Saturday, January 21, 2017

JSP - Auto Refresh

Consider a webpage which is displaying live game score or stock market status or currency exchange ration. For all such type of pages, you would need to refresh your web page regularly using refresh or reload button with your browser.

JSP makes this job easy by providing you a mechanism where you can make a webpage in such a way that it would refresh automatically after a given interval.
The simplest way of refreshing a web page is using method setIntHeader() of response object. Following is the signature of this method:
public void setIntHeader(String header, int headerValue)
This method sends back header "Refresh" to the browser along with an integer value which indicates time interval in seconds.

Auto Page Refresh Example:

Following example would use setIntHeader() method to set Refresh header to simulate a digital clock:
<%@ page import="java.io.*,java.util.*" %>
<html>
<head>
<title>Auto Refresh Header Example</title>
</head>
<body>
<center>
<h2>Auto Refresh Header Example</h2>
<%
   // Set refresh, autoload time as 5 seconds
   response.setIntHeader("Refresh", 5);
   // 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;
   out.println("Crrent Time: " + CT + "\n");
%>
</center>
</body>
</html>
Now put the above code in main.jsp and try to access it. This would display current system time after every 5 seconds as follows. Just run the JSP and wait to see the result:



Auto Refresh Header Example

Current Time is: 9:44:50 PM
To become more comfortable with other methods you can try few more above listed methods in the same fashion.
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