Transcript A communications model

Web Application
Development
Lec 25
Web Application Development
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we used J2SE until now
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For web application development, we need
J2EE (Servlets API, JSP API, JSF API etc)
Web Based Performance Review
Management System
Web Based
School Management System
What is a Web Application
HTTP Communication Model
A communications model
• Client, often but not always a web browser,
sends a request for a resource to a server.
•The server returns a response or an error message.
• Stateless
• No immediate feedback
• No details on how request is made
HTTP Communication Model
Different clients like
•Web browsers
•FTP clients (e.g., interarchy on MacOS X)
•Software registration programs
•telnet
HTTP Communication Model
Web Server?
Software that provides services to access the Internet, or an
intranet.
A web server hosts web sites Provides support for HTTP and
other protocols Executes server-side programs (such as CGI
scripts or servlets) that perform certain functions.
HTTP
HTTP Basics
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HTTP is a request-response oriented protocol.
Parts of an HTTP request
 Request Method
 URI
 Header Fields
 Body
HTTP response contains
 Result Code
 Header Fields
 Body
HTTP Request Example
Request parameters etc
Request Parameters
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Request can also contain additional info in
the form of parameters
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In the URL itself as a query string
http://www.gmail.com/register?name=ali&state=punjab
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As part of the request body
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Shown earlier in the diagram
HTTP Response Example
HTTP Response Codes
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Codes fall into five general categories
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100-199
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200-299
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Values in the 300s are used for files that have moved and
usually include a Location header indicating the new
address.
400-499
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Values in the 200s signify that the request was successful.
300-399
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Codes in the 100s are informational, indicating that the
client should respond with some other action.
Values in the 400s indicate an error by the client.
500-599
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Codes in the 500s signify an error by the server.
Common HTTP Response Codes
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200: means every thing is fine.
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404: Indicates that the requested resource is not
available
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401: Indicates that the request requires HTTP
authentication
403: Indicates that access to the requested
resource has been denied
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503: Indicates that the HTTP server is
temporarily overloaded and unable to handle the
request
Server Side Programming
Static Pages
1 - Request file
2 - Retrieve file
3 - Send file
Example: Static Page
Dynamic Pages
1 - Request service
Do Computation
Generate HTML
page with results
of computation
Return dynamically
generated HTML file
Why build Pages Dynamically?
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The Web page is based on data submitted by the user
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The Web page is derived from data that changes frequently
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E.g. results page from search engines and order
confirmation pages at on line stores
E.g. a weather report or news headlines page
The Web page uses information from databases or other serverside resources
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E.g. an e-commerce site could use a servlet to build a
Web page that lists the current price and availability of
each item that is for sale\
Course Registration System
Course Registration System
What is Server-Side Programming (SSP)?
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Technologies for developing web pages that include
dynamic content.
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Can produce web pages that contain information
that is connection- or time-dependent.
Dynamic Web Content
Technologies Evolution (only figure)
CGI
CGI
(in C)
(java, C++)
Speed, Security
Servlet
(Java)
Template
(ASP,
PHP,CFML)
complexity
JSP
Web-Based Enterprise
Applications in Java
Figure shows a simplified view of one application and its layers.
Java Web Application Technologies
(Presentation/Web Tier)