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 it's 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_HOMEIn 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'?>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.
<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>
index.jsp
<html>This is the index.jsp page. Here we have four links to four different cgi scripts.
<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>
$ ls *This is how the directory structure looks like. Note the cgi-bin directory.
index.html
cgi-bin:
script.pl script.py script.rb script.sh
META-INF:
resin-war.digest
WEB-INF:
classes tmp web.xml
Scripts
Next we will show all four CGI scripts. They all print environment variables.script.sh
#!/bin/shThis is the shell CGI script.
echo "Content-Type: text/html"
echo
echo "<pre>"
env
echo "</pre>"
script.py
#!/usr/bin/pythonThis is the Python CGI script.
import sys
import os
from cgi import escape
print "Content-type: text/html"
print "<pre>"
for k in sorted(os.environ):
print "<b>%s: </b>%s" %(escape(k), escape(os.environ[k]))
print "</pre>"
script.rb
#!/usr/bin/rubyThis is the Ruby CGI script.
puts "Content-Type: text/html"
puts
puts "<pre>"
ENV.to_hash.each do |key, value|
puts("<b>#{key}</b>: #{value}")
end
puts "</pre>"
script.pl
#!/usr/bin/perlFinally, this is the Perl CGI script.
print "Content-type: text/html\n\n";
print "<pre>";
foreach $key (sort keys(%ENV)) {
print "<b>$key</b>: $ENV{$key}";
print "<br>";
}
print "</pre>";
Figure: CGI script
In this chapter, we have used the Resin's CGIServlet to launch Python, PERL and Bash scripts. 
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