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(Continued from previous part...)
Controlling Response Header Lines
When a JSP page is requested, the response header lines will be created by the
JSP server. But you can indirectly control some header lines in three 3 different
ways:
1. Using a directive element to set the entity header line: Content_Type, as shown
in the following example:
<jsp:directive.page contentType="text/html"/>
2. Using special methods on the "response" object, as defined by the javax.servlet.ServletResponse interface,
to set the entity header lines: Content_Type and Content_Length as shown in the following example:
response.setContentType("text/html");
responee.setContentLength(909);
3. Using generic methods on the "response" object, as defined by the
javax.servlet.http.HttpServletResponse interface, to add or set any response header lines
as shown in the following example:
response.setHeader("Content_Type", "text/html");
response.setIntHeader("Content_Length", 909);
response.setDateHeader("Last-Modified", System.currentTimeMillis());
response.addHeader("Content_Type", "charset=ISO-8859-1");
Viewing 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 get some limited information
from the 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 wrote the following program to dump the entire
response including all header lines received from a Web server:
/**
* HttpRequestGet.java
* Copyright (c) 2002 by Dr. Herong Yang. 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());
}
}
}
(Continued on next part...)
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