Core web application development

Core Web Application
Development Using Servlet &
JSP
Bahaa Farouk
Organized
By

Agenda
• Servlet
– What is Java Servlet?
– Servlet Life Cycle
– Client Interaction & Session
• JSP
– What’s JSP?
– JSP Life Cycle
– What’s JSP Contains?
– JSP Scope & Implicit Objects
• Why Servlet & JSP?

What is Java Servlet?
• An alternate form of server-side computation that
uses Java
• The Web server is extended to support an API, and
then Java programs use the API to create dynamic
web pages
• Using Java servlets provides a platform-independent
replacement for CGI scripts.
• Servlets can be embedded in many different servers
because the servlet API, which you use to write
servlets, assumes nothing about the server's
environment or protocol.

Servlet Life Cycle
• Initialization
– the servlet engine loads the servlet’s *.class file in the JVM
memory space and initializes any objects
• Execution
– when a servlet request is made,
• a ServletRequest object is sent with all information about the
request
• a ServletResponse object is used to return the response
• Destruction
– the servlet cleans up allocated resources and shuts down

Client Interaction
• When a servlet accepts a call from a client,
it receives two objects:
– A ServletRequest, which encapsulates the
communication from the client to the server.
– A ServletResponse, which encapsulates the
communication from the servlet back to the
client.
• ServletRequest and ServletResponse are
interfaces defined by the javax.servlet
package.

Session Capabilities
• Session tracking is a mechanism that servlets use to
maintain state about a series of requests from the
same user(that is, requests originating from the
same browser) across some period of time.
• Session tracking capabilities. The servlet writer can
use these APIs to maintain state between the servlet
and the client that persists across multiple
connections during some time period.

What is JSP?
• A Java Servlet is a Java program that is run on the
server
– There are Java classes for retrieving HTTP requests and
returning HTTP responses
– Must return an entire HTML page, so all tuning of the page
must be done in a Java program that needs to be re-
compiled
• Java Server Pages (JSP)
– use HTML and XML tags to design the page and JSP scriplet
tags to generate dynamic content (Easier for separation
between designer & developer)
– use Java Beans and useful built-in objects for more
convenience

JSP Life Cycle
• JSP page (MyFirstJSP.jsp)
– Translated to Servle (MyFirstJSP.servlet)
– Compiled to class (MyFirstJSP.class)
– Loaded into memory (Initialization)
– Execution (repeats)
– Destruction

• Any change in JSP page automatically repeats the
whole life cycle.

Introduction
• A Java Servlet is a Java program that is run on the
server
– There are Java classes for retrieving HTTP requests and
returning HTTP responses
• Java Server Pages (JSP)
– use HTML and XML tags to design the page and JSP scriplet
tags to generate dynamic content
– use Java Beans, which are reusable components that are
invoked by scriplets

What do JSPs contain?
• Template data
– Everything other than elements (eg. Html tags)
• Elements
– based on XML syntax
• <somejsptag attribute name=“atrribute value”> BODY
</somejsptag>
– Directives
– Scripting
• Declarations
• Scriptles
• Expressions
– Standard Actions

Directives
• <%@ directivename attribute=“value”
attribute=“value” %>
• The page directive
– <%@ page ATTRIBUTES %>
– language, import, Buffer, errorPage,…
– <%@ page languange=“java”
import=“java.rmi.*,java.util.*” %>
• The include directive
– <%@ include file=“Filename” %>
– the static file name to include (included at translation
time)
• The taglib directive
– <% taglib uri=“taglibraryURI” prefix=“tagPrefix” %>

Scripting
(Declaration, Expressions, Scriptlets)
• <%! . . %> declares variables or methods
– define class-wide variables
– <%! int i = 0; %>
– <%! int a, b; double c: %>
– <%! Circle a = new Circle(2.0); %>
– You must declare a variable or method in a jsp page before
you use it
– The scope of a declaration is the jsp file, extending to all
includes

• <%= . . %> defines an expression and casts the result
as a string

Scripting II
• <%= . . %> can contain any language expression, but
without a semicolon, e.g.
• <%= Math.sqrt(2) %>
• <%= items[I] %>
• <%= a + b + c %>
• <%= new java.util.Date() %>
• <% . . %> can handle declarations (page scope),
expressions, or any other type of code fragment
• <% for(int I = 0; I < 10; I++) {
out.println(“<B> Hello World: “ + I); } %>

JSP and Scope
• Page - objects with page scope are accessible only within the
page where they are created
• Request - objects with request scope are accessible from
pages processing the same request where they were created
• Session - ojbects with session scope are accessible from pages
processing requests that are in the same session as the one in
which they were created
• Application - objects with application scope are accessible
from pages processing requests that are in the same
application as the one in which they were created
• All the different scopes behave as a single name space

Implicit Objects
• These objects do not need to be declared or instantiated by
the JSP author, but are provided by the container (jsp engine)
in the implementation class
• request Object (javax.servlet.ServletRequest)
• response Object (javax.servlet.ServletResponse)
• session Object (javax.servlet.http.HttpSession)
• application Object
• out Object
• config Object
• page Object
• pageContext Object (javax.servlet.jsp.PageContext)
• exception

Why Servlet/JSP?
What is an Enterprise Application?
• Reliable
• Scalable
• Maintainable
• Manageable

– If you are developing an Enterprise Application for
whose daily transactions are millions?
• Performance? Scalability? Reliability?

Core web application development

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