Jsp element

Chapter 2

JSP Element

http://www.java2all.com

JSP Element


In previous example described in introduction
to JSP, We didn`t use any java statement or code in
the file. If the developer wants to put any java code
in that file then the developer can put it by the use
of jsp tags(elements).

There are mainly three group of jsp
tags(elements) available in java server page :
1 ) JSP Scripting elements
2 ) JSP Directive elements
3 ) JSP Standard Action elements
All three elements described in next three topic.

JSP Scripting elements


1. JSP Scripting elements :

There are four types of tag in jsp scripting
elements.

a) JSP Declaration tag.

b) JSP scriptlet tag.

c) JSP Expression tag.

d) Comment tag.

Now we describe each tag in detail. http://www.java2all.com

a) JSP Declaration tag :

A JSP declaration lets you declare or define
variables and methods (fields) that use into the jsp
page.

Declaration tag Start with <%! And End with
%>
The Code placed inside this tag must end with a
semicolon (;).

Syntax: <%! Java Code; %>

<%! private int i = 10; %>
<%! private int squre(int i)
{
i=i*i;
return i;
}
%>

You can also put these codes in a single syntax
block of declaration like,
<%! private int i = 10;
private int squre(int i)
{
i=i*i;
return i;
}
%>

Note : The XML authors can use an alternative
syntax for JSP declaration tag:

<jsp:declaration>
Java code;
</jsp:declaration>

EX.
<jsp:declaration> private int i = 1; </jsp:declaration>
<jsp:declaration>
{
i=i*i;
return i;
}
</jsp:declaration>

You can also put these codes in a single syntax block of
declaration like,
<jsp:declaration>
private int i = 1;
{
i=i*i;
return i;
}
</jsp:declaration>

Remember that XML elements, unlike HTML
ones, are case sensitive. So be sure to use lowercase.

Declarations do not generate any output so the
developer uses declaration tag with JSP expression tag
or JSP scriptlet tag for generating an appropriate
output for display it in the appropriate browser.


b) JSP scriptlet tag :

A JSP scriptlet lets you declare or define any
java code that use into the jsp page.

scriptlet tag Start with <% and End with
%>

The Code placed inside this tag must end
with a semicolon (;).

Syntax: <% Java Code; %>

EX.
<%
int a = 10;
out.print("a ="+a);
%>

syntax for JSP scriptlet tag.
<jsp:scriptlet>
Java code;
</jsp:scriptlet>

c) JSP Expression tag :

A JSP expression is used to insert Java values directly
into the output.

JSP Expression tag is use for evaluating any expression
and directly displays the output in appropriate web browser.

Expression tag Start with <%= and End with %>

The Code placed inside this tag not end with a
semicolon (;).

Syntax: <%= Java Code %>

For example. the following shows the date/time
that the page was requested:

Current time: <%= new java.util.Date() %>

syntax for JSP expressions:

<jsp:expression>
Java Expression
</jsp:expression>

d) Comment tag :

Although you can always include HTML
comments in JSP pages, users can view these if they
view the page's source. If you don't want users to be
able to see your comments, embed them within the <
%-- ... --%> tag.
<html>
<head>
<title>Comment demo</title>
</head>
<body>
This is simple demo of test the comment 

<%-- This is a comment. Comments are not displayed in the browser as well as not displayed in view
source also --%>
</body>
</html>

Output :
This is simple demo of test the comment.

Now right click on the browser and select the
view source so we can get the code in Notepad like,
<html>
<head>
<title>Comment demo page</title>
</head>
<body>
This is simple demo of test the comment. 

</body>
</html>

In the view sorce code, the comment put in <%--
comment --%> will not display but the comment put
in <!—comment will display.

