1. Server-side Technologies
Technologies that exist at the server side
Where the real work occurs

2. Server-side Technologies
Looking at ….
Client-side scripting v Server-side scripting
Factors in selecting a technology
Older and New technologies
CGI, Fast CGI, Mod Perl, Active Server Pages (ASP), Cold Fusion
Overview of Servlets
Introduction to Java Server Pages (JSP)

3. Client-side scripting v Server-side scripting
Validates user input
Accesses the browser
Enhances Web pages with ActiveX® controls, applets, etc.
Manipulates browser documents
Client-side validation
Reduces number of requests that need to be passed to server
Client-side scripting limitations
Browser dependency
Viewable to users through View Source command
JavaScript most popular client-side script

4. Client-side scripting v Server-side scripting
Server-side scripts
Provides programmers greater flexibility
Generates custom responses for clients
Contains greater programmatic capabilities than client-side equivalents
Has access to server-side software that extend server functionality

5. Server-side options Common Gateway Interface (CGI) Fast CGI Mod Perl
Active Server Pages (ASP)
Personal Home Pages (PHP)
Cold Fusion
Java Servlets
Java Server Page (JSP)

6. Common Features
All server-side frameworks share a common set of features
Read data submitted by the user
Generate HTML dynamically based on user input
Determine information about the client browser
Access database systems
Exploit the HTTP protocol

7. Decision Points
When evaluating which server-side technology to use, you need to consider a number of critical factors
Ease of development
How easily can you build new applications
Performance
How fast can the technology respond to queries
Scalability
Can the technology scale to thousands, even millions of users?
Security
Are there any inherent security vulnerabilities?

8. Common Gateway Interface (CGI)
CGI represents one of the earliest, practical methods for generating web content
Primarily written in the Perl programming language
Unfortunately, some CGI programs suffer from scalability and performance problems
Let us see why this happens

9. CGI Architecture Browser initiates request Web server receives request
For each new request, web server spawns a new operating system process to execute the CGI/Perl program
Create new process
Web Server
Perl/CGI
Browser

10. CGI Architecture
For each browser request, the web server must spawn a new operating system process
CGI/Perl 1
Browser 1
Web Server
Browser 2
CGI/Perl 2
Browser N
Create new process
CGI/Perl N

11. CGI Architecture
Spawning a new operating system process for each request takes time and memory
Hence, CGI programs have inherent scalability and performance problems
Almost all other server architectures address these problems

12. Fast CGI
Developed by Open Market as an option for developing faster, more scalable CGI programs
Works by creating a pool of processes for handling CGI requests
When a server receives a CGI request, Fast CGI picks up one of the processes from the pool and assigns it to the task
Without the overhead of creating new processes each time, Fast CGI is much quicker than traditional CGI

13. Mod Perl A module of the Apache Web server
Embeds the Perl interpreter directly within the web server
Perl programs are therefore precompiled
Since Perl is embedded within the server, Mod Perl does not need to create a new process for each request
Like Fast CGI, Mod Perl is much faster than traditional CGI

14. Server Extensions
Several web servers provide extension APIs (Application Programming Interfaces)
Netscape provides (NSAPI)
Microsoft provides (ISAPA)
Similar to Mod Perl, these programs run directly within the web server
Hence, Server Extensions are much faster than traditional CGI
Usually written in C/C++, they are not portable across web servers
E.g. if you develop using Netscape NSAPI, you cannot run it on Microsoft ISAPA

15. ASP (Active Server Pages)
Developed by Microsoft
Runs on Microsoft’s web server: IIS (Internet Information Server)
Developers add ASP code directly to their HTML pages
When a client requests a page, the web server takes the HTML page, runs the ASP code within the page, and returns the result in another HTML page
Faster than traditional CGI but only works with Microsoft’s IIS

16. Cold Fusion Developed by Allaire Corporation
Provides excellent database access and tools
Very good technology for Rapid Prototyping and Rapid development

17. PHP (Personal Home Pages)
An open source project developed by volunteers
Provides simple and powerful database access and tools
Good for Rapid Application Development

18. Servlet Java’s answer to the CGI script
Do not confuse a servlet with an applet
Applet: a java program that runs within a browser
Servlet: a java program that runs within a web server
Rapidly becoming most popular technology for developing web based applications

19. Servlet Overview
Servlets are a significant development in client/server computing for the web
Java Servlet API – standard extension to Java
Provides a Java class that can be loaded dynamically to expand the functionality of a Java-enabled server
Does not require Java support on the client side

