Session 36 - JSP - Part 1

Java & JEE Training
Session 36 – JSP Part 1

Classification: Restricted
Copyright @ 2000 Jordan Anastasiade. All rights reserved. 1
Agenda
• JSP (Java Server Pages Technology)
• JSP vs Servlet
• MVC Architecture
• Scriplet

JavaServer Pages Technology
• JavaServer Pages (JSP) technology provides a simplified, fast way to create
web pages that display dynamically-generated content.
• Server Page technology = the web pages are dynamically built on the server
side. E.g. JSP, ASP, BSP

JSP vs Servlet
Servlet = HTML in a Java class
JSP = Java in an HTML page
out.println(“<h1> Hello World! </h1>”);
<%= request.getParameter("title") %>

Model 1 Architecture

Model 2 Architecture
(also known as MVC or Model-View-Controller)
Single Responsibility Principle,
Separation of Concerns.

JSP Page
• A JSP page is a page created by the web developer that includes JSP
technology-specific tags, declarations, and possibly scriptlets, in
combination with other static HTML or XML tags.
• A JSP page has the extension .jsp; this signals to the web server that the JSP
engine will process elements on this page.
• Pages built using JSP technology are typically implemented using a
translation phase that is performed once, the first time the page is called.
The page is compiled into a Java Servlet class and remains in server
memory, so subsequent calls to the page have very fast response times.

Overview
• JavaServer Pages (JSP) lets you separate the dynamic part of your pages
from the static HTML.
HTML tags and text
<% some JSP code here %>
HTML tags and text
<I>
<%= request.getParameter("title") %>
</I>
You normally give your file a .jsp extension, and typically install it in any
place you could place a normal Web page

Client and Server with JSP

Translation Time
• A JSP application is usually a collection of JSP files, HTML files, graphics
and other resources.
• A JSP page is compiled when your user loads it into a Web browser
1. When the user loads the page for the first time, the files that make up the
application are all translated together, without any dynamic data, into
one Java source file (a .java file)
2. The .java file is compiled to a .class file. In most implementations, the
.java file is a Java servlet that complies with the Java Servlet API.

Simple JSP Page
<%@ page info=“A Simple JSP Sample” %>
<HTML>
<H1> First JSP Page </H1>
<BODY>
<% out.println(“Welcome to JSP world”); %>
</BODY>
</HTML>

How JSP Works?
User Request – JSP File Requested
Server
File
ChangedCreate Source from JSP
Compile Execute Servlet

Review of Life Cycle of Servlet

JSP Lifecycle
1.Translation (JSP
 Servlet)
2.Compilation
(Servlet
compiled)
3.Loading
4.Instantiation
5.Initialization
6.Request
Processing
7.Destruction

JSP Elements
• Declarations <%! code %>
• Expressions <%= expression %>
• Scriptlets <% code %>

HTML Comment
• Generates a comment that is sent to the client.
• Syntax

• Example:

Declaration
• Declares a variable or method valid in the scripting language used in the JSP page.
• Syntax
<%! declaration; [ declaration; ]+ ... %>
• Examples
<%! String destin; %>
<%! public String getDestination()
{return destin;}%>
<%! Circle a = new Circle(2.0); %>
• You can declare any number of variables or methods within one declaration
element, as long as you end each declaration with a semicolon.
• The declaration must be valid in the Java programming language.

Declaration Example: Variables declaration
<HTML>
<HEAD><TITLE>JSP Declarations</TITLE></HEAD>
<BODY><H1>JSP Declarations</H1>
<%! private int keepCount = 0; %>
<H2>
Page accessed:
<%= ++keepCount %>
times
</H2>
</BODY>
</HTML>
Best Practice: Never use instance
variables in Servlets. (Multithreading)

Declaration example: Methods declaration
<html>
<head>
<title>Methods Declaration</title>
</head>
<body>
<%!
int sum(int num1, int num2, int num3){
return num1+num2+num3;
}
%>
<%= "Result is: " + sum(10,40,50) %>
</body>
</html>

Predefined Variable – Implicit Objects
• request – Object of HttpServletRequest (request parameters, HTTP headers, cookies
• response – Object of HttpServletResponse
• out - Object of PrintWriter buffered version JspWriter
• session - Object of HttpSession associated with the request
• application - Object of ServletContext shared by all servlets in the engine
• config - Object of ServletConfig
• pageContext - Object of PageContext in JSP for a single point of access
e.g. pageContext.getSession()
• page – variable synonym for this object
e.g. <%= ((Servlet)page).getServletInfo () %>

Expression
• Contains an expression valid in the scripting language used in the JSP page. Syntax:
<%= expression %>
<%! String name = new String(“JSP World”); %>
<%! public String getName() { return name; } %>
<B><%= getName() %></B>
• Description:
An expression element contains a scripting language expression that is
evaluated, converted to a String, and inserted where the expression appears in
the JSP file.
• Because the value of an expression is converted to a String, you can use an
expression within a line of text, whether or not it is tagged with HTML, in a
JSPfile. Expressions are evaluated from left to right.

Expression Example
<HTML>
<HEAD>
<TITLE>JSP Expressions</TITLE>
</HEAD>
<BODY>
<H2>JSP Expressions</H2>
<UL>
<LI>Current time: <%= new java.util.Date() %>
<LI>Your hostname: <%= request.getRemoteHost()%>
<LI>Your session ID: <%= session.getId() %>
</UL>
</BODY>
</HTML>

Expression Example 2
<html>
<head>
<title>JSP expression tag example1</title>
</head>
<body>
<%= 2+4*5 %>
</body>
</html>

<html>
<head>
<title>JSP expression tag example2</title>
</head>
<body>
<%
int a=10;
int b=20;
int c=30;
%>
<%= a+b+c %>
</body>
</html>

index.jsp
<html>
<head>
<title> JSP expression tag example3 </title>
</head>
<body>
<% application.setAttribute("MyName", "Chaitanya"); %>
<a href="display.jsp">Click here for display</a>
</body>
</html>
display.jsp
<html>
<head>
<title>Display Page</title>
</head>
<body>
<%="This is a String" %><br>
<%= application.getAttribute("MyName") %>
</body>
</html>

Scriptlet
• Contains a code fragment valid in the page scripting language.
• Syntax
<% code fragment %>
<%
String var1 = request.getParameter("name");
out.println(var1);
%>
• This code will be placed in the generated servlet method:
_jspService()

Scriplet Example
<HTML>
<HEAD><TITLE>Weather</TITLE></HEAD>
<BODY>
<H2>Today's weather</H2>
<% if (Math.random() < 0.5) { %>
Today will be a <B>sunny</B> day!
<% } else { %>
Today will be a <B>windy</B> day!
<% } %>
</BODY>
</HTML>

Topics to be covered in next session
• JSP vs Servlet
• LifeCycle of Servlet
• JSP Elements
• JSP Page directive
• Directives vs Action tags

Thank you!

Session 36 - JSP - Part 1

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Session 36 - JSP - Part 1