Outdated: Using Perl LWP::Debug Module to Debug

This section provides a tutorial example on how to use Perl LWP::Debug module to help debugging JSP applications at the HTTP request and response level.

Note that LWP::Debug module has been deprecated in Perl. This tutorial example is outdated now.

If you have a problem with your JSP application at the HTTP communication level, one good debugging tool is the Perl LWP module. It can be used as a Web browser to talk to your JSP application, and to log everything at the HTTP communication level.

Here is my sample Perl program, reg_client.pl, designed to work with my previous JSP registration application:

#- reg_client.pl
#- Copyright (c) 2002 by Dr. Herong Yang
  use LWP::Debug qw(+);
  use LWP::UserAgent;
  use HTTP::Cookies;
  ($url) = @ARGV;
  $url =  'http://localhost' unless $url;
  $ua = new LWP::UserAgent;
  $cookie_jar = HTTP::Cookies->new;
  &getForm();
  &submitForm();
  exit;
sub getForm {
  $u =  $url.'/RegForm.jsp';
  my $req = new HTTP::Request GET => $u;
  my $res = $ua->request($req);
  $req = $res->request();
  $cookie_jar->extract_cookies($res);
  &dump($req,$res);
}
sub submitForm {
  $u = $url
     .'/RegForm.jsp?name=Mike&pass=None&color=Blue&submit=Submit';
  my $req = new HTTP::Request GET => $u;
  $cookie_jar->add_cookie_header($req);
  my $res = $ua->request($req);
  $req = $res->request();
  $cookie_jar->extract_cookies($res);
  &dump($req,$res);
}
sub dump {
   local ($req,$res) = @_;
   print "\nREQUEST-HEADERS\n";
   print $req->headers_as_string();
   print "\nREQUEST-CONTENT\n";
   print $req->content;
   if ($res->is_success) {
      print "\nRESPONSE-HEADERS\n";
      print $res->headers_as_string();
      print "\nRESPONSE-CONTENT\n";
      print $res->content;
   } else {
      print "\nRESPONSE-ERROR\n";
      print $res->error_as_HTML();
   }
}

A couple of notes to help you to understand this program:

If you run it with "reg_client.pl http://localhost:8080 > client.out" in a command window, you will get the following in the window:

LWP::UserAgent::new: ()
LWP::UserAgent::request: ()
LWP::UserAgent::simple_request: GET http://localhost:8080/RegForm.jsp
LWP::UserAgent::_need_proxy: Not proxied
LWP::Protocol::http::request: ()
LWP::Protocol::http::request: GET /RegForm.jsp HTTP/1.0
Host: localhost:8080
User-Agent: libwww-perl/5.51

LWP::Protocol::http::request: reading response
LWP::Protocol::http::request: HTTP/1.1 200 OK
Set-Cookie: JSESSIONID=887896C93DFFF372EB38818BF9F68DB2; Path=/
Content-Type: text/html;charset=UTF-8
Content-Length: 393
Date: Sat, 28 Dec 2002 20:37:04 GMT
Server: Apache Coyote/1.0
Connection: close

<html><body><b>Registration Form</b>:<br/><form action=RegForm.jsp met
hod=get>Login Name:<input type=text size=16 name=name><br/>Password:<i
nput type=text size=16 name=pass><br/>Favor Color:<input type=text siz
e=16 name=color><br/><input type=submit name=submit value=Submit></br>
</form>Your session ID is 887896C93DFFF372EB38818BF9F68DB2<br/>Last us
er on the server: Nobody<br/></body></html>
LWP::Protocol::http::request: HTTP/1.1 200 OK
LWP::Protocol::collect: read 393 bytes
LWP::UserAgent::request: Simple response: OK
HTTP::Cookies::extract_cookies: Set cookie JSESSIONID => 887896C93DFFF
372EB38818BF9F68DB2
HTTP::Cookies::add_cookie_header: Checking localhost.local for cookies
HTTP::Cookies::add_cookie_header: - checking cookie path=/
HTTP::Cookies::add_cookie_header:  - checking cookie JSESSIONID=887896
C93DFFF372EB38818BF9F68DB2
HTTP::Cookies::add_cookie_header:    it's a match
HTTP::Cookies::add_cookie_header: Checking .local for cookies
LWP::UserAgent::request: ()
LWP::UserAgent::simple_request: GET http://localhost:8080/RegForm.jsp?
name=Mike&pass=None&color=Blue&submit=Submit
LWP::UserAgent::_need_proxy: Not proxied
LWP::Protocol::http::request: ()
LWP::Protocol::http::request: GET /RegForm.jsp?name=Mike&pass=None&col
or=Blue&submit=Submit HTTP/1.0
Host: localhost:8080
User-Agent: libwww-perl/5.51
Cookie: JSESSIONID=887896C93DFFF372EB38818BF9F68DB2
Cookie2: $Version=1

LWP::Protocol::http::request: reading response
LWP::Protocol::http::request: HTTP/1.1 302 Moved Temporarily
Location: http://localhost:8080/RegDone.jsp?color=Blue
Content-Type: text/html;charset=UTF-8
Content-Length: 0
Date: Sat, 28 Dec 2002 20:37:04 GMT
Server: Apache Coyote/1.0
Connection: close

LWP::Protocol::http::request: HTTP/1.1 302 Moved Temporarily
LWP::UserAgent::request: Simple response: Found
LWP::UserAgent::request: ()
LWP::UserAgent::simple_request: GET http://localhost:8080/RegDone.jsp?
color=Blue
LWP::UserAgent::_need_proxy: Not proxied
LWP::Protocol::http::request: ()
LWP::Protocol::http::request: GET /RegDone.jsp?color=Blue HTTP/1.0
Host: localhost:8080
User-Agent: libwww-perl/5.51
Cookie: JSESSIONID=887896C93DFFF372EB38818BF9F68DB2
Cookie2: $Version=1

LWP::Protocol::http::request: reading response
LWP::Protocol::http::request: HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 221
Date: Sat, 28 Dec 2002 20:37:04 GMT
Server: Apache Coyote/1.0
Connection: close

LWP::Protocol::http::request: HTTP/1.1 200 OK
LWP::Protocol::collect: read 221 bytes
LWP::UserAgent::request: Simple response: OK

We have a lot of information here. Let's analyze it quickly.

Last update: 2006.

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

 Managing HTTP Response Header Lines

 Non-ASCII Characters Support in JSP Pages

 Performance of JSP Pages

 EL (Expression Language)

 Overview of JSTL (JSP Standard Tag Libraries)

 JSTL Core Library

 JSP Custom Tags

 JSP Java Tag Interface

 Custom Tag Attributes

 Multiple Tags Working Together

 File Upload Test Application

Outdated Tutorials

 Outdated: Installing Tomcat 4.1.18

 Outdated: Java Class Converted by Tomcat 4.1.18

 Outdated: Hijacking Servlet Converted from JSP

Outdated: Using Perl LWP::Debug Module to Debug

 Outdated: Installing JSTL 1.0 Apache Implementation

 Outdated: Upgrade JDK 1.3 to JDK 1.4 on Tomcat 4.1

 Outdated: Compilation Errors with JDK 1.4

 Outdated: Using JavaBean without Import Element Error

 Outdated: Installing Tomcat 5.5.7

 References

 PDF Printing Version