Perl

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Contents

CGI

Modules

CGI::Application

  • builds upon CGI adding a structure for writing truly reusable Web-applications
  • "run-mode" - single screen of an application
  • "Mode Parameter" is used to store (and retrieve) the current run-mode of your application
  • maps each run-mode to a specific Perl subroutine ("Run-Mode Method") that implements the behavior of a single run-mode
  • an "abstract class", and is only used via inheritance
package Your::Web::Application;
use base 'CGI::Application';
  • setup() method defines a map between run-modes and run-mode methods
  • run-mode methods are responsible for setting up the HTTP and HTML output
  • run-mode methods should never print() anything to STDOUT
  • run() method is singularly responsible for actually sending all HTTP headers and HTML content to the Web browser
  • your run-mode method is called by the run() method, and your code is expected to return a scalar containing all your HTML content
  • header_type() and header_props() allow to change the default HTTP headers
  • "Instance Script" manages a single "instance" of your "Application Module"
  • widgetview.cgi - instance script
#!/usr/bin/perl -w
use WidgetView;
my $app = WidgetView->new();
$app->run();
  • WidgetView.pm - application module, must be in Perl's search path (@INC)
   package WidgetView;
   use base 'CGI::Application';
   use strict;

   # Needed for our database connection
   use DBI;

   sub setup {
	my $self = shift;
	$self->start_mode('mode1');
	$self->run_modes(
		'mode1' => 'showform',
		'mode2' => 'showlist',
		'mode3' => 'showdetail'
	);

	# Connect to DBI database
	$self->param('mydbh' => DBI->connect());
   }

   sub teardown {
	my $self = shift;

	# Disconnect when we're done
	$self->param('mydbh')->disconnect();
   }

   sub showform {
	my $self = shift;

	# Get CGI query object
	my $q = $self->query();

	my $output = '';
	$output .= $q->start_html(-title => 'Widget Search Form');
	$output .= $q->start_form();
	$output .= $q->textfield(-name => 'widgetcode');
	$output .= $q->hidden(-name => 'rm', -value => 'mode2');
	$output .= $q->submit();
	$output .= $q->end_form();
	$output .= $q->end_html();

	return $output;
   }

   sub showlist {
	my $self = shift;

	# Get our database connection
	my $dbh = $self->param('mydbh');

	# Get CGI query object
	my $q = $self->query();
	my $widgetcode = $q->param("widgetcode");

	my $output = '';
	$output .= $q->start_html(-title => 'List of Matching Widgets');

	## Do a bunch of stuff to select "widgets" from a DBI-connected
	## database which match the user-supplied value of "widgetcode"
	## which has been supplied from the previous HTML form via a 
	## CGI.pm query object.
	##
	## Each row will contain a link to a "Widget Detail" which 
	## provides an anchor tag, as follows:
	##
	##   "widgetview.cgi?rm=mode3&widgetid=XXX"
	##
	##  ...Where "XXX" is a unique value referencing the ID of
	## the particular "widget" upon which the user has clicked.

	$output .= $q->end_html();

	return $output;
   }

   sub showdetail {
	my $self = shift;

	# Get our database connection
	my $dbh = $self->param('mydbh');

	# Get CGI query object
	my $q = $self->query();
	my $widgetid = $q->param("widgetid");

	my $output = '';
	$output .= $q->start_html(-title => 'Widget Detail');

	## Do a bunch of things to select all the properties of  
	## the particular "widget" upon which the user has
	## clicked.  The key id value of this widget is provided 
	## via the "widgetid" property, accessed via the CGI.pm
	## query object.

	$output .= $q->end_html();

	return $output;
   }

References

CGI::Builder

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