Transcript Java Server Pages

Java Server Pages
B.Ramamurthy
Topics for Discussion
Inheritance and Polymorphism
Develop an example for inheritance and
polymorphism
JSP fundamentals
JSP Examples with Netbeans
Finish the semantic web topic
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Java Server Pages
Servlets are pure Java programs. They introduce
dynamism into web pages by using programmatic
content.
JSP technology is an extension/wrapper over the
Java servlet technology.
JSP are text based documents.
We will focus only on JSP since it subsumes the
servlet technology.
Two major components of JSP:
 Static content: provided by HTML or XML
 Dynamic content: generated by JSP tags and
scriplets written in Java language to encapsulate
the application logic and XHTML.
JSP compilation into Servlets
JSP
Initial
request
Web
Browser
Web
Server
J2EE Web
Container
translation
Java
Subseq
request Servlets
Servlets
Client-server model: Client requests
something of a server and the server
performs action(s) and responds to the client.
This request-response model is the highest
level of networking in Java.
A servlet extends the functionality of a server.
javax.servlet and javax.servlet.http package
provide the classes and interfaces to define
servlets.
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What are servlets?
Servlets are server side
components/programs that are primarily
designed to use with HTTP protocol.
~ provide secure access to a Website and to
interact with databases on behalf of a client.
~ dynamically create HTML documents to be
displayed by the browser.
~ can maintain unique session information
for each client.
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Support for servlets
Servlets are to servers what applets are
to a client (web browser).
Servlets are normally executed of a web
server.
Many web servers support servlets:
Glassfish, Apache Tomcat, IIS.
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Servlet API
It is good programming practice to start the
design/definition with an interface.
Conversely interfaces are good starting point
to study an API.
Servlet interface:
void init (ServletConfig config)
ServletConfig getServletConfig()
void service (ServletRequest req, ServletResponse res)
String getServletInfo()
void destroy()
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Servlet API
Servlet interface is implemented by two
abstract classes GenericServlet and
HTTPServlet.
HTTPServlet is for interfacing with HTTP
protocol and we will look at only this in
our discussion today.
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HTTPServlet
Two most common HTTP requests are GET
and POST.
GET request gets information from the
server. For example: retrieve an image or
document.
POST requests are to send to the server the
information from a HTML form which a client
enters. For example: request to search
internet, query database, send authentication
information.
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HTTPServlet Methods
service: This is called when a request arrives at a
server. This method in turn calls doXYZ.
doGet : responds to HTTP GET ; get information to
browser
doPOST: responds to HTTP POST : send request to
server
doDelete : responds to HTTP DELETE : to delete a file
on server!
doOptions : responds to HTTP OPTIONS
doPut : responds to HTTP PUT : to save a file
doTrace: called in response to HTTP TRACE for
debugging purposes
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Your Servelet
Your servlet will typically extend class
HTTPServlet.
You will override doGet, doPost and
anyother methods of HTTPServlet.
Place it n webpages/WEB-INF/servlets
Example:/web/faculty/bina/webpages/WEB-INF/servlets
Html file acessing the servlet in your regular web
pages home.
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Servlet Semantics
The webserver that executes that executes a
servlet creates an HTTPServletRequest object
and passes it to the servlet’s service method
which in turn passes it to doGet.
This object contains request from the client.
Webserver executes the request and creates
HTTPServletResponse object and passes this
to the client using doPOST.
The object contains response to the client’s
request.
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HTTPServletRequest
String getParameter (String name)
Enumeration getParameterNames()
String[] getParameterValues(String name)
Cookie[] getCookies()
HttpSession getSession(boolean create)
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HTTPServletResponse
void addCookie(Cookie cookie)
ServletOutputStream getOutputStream()
PrintWriter getWriter()
void setContentType(String type)
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More on JSP syntax and
contents
HTML code for user interface lay out
JSP tags: declarations, actions, directives,
expressions, scriplets
JSP implicit objects: a request object,
response object, session object, config object
Javabeans: for logic that can be taken care of
at the JSP level.
We will examine only JSP tags here.
JSP Tags
Declaration: variable declaration
<%! int age = 56 %>
Directive: ex: import classes
<%@ page import = “java.util.*” %>
Scriplet: Java code
<% if password(“xyz”) {
%>
<H1> Welcome <\H1>
Expression: regular expression using variables
and constants
 <%= param[3]+4 %>
Action: <jsp:usebean name =“cart”
class=“com.sun.java.cart”
Java Server Pages by
Examples
JSPs combine static markup (HTML, XML)
with special dynamic scripting tags.
Each JSP is translated into a servlet the first
time it is invoked. Then on, the requests are
serviced by the servlets.
Lets understand the building blocks of a JSP,
namely, directives, scripting elements, and
actions through a series of examples.
Examples: Directives
<%@
%>
A directive configures the code generation
that container will perform in creating a
servlet.
Simple JSP showing access to a Java API
class Date: simple.jsp
Using Page directives to define various page
attributes: pageDirective.jsp
Directive to include other JSPs:
includeDirective1.jsp, includeDirective2.jsp
Examples: Scripting Elements
Declaration:
<%!
%>
A declaration is a block of code in a JSP
that is used to define class-wide
variables and methods in the generated
servlet.
Declaring a piece of code:
declaration.jsp
Examples: Scripting Elements
(contd.)
Scriplets: <% %>
A scriplet is a block of Java code that is
executed during the request-processing time.
See scriplet.jsp
Expressions: sends a value of a Java
expression back to the client.
<%= %>
See expression.jsp
Examples: Standard Actions
Standard actions are well known tags that
affect the run time behavior of the JSP and
the response sent back to the client.
Some commonly used tag actions types are:
<jsp:useBean>
<jsp:setProperty>
<jsp:getProperty>
<jsp:param>
<jsp:include>
<jsp:forward>
<jsp:plugin>