Introduction To Web Application

Alex

Topic

No programming detail Not for some specific programming

language Focus on what it is Focus on how it works

Outline

Client Server Communication HTTP Static Web Web Server Client Side Script Dynamic Web Application Server Beyond This

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

HTTP

Application Layer Protocol URL As Address Address Stack

– HTTP: URL (domain + path)

– TCP: ip + port

– IP: ip

– 802.11x: mac address

– Hardware: broadcast

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

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

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

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

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

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?

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

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

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

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

Application Server

PHP

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

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

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)

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)

Beyond This

Web Service Web Socket High Performance Web High Availability Distribute Web

Q & AThank!