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Java Server Pages
Jeffrey Jongko
Introduction

Java Server Pages (JSP) technology was
created by Sun Microsystems and is built
on top of Sun’s Java Servlet technology

Java Servlets was Sun’s first answer for
developing web-based applications use
the Java programming language.
Introduction

Java Servlet technology suffered similar
maintenance problems that many traditional
web-technologies like CGI had (presentation and
logic are combined)

JSP is designed to facilitate development of
dynamic web sites by more easily dissociating
presentation from application logic
– allowing page developers to develop page
presentation without interfering with application logic
development
JSP Architecture

The purpose of JSP is to provide a
declarative, presentation-centric method
of developing servlets.

JSP specification is defined as a standard
extension on top the Servlet API.

Consequently, it should not be too
surprisingly that under the covers, servlets
and JSP pages have a lot in common.
JSP Architecture

Typically, JSP pages exist as simple text
files and are subject to a translation phase
and a request processing phase.

The translation phase is carried out only
once, unless the JSP page changes, in
which case it is repeated.
– The JSP page is transformed into a servlet
which subsequently processes all future
requests to the page
JSP Architecture
Sample JSP file
<html>
<body>
<center>
<%
String hello = "Hello World";
%>
<h1><%= hello %></h1>
</center>
</body>
</html>

The following JSP file is
saved to a file
HelloWorld.jsp

It looks like regular
HTML will special
regions delimited with
special markers like
“<%” and “%>” which
represent JSP features
JSP Syntax core elements

There are four basic core elements in JSP
– comments
– declarations
– expressions
– scriptlets
JSP Comments

There are 2 types of JSP comments
– HTML comment
– Hidden comment
HTML Comment Syntax


Hidden Comment Syntax
<%-- comment --%>


A JSP HTML comment is a comment that is sent to the
client (appears on the page data)

JSP expressions (seen later) can be included inside an
HTML comment
Sample JSP Comments
<html>
<body>
<%@ page import="java.util.*" %>
<%@ page import="java.text.*" %>

<%
String hello = "Hello World";
%>
<h1><%= hello %></h1>
<%-- This will not appear --%>
</body>
</html>
DATA RECEIVED BY CLIENT:
<html>
<body>

<h1>Hello World</h1>
</body>
</html>
JSP Declarations

JSP Declarations are used to define variables
and methods that are visible to the whole page
– variables are translated into an instance variable in
the compiled servlet
JSP Declaration Syntax
<%! variable / method declaration %>


Variables declared in this way are not threadsafe. The JSP page has to be declared as
single-threaded if thread safety is needed for
these variables.
Sample JSP Declaration
<%!
int counter = 0;
boolean isSameString(String a,
String b)
{
return a.equals(b);
}
%>
<html>
<body> bjlee and hjk is
<%= (isSameString(“bjlee”,”hjk”))
? ”” : ”not” %>
same string
</body>
</html>
OUTPUT ON CLIENT:
<html>
<body>
bjlee and hjk is not same string
</body>
</html>
JSP Expressions

Scripting language expression that is
evaluated and converted into a String for
insertion into the output page
JSP Expression Syntax
<%= variable / method call %>

Sample JSP Expressions
<html>
<body>
<%@ page import="java.util.*" %>
<%@ page import="java.text.*" %>

<%
String hello = "Hello World";
%>
<h1><%= hello %></h1>
<%-- This will not appear --%>
</body>
</html>
DATA RECEIVED BY CLIENT:
<html>
<body>

<h1>Hello World</h1>
</body>
</html>
JSP Scriptlets

Scripting language code fragment that is
run within the service() method of the
compiled servlet
– variables declared within a scriptlet are local
unlike those declared by JSP Declarations
JSP Scriptlet Syntax
<% scripting language code %>

Sample JSP Scriptlet
<%@ page import=“java.util.*”%>
<html><body bgcolor=“white”>
<%
String name = “Byung Joon Lee”;
StringTokenizer st=
new StringTokenizer(name, “ “);
while ( st.hasMoreTokens() )
{
%>
<%= st.nextToken() %> <BR>
<%
}
%>
</body></html>
OUTPUT ON CLIENT:
<html><bodybgcolor=“white”>
Byung<BR>
Joon<BR>
Lee<BR>
</body></html>
<%@page %> Directive

<%@page %> directive defines attributes that
apply to a whole JSP page

Example of some attributes:
[
[
[
[
[
[
[
[
language=“java”]
extends=“package.class”]
import=“{package.class | package.*}, ...”]
session=“true|false”]
isThreadSafe=“true|false”]
info=“text”]
errorPage=“relativeURL”]
isErrorPage=“true|false”]
Implicit Objects

Data is passed to JSP pages from the outside via
HTTP POST or GET

This data is accessed via an implicit object
– the name of this object is called request of type
javax.servlet.ServletRequest
– implicit objects are accessed via the scriptlets

Other implicit objects exist such as
–
–
–
–
response of type javax.servlet.ServletResponse
pageContext
session
application
Other JSP features

Ability to access JavaBean components
using JSP tags, e.g.
– <jsp:useBean>
– <jsp:setProperty>
– <jsp:getProperty>

This allows access to JavaBean objects
without the use of scriptlets/Java code
Other JSP features

Ability to extend the usable JSP tags using a
custom tag library
– this is used to reduce the number of scriptlets on the
page by encapsulating their logic behind tags.

Both these features reduce the need for people
with actual Java language experience which is
needed for coding scriptlets
– allows for the development of presentation (JSP
page) and the actual business logic (JavaBeans) to
developed separately
Sites

Some sites that use Java Server Pages
– http://www.sun.com
– http://www.friendster.com
References
http://java.sun.com/products/jsp/
 http://www.swpark.pe.kr/lecture/jsp.pdf
 http://developer.java.sun.com/developer/o
nlineTraining/JSPIntro/
 http://archive.coreservlets.com


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