20. Servlet Overview
Provides a generic mechanism for extending the functionality of any kind of server (not just web servers)
e.g. could be used to extend the functionality of a Java-based ftp server, or a mail server to scan for viruses attached to
Makes it easier for applets to communicate with the server
Created to solve one basic need recognised: Generating dynamic web content

21. History of Servlets
In late 1996, the use of Java on the server side was developing
Allows getting away from the use of sockets on the server side
Software vendors were each developing their own approach
Problem: each technology was tied to a particular vendor server program

22. History of Servlets
Better to have a generic technology so that server programs could have the “write-once, run-anywhere” approach
Early 1997, JavaSoft (Sun Microsystems) released the Servlet API
Designed to work on Java and non-Java based servers
Most web servers support Servlets

23. General mechanism Execute within the server’s process space
Each servlet handled by a separate thread within the server process, not as separate processes (as in CGI).
Servlets are portable across different web servers and different operating systems
Fast, powerful and portable replacements to CGI scripts

24. General mechanism
Persist between invocations (CGI scripts reloaded), resulting in significant performance benefits over CGI programs
Servlets have full access to the Java APIs and also to third party component classes (e.g. database connections, etc.)

25. Places where Servlets can be used
Accessed by name to generate a HTML page
Embedded inside a HTML page as a server side include
These are useful when a web page is mostly static info but contains small sections of dynamically-generated info
Embedded inside a HTML page using Java Server Pages (JSP) – see these later

26. 3 types of servlet engine
Standalone
Server that contains built in support for Servlets (e.g. Tomcat)
Does not exist for many web servers
Disadvantage: have to wait for a new server release to get latest servlet support
Add-on
A plug-in for an existing web server
Many have been written for servers (e.g. Apache)
Embedded
Lightweight servlet platform that can be embedded in another application

27. Advantages of Servlets
Servlets have 6 main advantages
Efficient
Convenient
Powerful
Portable
Secure
Inexpensive
Let us see why

28. Advantages of Servlets
Efficient
For each browser request, the servlet spawns a light weight thread
This is faster and more efficient than spawning a new operating system process
Hence, servlets have better performance and scalability than traditional CGI

29. Advantages of Servlets
Convenient
Servlets include built-in functionality for:
Reading HTML from data
Handling cookies
Tracking user sessions
Setting HTTP headers
Java is an object-oriented language which arguably can make development easier

30. Advantages of Servlets
Powerful
Servlets can talk directly to web servers
Multiple servlets can share data
Particularly important for maintaining database connections
Includes powerful techniques for tracking user sessions

31. Advantages of Servlets
Portable
One of the advantages of Java is its portability across different operating systems
Servlets have the same advantages (they are written in Java)
Can be written on a Windows platform and run on a UNIX operating system
Servlets can be run on any Java-enabled web server with no code changes

32. Advantages of Servlets
Secure
Traditional CGI programs have a number of known security vulnerabilities
Hence, a separate CGI/Perl script is usually required to provide the extra security required
Java itself has a number of built-in security features
Therefore, Servlets are regarded to be more secure than CGI programs

33. Advantages of Servlets
Inexpensive
You can download free servlet kits for development
As many servlets that are required can be developed for free and run on many free Java-enabled web servers

34. Servlets Example import javax.servlet.*; import javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws
IOException, ServletException
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<body>");
out.println("<head>");
out.println("<title>Hello World!</title>");
out.println("</head>");
out.println("<h1>Hello World!</h1>");
out.println("</body>");
out.println("</html>"); }

35. Server Pages Microsoft IIS + ASP (Active Server Pages)
Sun followed suit + JSP (JavaServer Pages)

36. Java Server Pages Related to Java servlets
An extension of the Java servlet API
Can be used alone or in conjunction with servlets
Another method for developing server side applications
We will look at these in more detail in next lecture

37. References Check out Fast CGI Mod Perl Active Server Pages (ASP)
Mod Perl
Active Server Pages (ASP)
Cold Fusion
PHP
Servlet and Java Server Page (JSP)

38. Summary We have looked at:
Client-side scripting v Server-side scripting
Factors in selecting a technology
Older and New technologies
CGI, Fast CGI, Mod Perl, Active Server Pages (ASP), Cold Fusion
Overview of Servlets
Introduction to Java Server Pages (JSP)