Lecture 6: Web Servers+Intro to JSP

1

Web Servers



•
How do our requests
for resources on the
Internet get handled?

•
Can they be located
anywhere? Global?

2

Web Servers

•
Looking at ….

–
Introduction to web servers

–
HTTP request types

–
3
-
tier system architecture

–
Accessing a web server (local and remote)

–
Web server examples

•
Apache

•
Tomcat

•
IIS

•
PWS

3

What is a web server?

•
Web server

–
Specialized software that responds to client
requests by providing resources (web pages,
documents, etc..)

–
Based on the client/server model

–
When users enter URL into Web browsers, they
request specific documents from Web server

–
Maps URL to file on server and returns requested
document to client

–
Communicates with client using HTTP

•
Protocol for transferring requests and files over the
Internet

4

HTTP Request Types

•
Also known as request methods

•
Most popular are
get

and
post

–
Retrieve and send client form data to Web server

–
get

request

•
Sends form content as part of URL

•
Retrieves appropriate resource from Web server

•
Limits query to 1024 characters

–
post

request

•
Updates contents of Web server (posting new messages to
forum)

•
Has no limit for length of query

•
Not part of URL and cannot be seen by user

5

HTTP Request Types

•
get

and
post

requests are sent to a server
-
side form handler

•
Client browsers cache (save on disk) Web
pages

–
Allows for quick reloading

–
Cache responses to
get

request

–
Do not cache responses to
post

request

6

System Architecture

•
A web server forms part of a multi
-
tier
application

–
Divide functionality into separate tiers

•
Logical groupings of functionality

•
Can reside on same computer or on different
computers

•
What does a 3
-
tier architecture look like?

–
let’s have a look

7

System Architecture

App lica tion
Mid dle t ier
Inf ormat ion t ie r
Client t ie r
Da ta ba se
8

System Architecture

•
Client tier

–
Referred to as the top tier

–
Application’s user interface

–
Users interact with application through user
interface

–
Interacts with middle tier to make requests and
to retrieve data from information tier

–
Displays data to user

9

System Architecture

•
Information tier

–
Referred to as data tier or bottom tier

–
Maintains data for application

–
Stores data in relational database management
system

•
Middle tier

–
Implements business logic and presentation logic

–
Controls interactions between application clients
and application data

–
Acts as intermediary between data in information
tier and application clients

10

System Architecture

•
Middle tier, cont.

–
Controller logic

•
Processes client requests from top tier

•
Retrieves data from database

–
Presentation logic

•
Processes data from information tier

•
Presents content to client

–
Business logic

•
Enforces business rules

–
Dictates how clients can access application data and how
applications process data

•
Ensures data validity before updating database

11

Accessing Web Server

•
Requesting documents

–
Must know machine name on which Web server
resides

–
Through local Web servers or remote Web servers

–
Through domain name or Internet Protocol (IP)
address

•
Local Web server

–
Resides on users’ machines

–
Requests documents in two ways

•
Machine name

•
localhost

–
Host name that references local machine

12

Accessing Web Server

•
Remote Web server

–
Resides on different machines

–
Accessing resources on remote web server
requires

•
Domain name

–
Represents group of hosts on Internet

–
Combines with how name (
www
) and top
-
level domain to from
fully qualified host name

•
Fully qualified host name

–
Provides user friendly way to identify site on Internet

•
IP address

–
Unique address for locating computers on Internet

•
DNS (see notes)

13

Examples of Web Servers

•
Apache (Apache group)

•
Tomcat (Apache group)

•
IIS (Microsoft Internet Information
Services)

•
PWS (Microsoft Personal Web Server)

14

Apache web server

•
Apache

–
Maintained by Apache Software Foundation

–
Currently most popular Web server

•
Stable

•
Efficient

•
Portable

•
(got it’s name from the original developers
who called it ‘
a patchy

server’)

15

Apache web server

•
Open source

–
Freely distributed on the Internet

–
Huge amount of end
-
user support

–
Has earned the reputation of being one of the
most reliable web server available

•
Uses server modules to add functionality to
the core HTTP server

–
i.e. extra services that it can provide (e.g.
security authentication)

16

Apache web server

•
To launch Apache, successively select

–
Start, Programs, Apache httpd Server, Control
Apache Server

and
Start

17

Tomcat web server

•
Tomcat

–
Similar to Apache and also maintained by
Apache Software Foundation

–
Fast becoming a popular Web server

–
Built in Servlet container (engine)

–
Requires no add
-
ons to support Servlets

18

Tomcat web server

•
To launch Tomcat, successively select

–
Start, Programs, Apache Tomcat 4.x
and
Start
Tomcat

19

Internet Information Services
(IIS) web server

•
Developed by Microsoft

•
IIS 5.0

–
Enterprise
-
level Web server

–
Included with Windows 2000

–
Allows computer to serve documents

•
Uses an Internet Services Manager to
administrate

–
see diagram

20

Internet Information Services
(IIS) web server

Internet Services Manager

dialog.

21

Personal Web Server (PWS)

•
PWS developed by Microsoft

•
PWS

–
Scaled
-
down version of IIS

–
Intended for personal computers (PC)

–
Ideal for educational institutions, small
businesses and individuals

–
Does not require PC to be used exclusively as
Web server

–
A Personal Web Manager is used to
administrate it

22

Personal Web Server

Personal Web Manager

dialog.

23

References

•
Check out

–
http://www.apache.org

•
Apache and Tomcat documentation

•
Apache and Tomcat are free to download and install

–
http://www.microsoft.com

•
IIS and PWS documentation

24

Summary

•
We have looked at:

–
Introduction to web servers

–
HTTP request types

–
3
-
tier system architecture

–
Accessing a web server (local and remote)

–
Web server examples