Java Omar Rana University of South Asia

Course Overview JAVA  C/C++ and JAVA Comparison  OOP in JAVA  Exception Handling  Streams  Graphics User Interface  Event Handling  Game Programming  Graphics  Database Connectivity  Network Programming

J2EE  HTML / CSS  JavaScript  Servlets  JSP  JSF  JAVA Beans  JSP using XML Tags  MVC Architecture  Programming in Layers  XML technologies

Web Application  Java Categories  J2me  J2sdk  J2EE

J2EE Examples

Web Application Model Request Response

Communication model  Web server cannot distinguish if request is made from same browser or not  Its stateless  http doesn’t store any details how request is made

Different Clients  Web browsers  ftp clients

What is web server?  Webserver hosts website and offers protocol http  It takes request and response  It’s a software to provide services to access internet  Web server executes server side programmes

Example  Facebook login  User request something  Client response something  http protocol is used for communication  Example :  Pdf files, doc files

Http  Its a request – response model or oriented protocol  Http request contains the following:  Request Method  URI  Header Fields  Body

Http Response  Http Response contains:  Result code  Header Fields  Body

Http request Example   In Request following are sent:  GET-POST/  URI = home.html  http protocol  Headers : Host : facebook.com User –Agent : Google Chrome Body : Request parameters

HTTP response Example  Status line : tells if its error or ok response  Response headers : Last modified: some date Date: current date Content type: html/text content length: 50

Dynamic Website  Client Sends a request to server  Server side does some computation and response with html page with result generated of computation  Why dynamic pages and not static?

Dynamic Websites   Results depends on our query   Results depends on user login and database

J2EE APPLICATION STRUCTURE

JAVA web application technologies

Servlets  Its a java class  Servlets extend webserver to extend its capability  It allows us to compute on webserver and gives us a response Request Response

Servlets  Any class in java can be written in servlets  We don’t have to write http protocol mechanism  Rich set of libraries of java available in servlets  E.g.  JDBC  Multithreading  E.t.c

Servlet Advantages  Rich set of libraries  Built in multithreading – treats every request as multithread rather than creating new process  Portable across operating systems  Security – jvm verifier

Software's Required  Eclipse / net Beans  Tomcat Server  J2SE  J2EE

Servlet Hello World  To write Servlet we need to extend from  HttpServlet  Import javax.servlet.*;  Import javax.servlet.http.*;