Viewing Response Header Lines

JSP Tutorials - Herong's Tutorial Examples - Version 4.03, by Dr. Herong Yang

JSP Tutorials - Herong's Tutorial Examples

∟Viewing Response Header Lines

This section provides a tutorial Java program, HttpRequestGet.java, to view HTTP response header lines.

When the client program receives the HTTP response, it will look at the header lines first. Based on the information contained in the header lines, the client program will decide what to do with the actual response data in the entity body.

If you use a Web browser as a HTTP client program, it will process the data in the entity body differently depending on mainly the "Content_Type" entity header line: displaying the data as it is, rendering the data as a HTML document and displaying the resulting information, or passing the data to other registered programs to handle it.

Once the Web browser finishes processing the entity body, you can view some limited information from header lines. For example, you can click the right mouse button and select the properties command on Internet Explorer, it will display some general properties about this response in a pop up window. The properties displayed are not always identical to the response header lines. The "Modified" property is probably identical to the "Last_Modified" entity header line. The "Type" property is sometime related to the "Content_Type" entity header line, and sometimes related to server side resource that generated the response. For example, if you use Internet Explorer to request hello.jsp from a JSP Web server, and view the page properties, you will see "JavaServer Page" in the "Type" property. But the "Content_Type" header line received from this JSP page is "text/html".

How to view all the header lines received in the HTTP response? I couldn't find any existing tools to do this. So I wrote the following program to dump the entire response including all header lines received from a Web server:

/**
 * HttpRequestGet.java
 * Copyright (c) 2012, HerongYang.com, All Rights Reserved. 
 */
import java.io.*;
import java.net.*;
public class HttpRequestGet {
   public static void main(String[] args) {
      String path = "/index.html";
      int port = 80;
      String host = "localhost";
      if (args.length > 0) path = args[0];
      if (args.length > 1) port
         = Integer.valueOf(args[1]).intValue();
      if (args.length > 2) host = args[2];
      String result = "";
      try {
         Socket c = new Socket(host,port);
         BufferedWriter w = new BufferedWriter(new OutputStreamWriter(
            c.getOutputStream()));
         BufferedReader r = new BufferedReader(new InputStreamReader(
            c.getInputStream()));
         String m = "GET "+ path + " HTTP/1.0";
         w.write(m,0,m.length());
         w.newLine();
         w.newLine();
         w.flush();
         while ((m=r.readLine())!= null) {
            System.out.println(m);
         }
         w.close();
         r.close();
         c.close();
      } catch (IOException e) {
         System.err.println(e.toString());
      }
   }
}

See next tutorials on how to use this program.

Last update: 2012.

Table of Contents

About This Book

JSP (JavaServer Pages) Overview

Tomcat 7 Installation on Windows Systems

JSP Scripting Elements

Java Servlet Introduction

JSP Implicit Objects

Syntax of JSP Pages and JSP Documents

JSP Application Session

Managing Cookies in JSP Pages