java - 如何同步从不同来源（设备缓存、Web 服务器和 sqlite 数据库）获取数据？

Question

新年快乐！我正在学习使用 java 进行 android 开发，我首先按照本教程使用架构组件创建我的第一个应用程序： 应用程序架构指南

我对android 架构设计和其他基本的东西有很好的理解。但是，我在处理后台任务时仍然存在问题，因为有许多类提供多线程，例如：Executor、IntentService和asynctask ..

我的代码：

• 存储库类：

  public class MovieRpository  {
  private IWebService m_webService;
  private Movie _movie;
  private AppExecuters m_executers;
  
  private MovieRpository(AppExecuters executers, TMDB webService){
     this.m_executers = executers;
     this.m_webService = webService;
  }
  
   private static MovieRpository m_singleInstance;
  
   public static MovieRpository getInstance(){
      if(m_singleInstance == null){
           m_singleInstance = new 
   MovieRpository(AppExecuters.getInstance(), new TMDB(new JsonParser<Movie>()));
  }
  return  m_singleInstance;
  }
  
   public LiveData<Movie> getMovie( String movieId){
     final MutableLiveData<Movie> _liveDataMovie = new MutableLiveData<Movie>();
     m_executers.networkIO().execute(()->{
         _movie =(Movie)m_webService.getObject(movieId);});
     _liveDataMovie.setValue(_movie);
     return _liveDataMovie;
    }
   }
  

我的问题 ：

在存储库类中，当我在由m_executers.networkIO() 创建的第二个线程内使用调试器时， _movie在网络线程内有一个值。但是，它在执行方法之外始终为 null。

我的其余代码：

- IWebService 接口

  public interface IWebService<T> {
    public T getObject(String url);
  }

• 数据库：

  public class TMDB implements IWebService<Movie> {
     private JsonParser<Movie> m_jsonParser;
     private Movie _movie;
     public TMDB(JsonParser<Movie> jsonParser){
     m_jsonParser = jsonParser;
  }
  @Override
  public Movie getObject(String url) {
  
    try {
        HttpURLConnection _connection = (HttpURLConnection) (new URL(url)).openConnection();
        _connection.setRequestMethod(Settings.CONNECTION_GET_METHOD);
        _connection.setConnectTimeout(Settings.CONNECTION_TIMEOUT);
        _connection.setReadTimeout(Settings.DATA_READ_TIMEOUT);
        _connection.connect();
        InputStreamReader _streamReader = new InputStreamReader(_connection.getInputStream());
        BufferedReader _bufferedReader = new BufferedReader(_streamReader);
        StringBuilder _data = new StringBuilder();
        String _line;
        while((_line = _bufferedReader.readLine()) != null ){
            _data.append(_line);
        }
        _bufferedReader.close();
        _streamReader.close();
  
         Gson _gson = new Gson();
        _movie = _gson.fromJson(_data.toString(), Movie.class);
  
    }
    catch(MalformedURLException e) {
        e.printStackTrace();
    }
    catch(IOException e){
        e.printStackTrace();
    }
    return _movie;
    }
  }
  

• 用于管理线程的 AppExecuters 单例类：

  public class AppExecuters {
  private static AppExecuters m_singltonInstance;
  private Executor m_NetworkIO;
  private Executor m_diskIO;
  private Executor m_mainThread;
  private static final Object LOCK = new Object();
  
  private AppExecuters(Executor diskThread, Executor networkThread, Executor mainThread){
      this.m_diskIO = diskThread;
      this.m_mainThread = mainThread;
      this.m_NetworkIO = networkThread;
  }
  public static AppExecuters getInstance(){
      if(m_singltonInstance == null){
          // In-order to make the singleton instance synchronized between all threads.
          synchronized (LOCK){
              m_singltonInstance = new AppExecuters(Executors.newSingleThreadExecutor(), Executors.newFixedThreadPool(3), new MainThread());
          }
      }
      return m_singltonInstance;
  }
  
  public  Executor networkIO(){
      return m_NetworkIO;
  }
  public  Executor diskIO(){
      return m_diskIO;
  }
  public  Executor mainThread(){
      return m_mainThread;
  }
  
  private static class MainThread implements Executor{
      private Handler mainThreadHandler = new Handler(Looper.getMainLooper());
      @Override
      public void execute(Runnable command) {
          mainThreadHandler.post(command);
      }
  }
  

  }

• 我还需要知道在这种情况下管理线程的最佳实践。

标签： javaandroidmultithreadingexecutor