Resin CGIServlet

In this tutorial, we will show how to use Resin's CGIServlet.

The CGI (Common Gateway Interface), is a protocol for calling external software via a web server to deliver dynamic content. Resin enables this protocol through its CGIServlet.

CGIServlet

Implements CGI calls. The URL is assumed to refer to an executable file. The operating system is instructed to execute the program or script. The usual CGI environment variables are set, and the current directory is the value of $RESIN_HOME.

In our code example, we will demonstrate how to execute a shell script, Python script, Ruby script and a Perl script.

web.xml
<?xml version = '1.0' encoding = 'UTF-8'?>
<web-app>
  <description>CGI scripts</description>
  <servlet>
    <servlet-name>cgi</servlet-name>
    <servlet-class>com.caucho.servlets.CGIServlet</servlet-class>
  </servlet>
  
  <servlet-mapping>
    <servlet-name>cgi</servlet-name>
    <url-pattern>/cgi-bin/*.sh</url-pattern>
    <url-pattern>/cgi-bin/*.py</url-pattern>
    <url-pattern>/cgi-bin/*.rb</url-pattern>
    <url-pattern>/cgi-bin/*.pl</url-pattern>
  </servlet-mapping>
  
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
  
</web-app>

This is the web.xml file. Here we map all URLs with .sh, .py, .rb and .pl extensions to the CGIServlet. Traditionally, the CGI scripts are placed in a directory called cgi-bin.

index.jsp
<html>
  <head>
    <title>CGI scripts</title>
  </head>
  <body>
   <pre>
   Execute:

   <a href="http://localhost:8080/webapp/cgi-bin/script.sh">shell script</a>
   <a href="http://localhost:8080/webapp/cgi-bin/script.py">Python script</a>
   <a href="http://localhost:8080/webapp/cgi-bin/script.rb">Ruby script</a>
   <a href="http://localhost:8080/webapp/cgi-bin/script.pl">Perl script</a>
   </pre>
  </body>
</html>

This is the index.jsp page. Here we have four links to four different CGI scripts.

$ ls *
index.html

cgi-bin:
script.pl  script.py  script.rb  script.sh

META-INF:
resin-war.digest

WEB-INF:
classes  tmp  web.xml

This is how the directory structure looks like. Note the cgi-bin directory.

Scripts

Next we will show all four CGI scripts. They all print environment variables.

script.sh
#!/bin/sh

echo "Content-Type: text/html"
echo

echo "<pre>"
env
echo "</pre>"

This is the shell CGI script.

script.py
#!/usr/bin/python

import sys
import os
from cgi import escape

print "Content-type: text/html"
print
print "<pre>"
for k in sorted(os.environ):
    print "<b>%s: </b>%s" %(escape(k), escape(os.environ[k]))
print "</pre>"

This is the Python CGI script.

script.rb
#!/usr/bin/ruby

puts "Content-Type: text/html"
puts

puts "<pre>"
ENV.to_hash.each do |key, value|
    puts("<b>#{key}</b>: #{value}")
end
puts "</pre>"

This is the Ruby CGI script.

script.pl
#!/usr/bin/perl

print "Content-type: text/html\n\n";

print "<pre>";
foreach $key (sort keys(%ENV)) {
   print "<b>$key</b>: $ENV{$key}";
   print "<br>";
} 
print "</pre>";

Finally, this is the Perl CGI script.

CGI scripts
Figure: CGI script

In this chapter, we have used the Resin's CGIServlet to launch Python, PERL, and Bash scripts.