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IS-907 Java EE World Wide Web - Overview
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IS-907 Java EEWorld Wide Web - Overview
World Wide Web - History
• Tim Berners-Lee, CERN, 1990
• Enable researchers to share information:• Remote Access• Not restricted to particular type of computer(s)• Non-centralised• Access to existing data• Users can add data• Annotations• Data analysis
Web, Internet, internet...
• internet – connection between local networks
• Internet – the global tcp/ip based internet
• (World Wide) Web/W3 – an http-based application that uses the Internet for data transport
Web Architecture
• The World Wide Web uses a client-server architecture
• Clients (browsers) provides the user interface and displays data
• Servers provide data to the clients on request
• Clients and servers are programs
• The client and server can run on the same computer,or on different computers
• The computer where the server runs is often called host
Building blocks of the web
• http – the HyperText Transfer Protocol: The rules for communication between clients and servers.
• URI/URN/URL – Uniform Resource Identifier/ Name/ Locator: The rules for naming data objects on the web.
• html – HyperText Markup Language: The syntax rules for documents.
HyperText Markup Language
• the document format of the web
• standardized:
• http://www.w3.org/standards/techs/html#w3c_all
• XHTML 1.1
• XHTML 1.0 http://www.w3.org/TR/2002/REC-xhtml1-20020801/
• HTML 4.01 http://www.w3.org/TR/html401/
• XHTML is defined as an XML application
• syntax is stricter than plain HTML
• We will use XHTML 1.0
Even Åby Larsen ([email protected]) IS-102 Introduksjon 6
XHTML pages
• starts with a document declaration:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
• The document contains elements (tags)
• the top level element is html
• all tags must have a matching end tag
<h1>Hello World!</h1>
• the end tag can be abbreviated for empty elements:
<br/>
Even Åby Larsen ([email protected]) IS-102 Introduksjon 7
Simple XHTML page
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<meta http-equiv="Content-Type“
content="text/html; charset=UTF-8" />
<title>Hello</title>
</head>
<body>
<h1>Hello World!</h1>
<p><a href="about.html">About...</a></p>
</body>
</html>
Even Åby Larsen ([email protected]) IS-102 Introduksjon 8
Style sheets
• Used to define the layout and visual properties of html documents
• fonts
• colours
• margins
• ...
• Cascading Style Sheets (css)
• http://www.w3.org/TR/CSS2/
Even Åby Larsen ([email protected]) IS-102 Introduksjon 9
Uniform Resource Locators
• General format: scheme://host/path
• Example: http://java.sun.com/j2se/1.5.0/docs/api/
• scheme = http
• host = java.sun.com
• path = j2se/1.5.0/docs/api
• Relative URL
• path from current page to another one.
• if the page http://mynetshop.com/index.html contains a link to products/computers.html
• it is interpreted by the browser as http://mynetshop.com/products/computers.html
The HyperText Transfer Protocol
• Request / Response protocol
• Message format:
• one or more headers
• blank line
• message body
Client Server
Request
Response
HTTP Request Message types
• GET – used for normal links to get a page, image, ...
• HEAD – just like GET, but no page returned
• POST – used to send data to the server
• PUT – create a new object on the web (seldom used)
• DELETE – remove an object from the web
• TRACE
• OPTIONS
• CONNECT
HTTP GET Request Message Example
GET / j2se/1.5.0/docs/api HTTP/1.1
Host: java.sun.com
HTTP Response Message Example
HTTP/1.1 200 OK
Date: Tue, 28 Aug 2006 07:33:45 GMT
Content-Type: text/html
<html>
html document....
The POST Request
The data from a form are transferred in the request body:
POST /register HTTP/1.1
Host=my.host.com
More=headers
paramname=value
...
Simple web server for static content
while (true) {get next request;read contents of file %DOCROOT%/request.path;create a response message;set response headers;set response.body = file contents;send response;
}
Dynamic web pages
• Dynamic presentation
• uses JavaScript and style sheets
• page remains the same
• user may interact with presentation
• Dynamic content
• server respons with different content depending on input
Dynamic content
• The server doesn’t just map the URL to a filename
• It must
• map the URL to a program,
• run the program,
• and send the output of the program in the body of the response
• the program can do anything:
• get data from a file, or a database
• do some computation
• connect to another system
• ...
Running a program...?• Actually running an external program (CGI)
• the server sends the request to another program
• Server ”plugins” (e.g. servlets)• the server handles the request by calling the plugin code
• Scripts inside the html files (ASP, PHP...)• the server reads a file (just as for static content), but scans the file for
commands, and replaces the commands with the result of executing them
web server for dynamic content
while (true) {get next request;create a response message;if (cgi-url) {
extract program name from request;run the program;set response.body=program output;
}else if (plugin-url) {
call the plugin;set response.body=plugin output;
}else {
read contents of file %ROOT%/request.path;if (file contains script) execute script;set response.body = file contents;
}send response;
}
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