1.
Basic components of Java Web Programming
a.
Java Web apps typically made with Servlets and
Java Server Pages
b.
The frameworks like Struts built up on these
fundamental structures like Servlets and Java Server Pages
c.
Java Server page itself a servlet
d.
There are other concepts like Filters and
Listener
e.
Many frameworks today use Filters as their
controllers in their MVC models
2.
What is Web Application
a.
A deployable unit of content (Java App) and
configurations (Like Web.xml)
b.
Requested routed to an application using URL
c.
Web application may contain static content ex..
images, css, html pages
d.
Web application may also dynamically generated
content ex.. Java, JSP, listener and filters
e.
Deployment
i.
Can be deployed as WAR (web archive ) file
ii.
Or simply copying entire folder structure and
files
3.
Servlets
a.
Every servlet implements base interface called
“Servlet”
b.
Servlet has 3 stages in its life cycle
i.
Initialize Servlet
ii.
Service Method (the sole purpose of Servlet)
1.
Servlet Service method take 2 parameters,
servlet request object and servlet response object
2.
Servlet request object contains any data
supplied with servlet request
3.
Servlet response object will have servlet return
data
iii.
Destroy Servlet
c.
Though we can implement Servlet interface
directly, its not recommended. We have helper classes that implemented Servlet
interface..ex… GenericServlet or HttpServlet classes..
i.
GenericServlet is protocol agnostic
ii.
HttpServlet is Http protocol specific
4.
Servlet Mapping
a.
For webserver to see the Servlet and execute it,
we need to add a Servlet Mapping
b.
We can add Servlet mapping using Web.xml or
addition annotation within servlet itself
c.
Annotation example ... “@WebServlet(“/home”)”
d.
Request Routing is handled via Web.xml
configuration.
e.
We can have multiple servlet mappings..
f.
The servlet mapping defines which URLs that will
access servlets.. for example if Servlet is mapped to “/home” this means,
servlet invoked when URL http://server/applicationname/home
is hit... Here the application name is the name of application
g.
http://server/applicationname
is called baseURL.. application name is what deployed in Tomcat or any webserver..
this is what we see in Tomcat webapps instance.. ex..
/webapps/{applicationname}/WEB-INF etc..
5.
Initializing a servlet
a.
We can set initial parameters for servlet as initial
state
b.
In case of Annotation, initialization can be done
using “initParams” collection
c.
Example of annotation with init is..
@WebServlet(urlPatterns={“/home”,”*.do”},
initParams={@WebInitParam(name=”Varname”,value=”server1”)}
)
d.
In case of web.xml
<init-param>
<param-name> Varname</param-name>
<param-name> server1</param-name>
</init-param>
e.
In servlet we can using init() method and getInitParameter(“Varname”)
to get the parameter value
f.
Global servlet parameters can be defined in
web.xml as <context-param>.. these can be retrieved from any servlet
using getServletContext().getInitParameter(“Pname”)
6.
Java Server Pages
a.
JSP pages can be coded with HTML , CSS etc.
<!DOCTYPE > tag define type of JSP code.. <!DOCTYPE html> means it HTML code in jsp file
b.
JSP pages are indeed servlets, jsp file is
converted to java class file during compilation
c.
Use Directive <%@include file=”filanme”>
to include a file with in jsp file
d.
<%= classmethod() %> to execute a class
methods like getName(), setName() etc
7.
MVC
a.
A common idiom in web applications today is
using some thing called Model View Controller
i.
Model – which is data we like to display
ii.
View – which is the place where we display
iii.
Controller – Which is to bring Model and View
together
8.
In MVC
a.
Servlet used as controller (usually!)
b.
JSP used as the view
c.
Beans used as
model (POJO – plain old java object)
d.
Beans could be just as simple as old core java
classes
e.
In servlet, doGet (or in doPost) methods, we can
create an instance of the Bean (an instance of class). We can then pass request
on to JSP page to display this data. To do that, we need to something called requestDispatcher…
requestDispatcher is available through
servlet context… i.e. getServletContext().gerRequestDispatcher()
f.
We passed the control to JSP page via gerRequestDispatcher
object. We also need to tell JSP page how to get the Bean. This can be done
request.setAttribute(“paramvalue”,Paramname)
g.
To hide JSP pages from publicly available, we need
to create JSP pages in WEB-INF folder
9.
Expression Language
a.
Used in JSP pages.. is very easy use.. do not
need Java skills
b.
Allows more dynamic pages to be created
c.
Syntax .. ${expression}… ex.. ${user.name}
d.
Expression language has some operators like +, - etc and relational operators &&
and || but it do not have full pledged programing language features like looping,
if-else etc
10.
JSTL (Java Standard Tag Library)
a.
Its standard tags used in JSP pages to control
the output of page display
b.
Conditional tags could be used to display menu
options based on user profile for example.
