Http servlet不返回任何值

-3

当我使用Scheduler时，HttpServletResponse没有返回任何值。在下面的代码中直到“RETURNED”在控制台中打印。但是out.println（previousLastLine）的下一行没有返回。任何建议将不胜感激。提前致谢。Http servlet不返回任何值

import java.io.BufferedReader; 
import java.io.FileReader; 
import java.io.IOException; 
import java.io.PrintWriter; 

import javax.servlet.ServletException; 
import javax.servlet.annotation.WebServlet; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 

@WebServlet(value="/notifyController") 
public class NotificationController extends HttpServlet{ 

    int rep = 0; 
    String previousTime = null; 
    String previousLastLine = null; 
    String lastText = null; 
    int count = 0; 
    boolean changeFlag = false; 
    final long timeInterval = 1000; 
    HttpServletResponse response = null; 

    @Override 
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
     response = resp; 
     if(rep == 0){ 
      Runnable runnable = new Runnable() { 
       public void run() { 
        while (true) { 
         changeFlag = scheduleTask(); 
         if(changeFlag == true){ 
          try { 
           System.out.println("RETURNED"); 
           response.setContentType("text/html"); 
           PrintWriter out = response.getWriter(); 
           out.println(previousLastLine); 
           out.flush(); 
          } catch (IOException e) { 
           e.printStackTrace(); 
          } 
         } 
         try { 
          Thread.sleep(timeInterval); 
         } catch (InterruptedException e) { 
          e.printStackTrace(); 
         } 
        } 
       } 
      }; 
      Thread thread = new Thread(runnable); 
      thread.start(); 
      rep++; 
     } 
    } 

    public boolean scheduleTask(){ 
     BufferedReader br = null; 
     try { 
      String sCurrentLine; 
      br = new BufferedReader(new FileReader("D:/messagedetails.txt")); 
      while ((sCurrentLine = br.readLine()) != null) { 
       if(lastText != sCurrentLine){ 
        lastText = sCurrentLine; 
       } 
      } 
      if(count == 1 && !previousLastLine.equalsIgnoreCase(lastText)){ 
       previousLastLine = lastText; 
       return true; 
      } 
      previousLastLine = lastText; 
      count = 1; 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } finally { 

      try { 
       if (br != null)br.close(); 
      } catch (IOException ex) { 
       ex.printStackTrace(); 
      } 
     }  
     return false; 
    } 
}

来源

2016-04-15 Prasanna Venkat

有没有在日志中的异常？ – brso05

你想实现长轮询吗？如果是这样，你在@WebServlet注释中缺少asyn属性。检查这个http://stackoverflow.com/questions/8081895/implementing-long-polling-in-an-asynchronous-fashion – Walfrat