servlets and jsp

Introduction
●

Q. What is J2EE ?
Java platform to developing enterprise web
application

Description
●

J2EE architecture : 3 tier
–

Client Tier ( Web tier)
●

–

Business Tier
●

–

The Presentation layer on the client side includes j2ee
componenets such as jsp,jsf etc
Components containing business logic of the
application such as Enterprise Beans.

Database Tier
●

This tier contains the persistence API of the application
so as to talk to database

Java Web Components
●

Servlet

●

Jsp ( Java Server Pages )

●

Jstl (Jsp Standard Tag Library)

●

Jsf ( Java Server Faces )

Servlet
●

Extends web server's functionality

●

Respond to Request from client

●

Used to generate dynamic response

●

Usually responses in HTML or Xml format

●

Most often used with HTTP protocol

Functioning of Servlet
●

●

●

Process or Store data that was submitted by
HTML forms
Provide dynamic content such as the result of
a database query
Manage State information
(in case of stateless HTTP protocol)

Packages (imports) for Servlet
●

java.io.*;
–

●

javax.servlet
–

●

Input and Output package (eg. Out.println)
Contains interaction logic between web container
and servlet

javax.servlet.http
–

Contains Http specific logic

●

javax.servlet.http.HttpServletRequest;

●

javax.servlet.http.HttpServletRespons

Servlet Skeleton
●

Imports

●

Public classname extends HttpServlet
–

Public void init()
●

–

Public void Service()
●

–

{ /* Initialization goes here */ }
{/* Business logic goes here */ }

Public void destroy()
●

{/* Free resources here */}

Lifecycle
●

Loaded and Instantiated

●

Initialization

●

Servicing the request

●

Destroying the request

●

Loaded and instantiated
–

●

Container loads servlet during startup or when the
request is made. After loading the servlet , the
container creates the instance of the servlet when
the first request come for service ,

Initialization
–

After creating the instance the container calls init()
method. The init method is called only once in
servlets lifetime. Initialization logic goes here

●

Servicing the request
–

After successful initialization , servlet will be
available to serve the request. Servlet creates
separate thread for each request

–

Service() method is called to serve the request
in short service method contains the business
logic

●

Destroying the servlet
–

If the servlet is no longer needed , the servlet
container calls the destroy() method.

–

Like the init() method destroy() method also get
called only once in servlet's lifetime

–

Destroy() method releases all the resources which
were acquired previously

JSP (Java Server Pages)
●

Jsp is a component which generates dynamic
contents

●

Jsp is a server-side technology

●

Extension : .jsp

●

Jsp usually consist of two components
–

Static Data
●

–

Can be expressed in any text based format such as
HTML

JSP elements
●

Jsp tags , which can generates dynamic contents

JSP Components
●

Declaration tag

●

Scriptlet tag

●

Expression tag

●

Directive tag

●

Action tag

●

Declaration tag:
–

Declaration is used to declare and define java
variables and methods inside your jsp

–

They are initialized when the jsp page is initialized

–

The scope of the declared variables or methods is
within the jsp page

–

Syntax : <%! int a = 10; %>

Declaration Example :
<html>
<body>
<%! int value = 10; %>
Hello World!<%= value %>
</body>
</html>

●

Scriptlet tag:
–

Scriptlets are block of java code

–

You can write any number of java code inside your
jsp using scriptlet

–

Syntax : <% ( Java Code ) %>

Scriptlet Example :
<html>
<body>
Hello World!
<%
out.println("Helloworld");
%>
</body>
</html>

●

Expression tag:
–

The code placed inside expression tag is printed
(output) , so there is no need to write out.println()

–

Mainly used to print values of variables and
methods

–

Syntax : <%= (variable or method) %>

Expression Example :
<html>
<body>
<%! int value = 10; %>
Hello World! <%= value %>
</body>
</html>

●

Directive tag:
–

Jsp directive provide directions and instructions to
the container , how to handle certain jsp
processing

–

There are 3 types of directives
●
●
●

Page directive
Include directive
Taglib directive

–

Page directive
●

●
●

Page directive is used to provide information about the
page
Example : <%@page language="java" %>
Here language is an attribute of the page directive

–

Include directive
●
●
●

Include is used to include a jsp file in the jsp page
Example : <%@ include file="/header.jsp" %>
File is an attribute which specifies which file need to
include

–

Taglib directive
●

●
●

Taglib directive is used to use the custom tags in the
jsp page ( custom tags allow us to define our own tags )
Example :
<%@ taglib uri="tlds/taglib.tld" prefix="mytag" %>

●

Action tag:
–

The action tag basically are used to control the
flow between pages and to use Java Beans

–

Some of the action tags are
●
●
●
●
●
●
●
●

Jsp:forward
Jsp:include
Jsp:useBean
Jsp:setProperty
Jsp:getPropery
Jsp:plugin
Jsp:param
Jsp:fallback

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