How CGI and Java Servlets are Run By David Stein 14 November 2006

CGI

What is CGI? Common Gateway Interface server side program or script used to process data entered into an online form commonly referred to as a script

What is needed in order to create and run a CGI program? Computer with: 1. Internet access 2. Web browser 3. Text editor Access to a web server Knowledge of HTML and a programming/scripting language

What languages are associated with CGI Any programming language that can be run or executed in a server environment – C – C++ – Visual Basic – PHP – Perl – Java – Etc…

How is a CGI program run? 1. User requests a web page 2. Web server responds with request 3. User enters data into an HTML form and sends it back to the web server HTML form (Get or Post) 4. Server receives the request from the user and processes the form Compiled or Interpreted 5. Server responds with appropriate data to the user

CGI Process Internet HTTP Request HTTP Response Script Processed

Example Form HTTP request for a webpage HTTP Request – Request Line Command, URL ( _form.html), and HTTP version – Request Header Variety of optional info (i.e. web browser and date) – Request Body Information that needs to be sent to the server – Data typed into the form

HTTP Response Response Status – HTTP version #, server, status code (200 or 400), and a response phrase Response Header – Variety of optional info (web server used, date, exact URL of page, etc….) Response Body – Webpage

Processed PHP Script Your Feedback <?php // handle_php.php //This page receives the data from feedback.html. //It will receive: title, name, , response, comments, and submit print "Thank you $title $name for your comments. "; print "You stated that you found this example to be $response and added: $comments"; ?>

Java Servlets

What are Java Servlets? Modules of Java code that run in a server application (similar to an applet on the client side) Counterpart to dynamic web technologies such as PHP, ASP.Net, etc…

Uses of Java Servlets Processing/storage of data submitted by an HTML form Provide dynamic content to a web server Managing of state information on top of stateless HTTP

Java Servlet Process Internet HTTP Request HTTP Response Developer with JSDK Java VM (servlet engine) Client

Example Java Servlet Code import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloClientServlet extends HttpServlet { protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); PrintWriter out = res.getWriter(); out.println(" Hello Client! "+ " Hello Client! "); out.close(); } public String getServletInfo() { return "HelloClientServlet 1.0 by Stefan Zeiger"; }

Servlet Output

Servlet Advantages Over CGI Servlet does not run in a separate process – (removes overhead of creating a new process) Servlet stays in memory between requests Servlet can be run in restrictive Sandbox

Sources PHP (Visual Quick Start Guide) – By Larry Ullman essentials essentials fcs/doc/Servlets.html fcs/doc/Servlets.html er.html er.html