【大学课件】基于Web的应用系统开发

A widely used form of communication
Server application waits passively for contact from clients
A server provides a specific service
Client application actively initiates contact with the server
7
.
General Server Characteristics
Web servers have two main directories:
• 1. Server root (server system software) • 2. Document root (servable documents)
ported to other platforms by late 1993
Current common browsers
• Internet Explorer, Netscape, Opera, Mozilla Firefox, Safari, Google Chrome (as of 9/3/08)
• Monitor a communications port on the host, accepting HTTP messages when they appear
Common servers
• Apache, Internet Information Server (IS)
5
.
Uniform Resource Locators (URLs)
基于Web的应用系统开发
4. Web browsers, servers and HTTP
1
.
Overview
Client-server paradigm Web browsers Web servers URL MIME HTTP
2
.
The client server paradigm
Allow user to browse resources available on server
• either existing or dynamically built documents
Mosaic - NCSA (Univ. of Illinois), in early 1993
• First to use a GUI, led to explosion of Web use • Initially for X-Windows, under UNIX, but was
• This will map to the URL of the full domain name, e.g.:
http://www.hit.edu.cn/
• User document root directory
• Directories of a standard name in the users home directory
Second part - varies according to protocol
• mailto - e-mail address e.g.:
• mailto: wjsun@hit.edu.cn
• resource-oriented protocols (http, ftp etc)
• Host name + domain names (preceded by //)
Optional third parts
• Query string (preceded by ?)
• Fragment identifier (preceded by #)
6
.
Example URLs
mailto:wjsun@hit.edu.cn http://www.hit.edu.cn/ http:// www.hit.edu.cn :80/ http://tpm.hit.edu.cn:8799/ http://uname:pword@tpm.hit.edu.cn/private/secret.html http://tpm.hit.edu.cn/dbase?stuff http://tpm.hit.edu.cn/myfile.html#third ftp://uname:pword@tpm.hit.edu.cn/ ftp://tpm.hit.edu.cn/
Standard way of specifying entities on networks
First part - protocol
• terminated by colon ( : )
• common protocols are http, ftp, mailto, telnet,
• i.e.: http: ftp: mailto: telnet:
Information can flow in both directions
Typical situation is many clients interacting with each server
3
.
Web Browsers
Browsers are clients
• always initiate, servers react
• may optionally include username, password and port
• Pathname (usually related to the path of a file on the server)
• i.e. //fully-qualified-domain-name/path-to-document
Байду номын сангаас
4
.
Web Servers
Provide responses to browser requests
All communications between browsers and servers use Hypertext Transfer Protocol (HTTP)
Web servers run as background processes in the operating system