Android实现多线程断点下载

implementation 'com.qw.download:download:1.0.0-alpha01'

public class MyApplication extends Application{
    @Override
    public void onCreate() {
        super.onCreate();
        //初始化下载组件(可在子线程中做)
        DownloadManager.init(this);
    }    
}

public class DownloadManager {
    private static DownloadManager mInstance;
    private final Context context;
    
    private DownloadManager(Context context) {}
    //初始化组件
    public static void init(Context context) {}
    //开启下载
    public static void add(DownloadEntry entry) {}  
    //暂停下载
    public static void pause(DownloadEntry entry) {}    
    //暂停所有任务
    public static void pauseAll() {}
    //恢复下载
    public static void resume(DownloadEntry entry) {}   
    //恢复所有任务
    public static void recoverAll() {}
}

private DownloadWatcher watcher = new DownloadWatcher() {
    @Override
    protected void onDataChanged(DownloadEntiry entry) {
	    //这里监听下载的实时信息
        mDownloadInfoLabel.setText(entry.toString());
        Log.e("MainActivity", entry.toString());
    }
};

@Override
protected void onResume() {
    super.onResume();
    //注册观察者
    DownloadManager.addObserver(watcher);
}

@Override
protected void onPause() {
    super.onPause();
    //移除观察者
    DownloadManager.removeObserver(watcher);
}

public class DownloadEntry implements Serializable {
    public String id;//下载的唯一标识
    public String url;//下载文件的url地址
    public boolean isSupportRange;//是否支持断点续传
    public long contentLength;//文件长度
    public long currentLength;//已下载文件长度
    public State state;//任务状态
    public HashMap<Integer, Long> ranges;//存储每个线程下载开始区块
    public int speed;//下载速度 单位s
}

public enum State {
    IDLE,//空闲
    CONNECT,//连接中(用户预取文件信息)
    ING,//下载中
    PAUSED,//已暂停
    CANCELLED,//已取消
    ERROR,//错误
    DONE,//完成
    WAIT//等待
}

public void addDownload(String id,String url){
    //id为任务的一个唯一标识，url为文件地址
    DownloadEntry entry = DownloadEntry.obtain(id,url)
    //添加一个下载任务
    DownloadManager.add(entry)    
}

public void pauseDownload(DownloadEntry entry){
    //添加一个下载任务
    DownloadManager.pause(entry)    
}

public void resumeDownload(DownloadEntry entry){
    //添加一个下载任务
    DownloadManager.resume(entry)    
}

public void pauseAll(DownloadEntry entry){
    //添加一个下载任务
    DownloadManager.resume(entry)    
}

public void recoverAll(DownloadEntry entry){
    //添加一个下载任务
    DownloadManager.recoverAll(entry)    
}

public class ApkEntry {
    public String id;//包id
    public String cover;//apk 图标
    public String name;//apk 名称
    public String url;//apk 下载地址
    public long length;//apk 大小

    public String id() {
        if (TextUtils.isEmpty(id)) {
            //如果服务端没有返回唯一标记则用url的md5值作为下载唯一标识
            id = FileUtilities.getMd5FileName(url);
        }
        return id;
    }
}

public void downloadApk(ApkEntry apkEntry){
    //1、先check当前apk是否在下载
    DownloadEntry entry = DownloadManager.findById(apkEntry.id())
    if(entry==null || entry.state==State.PAUSED || entry.state==State.ERROR || entry.state==State.CANCELLED){
        //这四种情况：没有下载任务 || 任务是暂停 || 下载失败 || 任务已被取消
        DownloadManager.add(entry)
    }
}

public void pauseDownloadApk(ApkEntry apkEntry){
    //1、先check当前apk是否在下载任务中
    DownloadEntry entry = DownloadManager.findById(apkEntry.id())
    if(entry!=null){
        DownloadManager.pause(entry)
    }
}