indroduction to web application from history to principle forcus on what it is and how it works

1. Introduction To Web Application
Alex

2. Topic

No programming detail

Not for some specific programming
language

Focus on what it is

Focus on how it works

3. Outline

Client Server Communication

HTTP

Static Web

Web Server

Client Side Script

Dynamic Web

Application Server

Beyond This

4. Client Server Communication

Server listen

Client send a request

Server send a response back

OSI Stack
– Application Layer
– Transport Layer
– Network Layer
– Data Link Layer
– Physical Layer

5. HTTP

Application Layer Protocol

URL As Address

Address Stack
– HTTP: URL (domain + path)
– TCP: ip + port
– IP: ip
– 802.11x: mac address
– Hardware: broadcast

6. HTTP

HTTP Request
– Header (Key-Value Text)
• Address (Host, Get or Post)
• Describe Body
• Describe Client
• Other Stuff
– Body
• Post Parameters (key=value)
• Files
• Carry whatever you want

7. HTTP

HTTP Response
– Header (Text Key Value Pairs)
• Response Status (2xx 3xx 4xx 5xx)
• Describe Body
• Other Stuff
– Body
• Browser case : HTML js css
• Download case : anything you downloaded

8. Static Web

Document Sharing

Connection between Documents – Hyper
Link

Document is text and more than text

Hyper Text = text + hyper link

HTML = Hyper Text + style

Hyper Text Markup Language

9. Web Server

Manage static document files

Give client what it ask for

Apache Lighttpd Nginx etc

How it works
– Listen on a port (default 80)
– Accept a http request
– Locate the document client wants
– Send that back to client as a http response

10. Client Side Script

More than display and link
– Animation
– Response user action immediately
– Some logic can run on client

Browser can run
– Javascript
– Flash
– Sliver light
– VB Script, Java Applet, ActiveX, Extensions

11. Dynamic Web

Think about a forum
– User generate content
– Topics changes all the time

You can not do this static way
– We need more then static files
– We need to run a program when we accept
a http request to generate response

How?

12. Dynamic Web

New Way
– Listen to a port (default 80)
– Accept a http request
– Processing request
• If static content, return that stupid file
• If dynamic run a program return that result
– Send result back as a http response

13. Application Server

More then web server
– An URL can map to a static file
– An URL can map to a processing logic

Ancient Way
– CGI just run a executable program and
return the standard output
– Fast CGI : thread based

14. Application Server

Now it works, functionally

People finally got Web Application

But it sucks
– If we write an address which we should not
write, Crash!
– Print each line of html
– Heavy work just for a forum

15. Application Server

Most Web Applications do not need
memory manipulate

Output html in html way

Solution
– Interpret server side script in a html
template when processing a request
– Php is short for Php Home Page
– Asp jsp rhtml

16. Application Server

PHP

17. Application Server

How it works
– Listen to a port (default 80)
– Accept a http request
– Processing request
• If static content, return that stupid file
• If dynamic
– Run the interpreter such as php interpreter
– The interpreter interpret user program(php file)
– Interpreter return the interpret result
– Send result back as a http response

18. Application Server

PHP style language limitation
– Each interpreter instance for a request
– No server global context
– Low performance nature

JAVA style (JAVA .NET)
– Virtual machine execution (keep
programmer from low level memory ops)
– Compile instead interpret (greatly improve
performance)
– Web app and server all run in One VM

19. Application Server

How it works (JAVA style)
– JVM start a JAVA program (that's server)
– Listen to a port (default 80)(run in VM)
– Accept a http request (run in VM)
– Processing request (run in VM)
• If static content, return that stupid file
• If dynamic
– Parse the http request
– Call the user define method which should
process this request,
– Send result back as a http response(run in
VM)

20. Application Server

JAVA program server should be
– Tomcat (widely used)
– Jetty (we use in current project)
– Websphere (widely used in commercial)

The user define method should be
– doGet(request, response)
– doPost(request, response)

21. Beyond This

Web Service

Web Socket

High Performance Web

High Availability

Distribute Web

22. Q&A
Thank!