Servlet application to auto refresh a page

Q. Write an application to auto refresh a page in servlet.

Answer:

When we need to refresh the web page automatically after some time, then we can use Servlet setIntHeader() method.  This method sends back header "Refresh" to the browser along with an integer value which indicates time interval in seconds. It is used when we displaying live game score, share market status etc.

Below example shows how to use of setIntHeader() method to set Refresh header to simulate a digital clock.

Refresh.java

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;

// Extend HttpServlet class
public class Refresh extends HttpServlet
{
     // Method to handle GET method request.
     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
     {
          // Set refresh, autoload time as 1 seconds
          response.setIntHeader("Refresh", 1);

          // Set response content type
          response.setContentType("text/html");

          // Get current time
          Calendar calendar = new GregorianCalendar();
          String am_pm;
          int hour = calendar.get(Calendar.HOUR);
          int minute = calendar.get(Calendar.MINUTE);
          int second = calendar.get(Calendar.SECOND);
          if(calendar.get(Calendar.AM_PM) == 0)
               am_pm = "AM";
          else
               am_pm = "PM";

          String CT = hour+":"+ minute +":"+ second +" "+ am_pm;
    
          PrintWriter out = response.getWriter();
      
          out.println("<h1 align='center'>Auto Refresh Page</h1><hr>");
          out.println("<h3 align='center'>Current time: "+CT+"</h3>");
     }
     // Method to handle POST method request.
     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
     {
          doGet(request, response);
     }
}


web.xml

<web-app>
     <servlet>
          <servlet-name>Refresh</servlet-name>
          <servlet-class>Refresh</servlet-class>
     </servlet>
     <servlet-mapping>
          <servlet-name>Refresh</servlet-name>
          <url-pattern>/Refresh</url-pattern>
     </servlet-mapping>  
</web-app>


Output:

auto refresh

It refreshes the browser every second and current time will be changed automatically.
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