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(Continued from previous part...)
Setting Header Lines Directly 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 the 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.jsp, uses the special methods to set Content_Type and
Content_Length header lines:
<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="1.2">
<!-- SetContentType.jsp
Copyright (c) 2002 by Dr. Herong Yang
-->
<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>
The response:
HTTP/1.1 200 OK
Set-Cookie: JSESSIONID=1771F49508924D74AA8B29BB9AB770C8; Path=/
Content-Type: text/html
Content-Length: 38
Date: Tue, 12 Aug 2003 23:05:34 GMT
Server: Apache Coyote/1.0
Connection: close
<html><body>Hello world!</body></html>
Note that the setContentType() method overrides the Content_Type header line completely,
including the charset portion. Here is another calling example,
response.setContentType("text/html;charset=UTF-8").
In the second example, SetHeader.jsp, I was trying to use the generic methods to
set various header lines:
<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="1.2">
<!-- SetHeader.jsp
Copyright (c) 2002 by Dr. Herong Yang
-->
<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>
Here is the response:
HTTP/1.1 200 OK
Set-Cookie: JSESSIONID=6C081157BFD264C3222FB71728C00B4C; Path=/
Content_Type: text/html
Content_Length: 38
Last-Modified: Sat, 23 Mar 2003 13:46:53 GMT
Author: Herong Yang
Author: Joe Wang
Content-Type: text/xml;charset=UTF-8
Content-Length: 38
Date: Sat, 23 Mar 2003 13:46:53 GMT
Server: Apache Coyote/1.0
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="1.2">
<!-- SetHeaderRevised.jsp
Copyright (c) 2002 by Dr. Herong Yang
-->
<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>
(Continued on next part...)
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