Embed Size (px)
Citation preview
Web TechnologiesJava Beans & JSP
ByPraveen Kumar G
April 22, 2023 © 2006 IIITM-K 2
Java Beans
What Are Beans?
Beans are standard java objects.
• Must have a zero-arguments constructor.• Should have no public fields.• Values should be accessed through method calls,
getXxx, setXxx & isXxx.
April 22, 2023 © 2006 IIITM-K 3
Java Bean (example)
public class Person {private int age;private String name;… … …public void setAge(int age){
this.age = age;}public void setName(String name){
this.name = name;}public int getAge(){
return this.age;}public String getName(){
return this.name;}
… … …}
April 22, 2023 © 2006 IIITM-K 4
Java Server Pages
• Overview of JSP Technology• JSP Scripting Elements• JSP Page Directives
April 22, 2023 © 2006 IIITM-K 5
Overview of JSP Technology
• What is JSP• The need for JSP• The benefits of JSP• Advantages over other
technologies• Location of JSP pages
April 22, 2023 © 2006 IIITM-K 6
What is JSP
• Servlets – HTML in java code• JSP – java code in HTML
<HTML>
<HEAD><TITLE>Java Server Pages</TITLE></HEAD>
<BODY>
<H1>JSP</H1>
<%= “Java Server Pages.” %>
<HR>
</BODY>
</HTML>
April 22, 2023 © 2006 IIITM-K 7
JSP Lifecycle
JSP to ServletTranslation
JSP to ServletTranslation
ServletCompiled
ServletCompiled
ServletLoaded
ServletLoaded
jspInit()called
jspInit()called
_jspService()called
_jspService()called
April 22, 2023 © 2006 IIITM-K 8
The need for JSP
With servlets•It is hard to write and maintain
HTML•Cannot use standard HTML tools•HTML is inaccessible to non-java
developers
April 22, 2023 © 2006 IIITM-K 9
The benefits of JSP
• Easier to write and maintain HTML• Can use standard HTML tools• Can divide up development team
April 22, 2023 © 2006 IIITM-K 10
Advantages
• The Java advantage• Extensive API• Easy to learn• Big development community• Standardization & server support
April 22, 2023 © 2006 IIITM-K 11
Location of JSP pages
Unlike servlets, JSP pages can be located in any of the locations where HTML files can be put.
April 22, 2023 © 2006 IIITM-K 12
JSP Scripting Elements
JSP scripting elements enable us to insert java code into JSP files.
There are three types –•Expressions <%= Java Expression %>
•Scriptlets <% Java Code %>
•Declarations <%! Field/Method %>
April 22, 2023 © 2006 IIITM-K 13
JSP Expressions
A JSP expression is used to insert java code directly into the output.Have the following form
<%= Expression %>Eg:
Current Time: <%= new java.util.Date() %>Op:
Current Time: Tue Aug 22 21:05:47 IST 2006
The expression is evaluated, converted to string and inserted into the page.
April 22, 2023 © 2006 IIITM-K 14
Predefined Variables• To simplify expressions, JSP provides a
number of predefined variables (implicit objects).
• request – the HttpServletRequest• response – the HttpServletResponse• session – the HttpSession• out – the Writer (buffered version of type
JspWriter)
• application – the ServletContext• config – the ServletConfig• pageContext – introduced to give single point
of access to page attributes• page – synonym for “this”
April 22, 2023 © 2006 IIITM-K 15
JSP Scriptlets• To something more than just output the
value of a simple expression.• Allows the programmer to insert
arbitrary code into the servlets _jspService method.
• Have the following form:<% Java Code %>
Eg:
<%
String str = request.getParameter(“name”);
out.print(“Name : ”+str);
%>
April 22, 2023 © 2006 IIITM-K 16
JSP Declarations• JSP declarations lets the programmer
define methods or fields that get inserted into the main body of the generated servlet (outside the _jspService() method)
• Have the following form:<%! Field/Method definition %>
Eg:<%!
private String getMessage(){return “This is a simple message!!”;
}%><%= getMessage() %>
April 22, 2023 © 2006 IIITM-K 17
XML Syntax
• XML like syntax for JSP expression, scriptlet & declaration<jsp:expression>…</jsp:expression>
<jsp:scriptlet>…</jsp:scriptlet>
<jsp:declaration>…</jsp:declaration>
• Supported by JSP versio 1.2 & above
• These are case sensitive, should be in lowercase
April 22, 2023 © 2006 IIITM-K 18
JSP Directives
A JSP directive affects the overall structure of the servlet that results from the JSP page.
A JSP directive has the form:<%@ directive attribute=“value” … … %>
There are three types:page, include & taglib
April 22, 2023 © 2006 IIITM-K 19
JSP Page Directive
The page directive controls the structure of the servlet by importing classes, customizing the superclass, changing content type, etc.The JSP Page directive has the following attributes:import, contentType, pageEncoding, session,isELIgnored, buffer, autoFlush, info, errorPage, isThreadSafe, language & extends
April 22, 2023 © 2006 IIITM-K 20
JSP Page Directive Attributes
import=“java.util.*, java.sql.*”
contentType=“text/html; charset=ISO-8859-1 ”pageEncoding=“Shift_JIS”
session=“true/false”
isELIgnored=“false/true”
buffer=“size in kb”
autoFlush=“true/false”
info=“Some info message.”
errorPage=“error.jsp”
isErrorPage=“false/true”
isThreadSafe=“true/false”
language=“java”
extends=“package.class”
org.apache.jasper.runtime.HttpJspBase
javax.servlet.jsp.HttpJspPage
org.apache.jasper.runtime.HttpJspBase
javax.servlet.jsp.HttpJspPage
April 22, 2023 © 2006 IIITM-K 21
Including Files
There are three ways of including external files into a JSP document.
