Response Header Lines Controlled by response Object

JSP Tutorials - Herong's Tutorial Examples

∟Response Header Lines Controlled by response Object

This section provides a tutorial example on how to use methods provided by the 'response' object to control HTTP response header line in JSP pages.

The second way and third way to control the response header lines are related to the build-in response object. One is to use specialized methods, the other is to use the generic methods. Let me use the following 2 examples to show you how those methods work.

The first example, SetContentType.jspx, uses the special methods, response.setContentType() and setContentLength(), to set Content_Type and Content_Length header lines:

<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1"> 
<!-- SetContentType.jspx
 - Copyright (c) 2012, HerongYang.com, All Rights Reserved.
-->
 <jsp:scriptlet><![CDATA[
   response.setContentType("text/html");
   String text = "<html><body>Hello world!</body></html>";
   response.setContentLength(text.length());
   out.print(text);
 ]]></jsp:scriptlet>
</jsp:root>

Then view response header lines using my test program, HttpRequestGet.java, presented in the previous section:

C:\>java HttpRequestGet /SetContentType.jspx 8080

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Set-Cookie: JSESSIONID=E13483CEC69A621A3341AB826B4342A2; Path=/; 
   HttpOnly
Content-Type: text/html;charset=UTF-8
Content-Length: 38
Date: 02:37:36 GMT
Connection: close

<html><body>Hello world!</body></html>

The output looks good.

In the second example, SetHeader.jspx, I was trying to use generic methods to set various header lines:

<?xml version="1.0"?>
<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1"> 
<!-- SetHeader.jspx
 - Copyright (c) 2012, HerongYang.com, All Rights Reserved.
-->
 <jsp:scriptlet><![CDATA[
   response.setHeader("Content_Type","text/html");
   response.setIntHeader("Content_Length",0);
   String text = "<html><body>Hello world!</body></html>";
   response.setIntHeader("Content_Length",text.length());
   response.setDateHeader("Last-Modified", 
      System.currentTimeMillis());
   response.setHeader("Author", "Herong Yang");
   response.addHeader("Author", "Joe Wang");
   out.print(text);
 ]]></jsp:scriptlet>
</jsp:root>

Then view response header lines:

C:\>java HttpRequestGet /SetHeader.jspx 8080

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Set-Cookie: JSESSIONID=F536266C7518B697FC940122E8D1A44A; Path=/; 
   HttpOnly
Content_Type: text/html
Content_Length: 38
Last-Modified: 02:47:55 GMT
Author: Herong Yang
Author: Joe Wang
Content-Type: text/xml;charset=UTF-8
Content-Length: 38
Date: 02:47:55 GMT
Connection: close

<html><body>Hello world!</body></html>

Note that:

There are two "Content_Type" header lines, one from my setHeader() call, and one added by Tomcat. My guess is that Tomcat does not recognize the Content_Type header line generated by the addHeader() method. So we have to use setContentType() method to control the Content_Type header line.
The same issue also exists on the "Content_Length" header line. We have to use setContentLength() method to control the Content_Length header line.
The setIntHeader() method is called twice with the same header line name "Content_Length". The second call overrides the first call.
I added two new header lines called "Author".

Here is the revised version of the second example, SetHeaderRevised.jsp:

<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1"> 
<!-- SetHeaderRevised.jspx
 - Copyright (c) 2012, HerongYang.com, All Rights Reserved.
-->
 <jsp:scriptlet><![CDATA[
   response.setContentType("text/html;charset=UTF-8");
   String text = "<html><body>Hello world!</body></html>";
   response.setContentLength(text.length());
   response.setDateHeader("Last-Modified", System.currentTimeMillis());
   response.setHeader("Author", "Herong Yang");
   out.print(text);
 ]]></jsp:scriptlet>
</jsp:root>

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

JavaBean Objects and "useBean" Action Elements