* Web programming
--What's it got to do with databases?
* Almost always a database at bottom of stack
end user <-> browser <-> internet <-> web server <-> database
* DB used to store two things
1) Transactional data for data-centric apps
--most common is E-commerce (inventory, orders, shipments, etc.)
--but most data live in databases!
2) Actual web content
--So change website by just manipulating DB... no coding!
--ex: have tables PROF, CLASSTAUGHT, PAPERWRITTEN, RESEARCHINTEREST
--Add new data to tables means a new prof appears on home page
* What prog. langguages are used in this stack?
1) HTML at web browser
--to tell browser how to render page
2) JavaScript embedded in HTML
--to interact with user at client side
3) Java/Python/PHP and others at server
--to dynamically generate HTML/JavaScript
4) SQL at server (embedded in Java/Python/PHP)
--to interact with DB
* We will focus on doing this in Java (everyone knows it)
--Will not use JavaScript
* Classic model for Java web development
--MVC design pattern
--"model-view-controller"
--Archaic? Possibly!
* At one end user--at other, web server
--User views HTML, takes some action
* This action is passed over internet to web server
--Causes an event to be processed at the "controller"
* Java class that extends "HttpServlet"
* called a "servlet"
--Servlet takes some action (talks to DB?)
* Writes result into Java object
* This is the "model" in MVC
* Then sends to a "JSP" page
--JSP page encapsulates the "view"
* JSP uses the object passed to generate HTML
* HTML is forwarded over internet to browser
* Specific points to discuss:
1) JSP
2) Java servlet
3) How Java can talk to DB
4) How to store data in a session
* JSP
--Stands for "Java server page"
--Nothing more than HTML (possibly JavaScript) with Java inside
--When served to end-user
--Parts outside <% %> passed verbatim
--Code inside <% %> is run
--See www.jsptut.com
--Ex:
<%
int accum = 1;
for (int i = 1; i < 10; i++) {
accum *= i;
%>
<% =i %> factorial is <% =accum %><\p>
<%
}
%>
--Special objects always available:
request: of type HttpServletRequest
session: of type HttpSession
* Java servlet
--Java class extending HttpServlet
--Has a set of event handlers (doPost, doPut, doGet)
--Event handler takes as input request, response
--Can create response itself, if it wants
--But better is to modify request, dispatch it to correct JSP
--Note: specify what servlet to handle event in HTML widget
ex:
--Note: in Google, specify mapping from servlet name to Java class in web.xml
* Talking to DB in Java
--Done using JDBC
--See example!
--basically
PreparedStatement stmt = c.prepareStatement ("SELECT...");
ResultSet rs = stmt.executeQuery ();
// then go thru rs
--Browse java.sql.Statement!
* Sessions
--HTTP is stateless
--Want to remember stuff? Use a session
--Session mapped to user via a client-side cookie
--"session" is a var of type HttpSession that's always available in JSP
--Can access in servlet via HttpServletRequest.getSession ()
* Final notes
--Wep programming is confusing enough
--Gets really nasty when you have to run web server, database, etc.
--We'll use Google AppEngine framework
--You use their web server
--You use their database