    }
                    print("已经下载的长度"+ this.downloadSize);
                }
                //计算每条线程下载的数据长度
                this.block = (this.fileSize % this.threads.length)==0? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1;
            }else{
                throw new RuntimeException("server no response ");
            }
        } catch (Exception e) {
            print(e.toString());
            throw new RuntimeException("don't connection this url");
        }
    }
    /**
     * 获取文件名
     */
    private String getFileName(HttpURLConnection conn) {
        String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);
        if(filename==null || "".equals(filename.trim())){//如果获取不到文件名称
            for (int i = 0;; i++) {
                String mine = conn.getHeaderField(i);
                if (mine == null) break;
                if("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())){
                    Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase());
                    if(m.find()) return m.group(1);
                }
            }
            filename = UUID.randomUUID()+ ".tmp";//默认取一个文件名
        }
        return filename;
    }
    
    /**
     *  开始下载文件
     * @param listener 监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null
     * @return 已下载文件大小
     * @throws Exception
     */
    public int download(DownloadProgressListener listener) throws Exception{
        try {
            RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");
            if(this.fileSize>0) randOut.setLength(this.fileSize);
            randOut.close();
            URL url = new URL(this.downloadUrl);
            if(this.data.size() != this.threads.length){//如果原先未曾下载或者原先的下载线程数与现在的线程数不一致
                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
                }
                this.downloadSize = 0;
            }
            for (int i = 0; i < this.threads.length; i++) {//开启线程进行下载
                int downLength = this.data.get(i+1);
                if(downLength < this.block && this.downloadSize<this.fileSize){//判断线程是否已经完成下载,否则继续下载    
                    this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
                    this.threads[i].setPriority(7);
                    this.threads[i].start();
                }else{
                    this.threads[i] = null;
                }
            }
            fileService.delete(this.downloadUrl);//如果存在下载记录，删除它们，然后重新添加
            fileService.save(this.downloadUrl, this.data);
            boolean notFinish = true;//下载未完成
            while (notFinish) {// 循环判断所有线程是否完成下载
                Thread.sleep(900);
                notFinish = false;//假定全部线程下载完成
                for (int i = 0; i < this.threads.length; i++){
                    if (this.threads[i] != null && !this.threads[i].isFinish()) {//如果发现线程未完成下载
                        notFinish = true;//设置标志为下载没有完成
                        if(this.threads[i].getDownLength() == -1){//如果下载失败,再重新下载
                            this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
                            this.threads[i].setPriority(7);
                            this.threads[i].start();
                        }
                    }
                }                
                if(listener!=null) listener.onDownloadSize(this.downloadSize);//通知目前已经下载完成的数据长度
            }
            if(downloadSize == this.fileSize) fileService.delete(this.downloadUrl);//下载完成删除记录
        } catch (Exception e) {
            print(e.toString());
            throw new Exception("file download error");
        }
        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 class DownloadThread extends Thread {
    private static final String TAG = "DownloadThread";
    private File saveFile;
    private URL downUrl;
    private int block;
    /* 下载开始位置  */
    private int threadId = -1;    
    private int downLength;
    private boolean finish = false;
    private FileDownloader downloader;

    public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downLength, int threadId) {
        this.downUrl = downUrl;
        this.saveFile = saveFile;
        this.block = block;
        this.downloader = downloader;
        this.threadId = threadId;
        this.downLength = downLength;
    }
    
    @Override
    public void run() {
        if(downLength < block){//未下载完成
            try {
                HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();
                http.setConnectTimeout(5 * 1000);
                http.setRequestMethod("GET");
                http.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
                http.setRequestProperty("Accept-Language", "zh-CN");
                http.setRequestProperty("Referer", downUrl.toString()); 
                http.setRequestProperty("Charset", "UTF-8");
                int startPos = block * (threadId - 1) + downLength;//开始位置
                int endPos = block * threadId -1;//结束位置
                http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//设置获取实体数据的范围
                http.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
                http.setRequestProperty("Connection", "Keep-Alive");
                
                InputStream inStream = http.getInputStream();
                byte[] buffer = new byte[1024];
                int offset = 0;
                print("Thread " + this.threadId + " start download from position "+ startPos);
                RandomAccessFile threadfile = new RandomAccessFile(this.saveFile, "rwd");
                threadfile.seek(startPos);
                while (!downloader.getExit() && (offset = inStream.read(buffer, 0, 1024)) != -1) {
                    threadfile.write(buffer, 0, offset);
                    downLength += offset;
                    downloader.update(this.threadId, downLength);
                    downloader.append(offset);
                }
                threadfile.close();
                inStream.close();
                print("Thread " + this.threadId + " download finish");
                this.finish = true;
            } catch (Exception e) {
                this.downLength = -1;
                print("Thread "+ this.threadId+ ":"+ e);
            }
        }
    }
    private static void print(String msg){
        Log.i(TAG, msg);
    }
    /**
     * 下载是否完成
     * @return
     */
    public boolean isFinish() {
        return finish;
    }
    /**
     * 已经下载的内容大小
     * @return 如果返回值为-1,代表下载失败
     */
    public long getDownLength() {
        return downLength;
    }
}

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

/**
 * 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, int threadId, int pos){
        SQLiteDatabase db = openHelper.getWritableDatabase();
        db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?",
                new Object[]{pos, path, threadId});
        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();
    }
    
}

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);
    }

}

 <ProgressBar
     android:layout_width="fill_parent"
     android:layout_height="18dp"
     style="?android:attr/progressBarStyleHorizontal" //使用系统中的横向滚动条
     android:id="@+id/progressBar"
    />