Monday, October 8, 2012
Today I am going to post a program that will be able to show all the headers associated with a servlet request;  Here in the code request object is used to get an enumerations of headers associated with the request of the client. Then with a loop one by one all the headers are extracted and their corresponding values are available using the getHeader(String headername) method. All these headers and their values are sent to the client as a dynamically generated html. Also note that the values will differ according to the browser which has been used to send the request.
Screenshot of output as seen on Chrome in Windows7
Here is the code for you -->

import java.io.PrintWriter;
import java.io.IOException;
import java.util.Enumeration;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.annotation.WebServlet;

@WebServlet("/header.html")
public class HeaderViewer extends HttpServlet{

   public void doGet(HttpServletRequest req,HttpServletResponse res)throws IOException,ServletException{
          Enumeration headers=req.getHeaderNames(); 
/*getting enumerations of all headers */
          PrintWriter out=res.getWriter(); 
//getting writer
          out.write("<html><head><title>HeaderViewer</title></head>");
          out.write("<body><h1><center>Headers associated with your request</center></h1>");
         
          while(headers.hasMoreElements()){
                 String header=(String)headers.nextElement(); 
/*extracting header */
                 out.write("</br><b>"+header+" : </b>"+req.getHeader(header));
/* sending header name and its value to client */
          }
          out.write("</body></html>");
          out.close();
   } 
}

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I am a student of BTech Computer Science Engineering from RCCIIT,Kolkata. I am a crazy lover of Java and wants to settle as a Java developer. I have a seven years Java experience with an application developer experience for 2 years. Recently from March 2012 I am a registered S40 app developer for Nokia and has corrected an app of them. I am currently writing blogs to encourage and grow interest in all those who don't know or learning Java.