文件下载实现进度条与端点续传

下载线程：

public class MyThread extends Thread{
        @RequiresApi(api = Build.VERSION_CODES.N)
        @Override
        public void run() {
            try {
                URL url = new URL("https://media.w3.org/2010/05/sintel/trailer.mp4");
                HttpURLConnection connection = (HttpURLConnection)url.openConnection();
                connection.setRequestMethod("GET");
                connection.setDoInput(true);
                connection.setDoOutput(true);
                //指定下载范围
                connection.setRequestProperty("Range","bytes="+start+"-"+end);
                //由于是范围访问 无法获取到总长度 只会获取到范围内的最大长度 所以需要单开线程获取
                Log.e("###","判断");
                if(connection.getResponseCode() == 206){
                    Log.e("###","进来了");
                    int length = connection.getContentLength();//获取文件的总长度
                    //存文件的位置
                    String path = Environment.getExternalStorageDirectory().getAbsolutePath()+"/"+"video"+".mp4";
                    RandomAccessFile randomAccessFile = new RandomAccessFile(path,"rw");
                    Log.e("START###",start+"");
                    randomAccessFile.seek(start);
                    //获取流
                    InputStream is = connection.getInputStream();
                    byte[] b = new byte[1024];
                    int len = -1;
                    while((len = is.read(b))!=-1&&flag){
                        Message m = new Message();
                        randomAccessFile.write(b,0,len);
                        sum+=len;
                        m.arg1 = sum;
                        m.what = 3;
                        handler.sendMessage(m);
                    }
                    Log.e("end###",end+"");
                    if(randomAccessFile != null){
                        randomAccessFile.close();
                    }
                    if(is != null){
                        is.close();
                    }

                    Message message = new Message();
                    if(flag){
                        message.what = 1;
                        start = end+1;
                        end += 1024*1024;
                    }else{
                        message.what = 0;
                        start = sum;
                    }
                    //发送Handler实现界面的更新
                    handler.sendMessage(message);
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

获取进度条最大值：

//需要开启一个单独的线程获取总长度
    public class PbThread extends Thread{
        @Override
        public void run() {
            URL url = null;
            try {
                url = new URL("https://media.w3.org/2010/05/sintel/trailer.mp4");
                HttpURLConnection connection = (HttpURLConnection)url.openConnection();
                int length = connection.getContentLength();
                Log.e("length###",length+"");
                Message message = new Message();
                message.what = 2;
                message.arg1 = length;
                //发送给主类设置总长度
                handler.sendMessage(message);
            } catch (Exception e) {
                e.printStackTrace();
            }

        }
    }

handler类方法重写：

Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if(msg.what == 1){

                new MyThread().start();
            }else if(msg.what == 0){
                Log.e("###pause","暂停");
            }else if(msg.what == 2){
                pb.setMax(msg.arg1);
            }else if(msg.what == 3){
                pb.setProgress(msg.arg1);
            }
        }
    };

主类：

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_baidu_cloud);
        initView();
    }

    private void initView() {
        findViewById(R.id.btn1).setOnClickListener(this);
        findViewById(R.id.pause).setOnClickListener(this);
        findViewById(R.id.again).setOnClickListener(this);
        pb = findViewById(R.id.pb);
    }

按钮监听方法：

@Override
    public void onClick(View v) {
        switch(v.getId()){
            case R.id.btn1:
                new MyThread().start();//开启下载线程
                new PbThread().start();//开启获取总长度线程
                break;
            case R.id.pause:
                flag = false;//暂停
                break;
            case R.id.again:
                flag = true;
                new MyThread().start();//继续
                break;
        }
    }