Android 多线程下载和断点续传

需要知识

1. Http请求头 Range

读取网络下载文件的指定范围的字节

2. RandomAccessFile

RandomAccessFile支持跳到文件任意位置读写数据

3. 记得添加和开启权限

4. 高版本无法连接http网络解决方案

具体代码

1.开始和暂停下载

// 开始下载
    private void startDown(){
        Intent intent = new Intent(getActivity(), DownService.class);
        intent.setAction(DownService.ACTION_START);
        intent.putExtra("downUrl","https://download.java.net/openjdk/jdk9/ri/openjdk-9_src.zip");
        getActivity().startService(intent);
    }
// 暂停下载
    private void stopDown(){
        Intent intent = new Intent(getActivity(),DownService.class);
        intent.setAction(DownService.ACTIOn_STOP);
        getActivity().startService(intent);
    }

2.开启下载服务

public class DownService extends Service {
    private static final String TAG = "DownService";
    public static final String ACTION_START = "ACTION_START";
    public static final String ACTIOn_STOP = "ACTION_PAUSE";
    public static final String DOWN_PATH = Environment.getExternalStorageDirectory().getAbsolutePath() + "/dahai/";
    public static final String DOWN_FILE_NAME = "aaa.zip";
    private String downUrl;
    private DownTask mDownTask;
    private int length;

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        String action = intent.getAction();

        if (action.equals(ACTION_START)) {
            downUrl = intent.getStringExtra("downUrl");
            new InitThread().start();
        } else if (action.equals(ACTIOn_STOP)) {
            Log.e(TAG,"停止下载");
            mDownTask.pause = true;
        }

        return super.onStartCommand(intent, flags, startId);
    }

    Handler handler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            Log.e("zhy","开始下载");
            if (mDownTask == null)
                mDownTask = new DownTask(new File(DOWN_PATH,DOWN_FILE_NAME),downUrl,length);
            mDownTask.startDown();
            return true;
        }
    });

    class InitThread extends Thread {
        HttpURLConnection connection;
        RandomAccessFile raf;

        @Override
        public void run() {
            try {
                URL url = new URL(downUrl);
                connection = (HttpURLConnection) url.openConnection();
                connection.setConnectTimeout(3000);
                if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
                    // 获取文件长度
                    length = connection.getContentLength();
                    Log.e("zhy","文件的长度 == " + length);
                }

                if (length < 0) {
                    return;
                }

                File dir = new File(DOWN_PATH);
                if (!dir.exists()) {
                    boolean mkdir = dir.mkdir();
                    Log.e("zhy","文件创建成功与否：" + mkdir);
                }
                Log.e("zhy",dir.getAbsolutePath());
                // 创建本地文件
                File file = new File(DOWN_PATH,DOWN_FILE_NAME);
                raf = new RandomAccessFile(file,"rwd");
                raf.setLength(length);

                handler.obtainMessage(1).sendToTarget();
            }catch(MalformedURLException e){
                e.printStackTrace();
                Log.e("zhy",e.toString());
            } catch (IOException e) {
                e.printStackTrace();
                Log.e("zhy",e.toString());
            }
        }
    }
}

3.具体下载控制代码

public class DownTask {
    private long startPos;
    private File downPath;
    private String downUrl;
    private long fileLength;
    // todo : 线程安全。。。。
    public boolean pause = false;

    public static ExecutorService executorService = Executors.newCachedThreadPool();
    List threadInfos = new ArrayList<>();
    private List mThreadList = null;

    public DownTask(File downPath,String downUrl,long fileLength) {
        this.downPath = downPath;
        this.downUrl = downUrl;
        this.fileLength = fileLength;
    }

    public void startDown() {
        Log.e("zhy","开启下载线程");
        pause = false;
        if (threadInfos.size() == 0) {
            long length = fileLength/3;
            for (int i = 0;i < 3;i++) {
                ThreadInfo threadInfo = new ThreadInfo(i,i * length,(i+1) * length -1,0);
                if (i + 1 == 3) {
                    threadInfo.setEnd(fileLength);
                }
                threadInfos.add(threadInfo);
            }
        }

        mThreadList = new ArrayList<>();
        for (ThreadInfo threadInfo : threadInfos) {
            DownThread t = new DownThread(threadInfo);
            executorService.execute(t);
            mThreadList.add(t);
        }

    }

    class DownThread extends Thread {
        private ThreadInfo threadInfo;
        private boolean isFinished;

        public DownThread(ThreadInfo threadInfo) {
            this.threadInfo = threadInfo;
        }

        @Override
        public void run() {
            InputStream is;
            RandomAccessFile raf;

            try {
                URL url = new URL(downUrl);
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                long start = threadInfo.getStart() + threadInfo.getFinished();
                urlConnection.setRequestProperty("Range","bytes=" + start + "-" + threadInfo.getEnd());
                raf = new RandomAccessFile(downPath, "rwd");
                raf.seek(startPos);

                if (urlConnection.getResponseCode() == HttpURLConnection.HTTP_PARTIAL) {
                    is = urlConnection.getInputStream();
                    byte[] buffer = new byte[4096];
                    int length = -1;
                    while ((length = is.read(buffer)) != -1) {
                        if (pause) {
                            // todo ：数据需要保存到本地。
                            return;
                        }

                        raf.write(buffer,0,length);
                        threadInfo.setFinished(threadInfo.getFinished() + length);
                        Log.e("zhy","线程" + threadInfo.getId() + "的下载进度 == " + threadInfo.getFinished());

                    }

                    // 标识线程执行完毕
                    isFinished = true;
                    // 检查下载任务是否完成
                    checkAllThreadFinished();
                    is.close();
                    raf.close();
                    urlConnection.disconnect();
                }
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void checkAllThreadFinished(){
        synchronized (this) {
            boolean allFinished = true;
            for (DownThread thread : mThreadList) {
                if (!thread.isFinished) {
                    allFinished = false;
                    break;
                }
            }
            if (allFinished) {
                Log.e("zhy","下载完成");
            }
        }

    }
}``