Java Servlet和SSE中的連接關閉

Question

我嘗試在服務器上使用Java Serlvet在Webapp中實現Server-Sent-Event。

是否可以在Servlet中檢查連接是否被客戶端關閉？即使客戶端瀏覽器關閉，Servlet中的循環while(true)也是無限的。

客戶端代碼

function startLogSSE(lastEventId, level) { 
     var eventSource = new EventSource("log-sse?last-event-id=" + lastEventId + "&level=" + level); 
     eventSource.onmessage = function (event) { 
      document.getElementById('log').innerHTML = event.data + "\n" + document.getElementById('log').innerHTML; 
     }; 
    } 

Server代碼

public class LogSSEServlet extends HttpServlet { 
    private static final Logger logger = LoggerFactory.getLogger(LogSSEServlet.class); 

    @Override 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
     response.setContentType("text/event-stream"); 
     response.setCharacterEncoding("UTF-8"); 

     PrintWriter writer = response.getWriter(); 

     // get logger purgerDB appender 
     PurgerDBAppender appender = LogUtils.getPurgerDBAppender(); 
     if (appender == null) { 
      writer.write("data: [ERROR] Appender 'purgerDB' isn't found for logger 'com.bp3'\n\n"); 
      writer.close(); 
      return; 
     } 

     int eventId = 0; 
     // get last-event-id 
     String lastEventId = request.getHeader("last-event-id"); 
     if (lastEventId == null) { 
      // try to get lastEventId from parameter 
      lastEventId = request.getParameter("last-event-id"); 
     } 
     if (lastEventId != null) { 
      try { 
       eventId = Integer.parseInt(lastEventId); 
      } catch (NumberFormatException e) { 
       logger.error("Failed to parse last-event-id: " + lastEventId); 
      } 
     } 
     String minLevel = request.getParameter("level"); 
     if (minLevel == null) { 
      minLevel = "TRACE"; 
     } 

     // get logs from purgerDB logger appender 
     LogServices logServices = new LogServices(); 
     try { 
      logServices.open(); 
     } catch (SQLException e) { 
      throw new ServletException(e); 
     } 
     try { 
      while (true) { 
       List<LogMessage> messages = logServices.getLastMessages(Level.toLevel(minLevel), eventId, 0); 
       if (messages.size() > 0) { 
        writer.write("id: " + messages.get(0).getEventId() + "\n"); 
        writer.write("data: " + LogUtils.formatLog(messages) + "\n"); 
        writer.flush(); 
       } 
       try { 
        Thread.sleep(100); 
       } catch (InterruptedException e) { 
        break; 
       } 
      } 
     } catch (SQLException e) { 
      throw new ServletException(e); 
     } finally { 
      logServices.closeQuietly(); 
     } 
    } 
} 

Answer 1

是否有可能在Servlet來檢查連接是由客戶端關閉？

最後一個將引發異常：要麼一個IOException: connection reset如果直接流傳輸到所述插座，或OutOfMemoryError如果容器流至存儲器，其中，當不使用固定長度或不分塊傳輸模式。

即使客戶端瀏覽器關閉，Servlet中while（true）的循環也是無限的。

不，它不是。

Answer 2

使用writer.checkError()方法檢查連接是否已關閉的一種方法是驗證Servlet。我在Chrome上測試了這個修補程序，它可以正常工作您的代碼將是：

  boolean error=false; 
      while (!error) { 
       //...     
       writer.write("data: " + /*...*/ "\n"); 
       //writer.flush(); 
       error = writer.checkError(); //internally calls writer.flush() 
      } 

詳細：

的PrintWriter's API說：

方法在這個類不會拋出I/O異常，儘管它的一些 構造的可能。客戶可以通過調用checkError()來詢問是否發生了錯誤 。

和checkError()說：

刷新流，如果沒有關閉，並檢查其錯誤狀態