安卓断点续传核心代码DownloadTask

来源：互联网发布：淘宝网蜜袋鼯购买编辑：程序博客网时间：2024/05/16 01:47
废话不多说。我们直接上代码。重点用注释已经写出来了。与传统的下载略有不同。
/** * 下载文件线程 * 从服务器获取需要下载的文件大小 */public class DownLoadTask extends Thread {    private FileInfo info;    private SQLiteDatabase db;    private DbHelper helper;//数据库帮助类    private int finished = 0;//当前已下载完成的进度    private OnProgressListener listener;//进度回调监听    public DownLoadTask(FileInfo info, DbHelper helper, OnProgressListener listener) {        this.info = info;        this.helper = helper;        this.db = helper.getReadableDatabase();        this.listener = listener;        info.setDownLoading(true);    }    @Override    public void run() {        getLength();        HttpURLConnection connection = null;        RandomAccessFile rwd = null;        try {            URL url = new URL(info.getUrl());            connection = (HttpURLConnection) url.openConnection();            connection.setRequestMethod("GET");            connection.setConnectTimeout(3000);            //从上次下载完成的地方下载            int start = info.getFinished();            //设置下载位置(从服务器上取要下载文件的某一段)            connection.setRequestProperty("Range", "bytes=" + start + "-" + info.getLength());//设置下载范围            //设置文件写入位置            File file = new File(DownLoaderManger.FILE_PATH, info.getFileName());            rwd = new RandomAccessFile(file, "rwd");            //从文件的某一位置开始写入            rwd.seek(start);            finished += info.getFinished();            if (connection.getResponseCode() == 206) {//文件部分下载，返回码为206                InputStream is = connection.getInputStream();                byte[] buffer = new byte[1024 * 4];                int len;                while ((len = is.read(buffer)) != -1) {                    //写入文件                    rwd.write(buffer, 0, len);                    finished += len;                    info.setFinished(finished);                    //更新界面显示                    Message msg = new Message();                    msg.what = 0x123;                    msg.arg1 = info.getLength();                    msg.arg2 = info.getFinished();                    handler.sendMessage(msg);                    //停止下载                    if (info.isStop()) {                        info.setDownLoading(false);                        //保存此次下载的进度                        helper.updateData(db, info);                        db.close();                        return;                    }                }                //下载完成                info.setDownLoading(false);                helper.updateData(db, info);                db.close();            }        } catch (Exception e) {            e.printStackTrace();        } finally {            if (connection != null) {                connection.disconnect();            }            try {                if (rwd != null) {                    rwd.close();                }            } catch (IOException e) {                e.printStackTrace();            }        }    }    /**     * 首先开启一个线程去获取要下载文件的大小（长度）     */    private void getLength() {        HttpURLConnection connection = null;        try {            //连接网络            URL url = new URL(info.getUrl());            connection = (HttpURLConnection) url.openConnection();            connection.setRequestMethod("GET");            connection.setConnectTimeout(3000);            int length = -1;            if (connection.getResponseCode() == 200) {//网络连接成功                //获得文件长度                length = connection.getContentLength();            }            if (length <= 0) {                //连接失败                return;            }            //创建文件保存路径            File dir = new File(DownLoaderManger.FILE_PATH);            if (!dir.exists()) {                dir.mkdirs();            }            info.setLength(length);        } catch (Exception e) {            e.printStackTrace();        } finally {            //释放资源            try {                if (connection != null) {                    connection.disconnect();                }            } catch (Exception e) {                e.printStackTrace();            }        }    }    /**     * 更新进度     */    private Handler handler = new Handler() {        @Override        public void handleMessage(Message msg) {            switch (msg.what) {                case 0x123:                    if (listener != null) {                        listener.updateProgress(msg.arg1, msg.arg2);                    }                    break;            }        }    };}
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