需要等待異步API回調，然後再從Java中的方法返回

Question

import java.util.concurrent.CountDownLatch; 

    import quickfix.Initiator; 


    public class UserSession { 
    private final CountDownLatch latch = new CountDownLatch(1); 

public String await() { 
     try { 
      System.out.println("waiting..."); 
      if (latch.await(5, TimeUnit.SECONDS)) 
       System.out.println("released!"); 
      else 
       System.out.println("timed out"); 
      return secret; 
     } catch (InterruptedException e) { 
      // TODO Auto-generated catch block 
      System.out.println(e.getMessage()); 
      e.printStackTrace(); 
     } 
     return null; 
    } 

    public void countdown(String s) { 
     System.out.println("In countdown: "+s+ ". Latch count: "+latch.getCount()); 
     secret = s; 
     latch.countDown(); 
     System.out.println("Latch count: "+latch.getCount()); 
    } 
    } 


    public class LogonHandler extends AbstractHandler { 

    public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response) 
     throws IOException, ServletException 
     { 
      Map<String,String[]> query = request.getParameterMap(); 

      if (query.containsKey("method")) { 
       if (query.get("method")[0].compareTo(method) == 0) { 
        baseRequest.setHandled(true); 
        response.getWriter().println(logon(query)); 
       } 
      } 
      else 
       baseRequest.setHandled(false); 
     } 

    private String logon(Map<String,String[]> query) { 
     if (query.containsKey("username") && query.containsKey("password") &&   query.containsKey("sendercompid")) { 

      app.mapUser(query.get("sendercompid")[0], new UserSession(query.get("username")[0], query.get("password")[0])); 

      SessionID session = new SessionID(new BeginString("FIX.4.4"), new SenderCompID(query.get("sendercompid")[0]), new TargetCompID("PARFX")); 

      try { 
       ThreadedSocketInitiator tsi = new ThreadedSocketInitiator(app, app.getFileStoreFactory(), settings, app.getLogFactory(), app.getMessageFactory()); 
       UserSession userSession = new UserSession(query.get("username")[0], query.get("password")[0]); 
       userSession.setInitiator(tsi); 

       tsi.start(); 
       return userSession.await(); 
      } catch (ConfigError e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
       return e.toString(); 
      } 
     } 
     return "fail"; 
    } 
    } 


public class QuickfixjApplication implements Application { 
    private Map<String,UserSession> users = new HashMap<String,UserSession>(); 

    public void mapUser(String s, UserSession u) { 
     users.put(s, u); 
    } 

    public void toAdmin(Message message, SessionID sessionId) { 

     try { 
      if (message.getHeader().getField(new StringField(MsgType.FIELD)).valueEquals(Logon.MSGTYPE)) { 
       UserSession user = users.get(sessionId.getSenderCompID()); 
       message.setField(new Username(user.getUsername())); 
       message.setField(new Password(user.getPassword())); 
      } 
     } catch (FieldNotFound e) { 
      e.printStackTrace(); 
     } 
    } 

    public void fromAdmin(Message message, SessionID sessionId) 
     throws FieldNotFound, IncorrectDataFormat, IncorrectTagValue, RejectLogon { 

     if (message.getHeader().getField(new StringField(MsgType.FIELD)).valueEquals(Logon.MSGTYPE)) { 
      System.out.println(message.toString()); 
      UserSession user = users.get(sessionId.getSenderCompID()); 
      user.countdown(message.toString()); 
     } 
    } 
} 

好的，我試過只在這裏包含最少量的代碼。有三個有趣的類，UserSession是Jetty處理程序和QuickFix/j應用程序之間的內部粘連。

LogonHandler收到HTTP登錄請求並嘗試將用戶登錄到QuickFix/j應用程序會話。

QuickFix/j正在向FIX服務器發送登錄消息，此登錄請求/響應是異步的。 HTTP登錄請求當然是同步的。因此，在我們從HTTP請求返回之前，我們必須等待來自FIX服務器的回覆。我使用CountDownLatch和此UserSession對象執行此操作。

當我創建QuickFix/j會話對象時，我還創建了一個UserSession對象並將它添加到映射中（發生在LogonHandler登錄方法中）。

QuickFix/j應用程序對象toAdmin（）和fromAdmin（）中有兩個回調。在fromAdmin（）中檢查消息是否是登錄響應，如果是，則調用UserSession的方法來倒計時。在調試代碼時，我看到fromAdmin（）方法被觸發，在映射中找到UserSession對象，並調用countdown（）方法，並且latch.getCount（）從1變爲0，但latch.await ）方法在UserSession中await（）永遠不會返回。它總是超時。

Answer 1

您可以使用CountDownLatch這樣的：

public class LogonHandler implements Handler { 
    private final CountDownLatch loginLatch = new CountDownLatch (1); 

    private boolean callbackResults; 

    public void serverResponseCallback(boolean result) { 
     callbackResults = result; 
     loginLatch.countDown(); 
    } 

    public boolean tryLogon(Credentials creds) throws InterruptedException { 
     SomeServer server = new SomeServer(address); 
     server.tryLogon (creds.getName(), creds.getPass()); 
     loginLatch.await(); 
     return callbackResults; 
    } 
} 

如果你想限制由等待時間，例如，5秒，然後代替loginLatch.await()使用以下命令：

if (loginLatch.await (5L, TimeUnit.SECONDS)) 
    return callbackResults; 
else 
    return false; // Timeout exceeded