<jsp:include …>…
<%@ include …>
<jsp:plugin …>…
April 22, 2023 © 2006 IIITM-K 22
The jsp:include Action
This includes the output of a secondary page at the time the main page is requested.
The output of the sub page must be HTML generated by a servlet or JSP.<jsp:include page=“/inc/header.jsp” flush=“true” />
<jsp:include page=“/inc/header.jsp” flush=“true”>
<jsp:param name=“paramName” value=“xyz”>
</jsp:include>
April 22, 2023 © 2006 IIITM-K 23
The Include Directive
This includes directive is used to include a file in the main JSP at the time of translation into a servlet.
The code of the included file is added to that of the JSP document.<%@ include page=“/inc/header.jsp” %>
April 22, 2023 © 2006 IIITM-K 24
Forwarding Requests
This action is used to get the output of a JSP file completely from another JSP or servlet.
The output of the auxiliary JSP or servlet is sent to the client, not that of the current JSP.
<jsp:forward page=“xyz.jsp” />
April 22, 2023 © 2006 IIITM-K 25
The jsp:plugin Action
Used to embed a java applet into the generated output.
Java applets are rarely used in web pages now a days.<jsp:plugin type=“applet”
code=“MyApplet.class”
width=“400” height=“300”>
</jsp:plugin>
April 22, 2023 © 2006 IIITM-K 26
jsp:plugin Attributestype=“applet” bean can also be used.
Code=“MyApplet.class”
width=“…”
height=“…”
codebase=“base directory for the applet”
align=“…” laet, right, top, bottom or middle
hspace=“…”
vspace=“…”
archive=“specify JAR file”
title=“Title for the Applet”
jreversion=“1.2”
iepluginurl=“…”
nspluginurl=“…”
April 22, 2023 © 2006 IIITM-K 27
jsp:plugin Parameters & Fallback
<jsp:plugin type=“applet”
code=“MyApplet.class”
width=“400” height=“300”>
<jsp:params>
<jsp:param name=“P1” value=“xyz” />
<jsp:param name=“P2” value=“abc” />
</jsp:params>
<jsp:fallback>
<b>Java Plugin needed.</b>
</jsp:fallback>
</jsp:plugin>
April 22, 2023 © 2006 IIITM-K 28
Using Java Beans & JSP
There are three main constructs to use Java Beans in JSP.
<jsp:useBean ……… />
<jsp:getProperty ……… />
<jsp:setProperty ……… />
April 22, 2023 © 2006 IIITM-K 29
jsp:useBean
Used to load a bean to be used in the JSP document.
Syntax: <jsp:useBean id=“name” class=“package.Class” />
Eg: <jsp:useBean id=“person” class=“iiitmk.Person” />
Equivalent to: <% iiitmk.Person person = new iiitmk.Person(); %>
April 22, 2023 © 2006 IIITM-K 30
Getting bean properties
Used to read properties from beans.
Syntax: <jsp:getProperty id=“name” property=“propName” />
Eg: <jsp:getProperty id=“person” property=“name” />
Equivalent to: <%= person.getName() %>
April 22, 2023 © 2006 IIITM-K 31
Setting bean properties
Used to set properties of beans.
Syntax: <jsp:setProperty id=“name” property=“propName”
value=“propValue” />
Eg: <jsp:setProperty id=“person” property=“name”
value=“Popeye The Sailor” />
Equivalent to: <% person.setName(“Popeye The Sailor”); %>
April 22, 2023 © 2006 IIITM-K 32
Properties & Request Parameters
The value of a bean property can be set directly from the value of the corresponding request parameter.
Syntax: <jsp:setProperty id=“name” property=“propName”
param=“propName” />
Eg: <jsp:setProperty id=“person” property=“name”
param=“name” />
<jsp:setProperty id=“person” property=“*” />
April 22, 2023 © 2006 IIITM-K 33
Sharing Beans (scope)
The scope of a bean defines where the bean is stored and how it is accessible. By default it is accessible as a local variable. Other places of storing beans are the request, session and application.Syntax: <jsp:useBean … … … scope=“…” />
Scopes:
page, request, session & application
April 22, 2023 © 2006 IIITM-K 34
Page Scope
The default scope of a bean. Bean is bound to a local variable in the _jspService method and also placed in the pageContext predefined variable, accessible by calling getAttribute() method.Syntax: <jsp:useBean … … … scope=“page” /> <jsp:useBean … … … />
April 22, 2023 © 2006 IIITM-K 35
Request Scope
In addition to being bound to a local variable, the bean is also placed in the HttpServletRequest object (request) for the duration of the current request.Accessible by getAttribute() method.Syntax: <jsp:useBean … … … scope=“request” />
April 22, 2023 © 2006 IIITM-K 36
Session Scope
In addition to being bound to a local variable, the bean is also placed in the HttpSession object (session).Accessible by getAttribute() method.
Syntax: <jsp:useBean … … … scope=“session” />
April 22, 2023 © 2006 IIITM-K 37
Application Scope
In addition to being bound to a local variable, the bean is also placed in the ServletContext object (application). The servlet context is shared by all the JSP and servlets in the webapplication.Accessible by getAttribute() method.
Syntax: <jsp:useBean … … … scope=“application” />
Questions ?
