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Asher ImtiazForman Christian College
Umair JavedLUMS
Web Application Development
� We used J2SE until now
� For web application development, we need J2EE (Servlets API, JSP API, JSF API etc)
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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
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Different clients like
•Web browsers
•FTP clients (e.g., interarchy on MacOS X)
•Software registration programs
•telnet
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.
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Web Application Development
� 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
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� Protocol used by ALL Web communications
� HTTP Methods
� GET - Fetch a document
� POST - Execute the document, using the data in
body
� HEAD - Fetch just the header of the document
� PUT - Store a new document on the server
� DELETE - Remove a document from the server
*Taken from Programming the World Wide Web book
Request parameters etc
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� Request can also contain additional info in the form of parameters
� In the URL itself as a query stringhttp://www.gmail.com/register?name=ali&state=punjab
� As part of the request body
▪ Shown earlier in the diagram
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� Codes fall into five general categories
� 100-199
▪ Codes in the 100s are informational, indicating that the client should respond with some other action.
� 200-299
▪ Values in the 200s signify that the request was successful.
� 300-399
▪ Values in the 300s are used for files that have moved and usually include a Location header indicating the new address.
� 400-499
▪ Values in the 400s indicate an error by the client.
� 500-599
▪ Codes in the 500s signify an error by the server.
� 200: means every thing is fine.
� 404: Indicates that the requested resource is not available
� 401: Indicates that the request requires HTTP authentication
� 403: Indicates that access to the requested resource has been denied
� 503: Indicates that the HTTP server is temporarily overloaded and unable to handle the request
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2 - Retrieve file
3 - Send file
1 - Request file
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Do Computation
Generate HTML
page with results
of computation
Return dynamically
generated HTML file
1 - Request service
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� The Web page is based on data submitted by the user
� E.g. results page from search engines and order confirmation pages at on line stores
� The Web page is derived from data that changes frequently
� E.g. a weather report or news headlines page
� The Web page uses information from databases or other server-side resources
� 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
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� Technologies for developing web pages that include dynamic content.
� Can produce web pages that contain information that is connection- or time-dependent.
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CGI(in C)
Template
(ASP,
PHP,CFML)
Servlet(Java)
CGI(java, C++)
JSP
Speed, Securitycomplexity
Figure shows a simplified view of one application and its layers.
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Web Application Development
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http://en.wikipedia.org/wiki/Web_server
� Jakarta is an Apache project� Tomcat is one of its subprojects
� Tomcat is the official reference implementation for the Java servlet and JavaServer pages technologies (according to Sun’s specifications)
� Tomcat is developed in an open and participatory environment and released under the Apache software license
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� Details in Handout
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