Now using these JSP Scripting elements, we are developing some
simple examples so the use of these tags can easily understood.
<html>
<head>
<title>Scripting Demo page</title>
</head>
<body>
<%-- declaration tag --%>
<%! int i = 10; %>

<%-- scriptlet tag --%>
<% out.print("i = "+i); %>
 
 
<% out.print("for loop execution start..........."); %>
 
<%
for(int j=1;j<=10;j++)
{
out.print("j = "+j);
%>
 
<%
}

out.print("for loop execution complete...........");
%>
 
 

<%-- expression tag --%>
<%! int a = 10;
int b = 20;
%>
The addition of two variable : a + b = 10 + 20 = <%= a+b %>
 
 
Current time : <%= new java.util.Date() %>
</body>
</html

Output :
i = 10
for loop execution start...........
j=1
j=2
j=3
j=4
j=5
j=6
j=7
j=8
j=9
j = 10
for loop execution complete...........
The addition of two variable : a + b = 10 + 20 = 30
Current time : Sun Feb 12 14:00:35 IST 2012


JSP Directive elements


2. JSP Directive elements :

A JSP directive gives special information about
the page to JSP Engine.

Each JSP goes through two phases:

(1) The first phase is known as translation time,
during which the JSP engine turns the file into
a servlet. (The step following from 1 to 5 in JSP
Architecture)


• The second phase is known as request time,
during which the resulting servlet is run to
actually generate the page. (The step following
from 6 to 9 in JSP Architecture)

The JSP engine handles the directives at translation
time because the JSP engine will translate a
particular directive into a servlet only for the first
time so the developer can get more speed for the
process of loading a JSP file in a future.
Syntax:

<%@ directive-name [attribute=”value”
attribute=”value”………….] %> http://www.java2all.com

Note : The XML syntax for defining directives
is
<jsp:directive.directiveType [attribute=”value”
attribute=”value”………….] /> Three main types of
directives are:

a) page directive

b) include directive

c) taglib directive

a) page directive :

The page directive is used to specify attributes
for the JSP page as a whole.

The page directive does not produce any
visible output when the page is requested but
change the way the JSP Engine processes the
page.

e.g., you can make session data unavailable to
a page by setting a session to FALSE.


Syntax:

<@ page [attribute=”value”
attribute=”value”………….] %>

The table given below describes the possible
attributes for the page directive.

Syntax
Attribute Description (default value is Example
in bold)
This tells the server about
the language to be used <%@ page
language in the JSP file. Presently language="java" language="java"
the only valid value for %>
this attribute is java.
This attribute defines the import="packag <%@ page
Import list of packages, each e.class" import="java.util.
separated by comma . *, java.io.*"%>
Indicates the superclass <%@ page
extends="packa
Extends of servlet when jsp extends="com.Co
ge.class"
translated in servlet. nnect"%>

true indicates session
should be bound to the
existing session if one
exists, otherwise a new session="true| <%@ page
Session
session should be created false" session="true"%>
and bound to it and false
indicates that no sessions
will be used.
specifies the buffer size buffer="sizekb| <%@ page
Buffer
for out and default is 8kb. none" buffer="8kb"%>
True indicates
multithreading and false <%@ page
isThreadSafe="tr
isThreadSafe indicates that the servlet isThreadSafe="tr
ue|false"
should implement ue"%>
SingleThreadModel

true indicates that the
buffer should be flushed
when it is full and false
autoflush="tru <%@ page
autoFlush indicates indicates that
e|false" autoFlush="true"%>
an exception should be
thrown when the buffer
overflows.
<%@ page
This defines a string that info="This is a simple
info="message
Info can be retrieved via the jsp file created by
"
getServletInfo method. Java2all team on 22
Feb 2011"%>
<%@ page
pageEncodin This defines data type of pageEncoding=
pageEncoding="ISO-
g page encoding. "ISO-8859-1"
8859-1"%>
contentType This specifies the MIME contentType=" <%@ page
type of the output. MIME-Type" contentType="text/h
tml;
charset=ISO-8859-1"

<%@ page
This defines isELIgnored="
isELIgnored isELIgnored="false
ENUM data type. true|false "
"%>

This indicates
whether or not <%@ page
isErrorPage="true
isErrorPage the current page isErrorPage="false
|false"
can act as the "%>
error page.
Define a URL to
another JSP that
is invoked if an <%@ page
errorPage unchecked errorPage="url" errorPage="error.j
runtime sp"%>
exception is
thrown.

<%@ page language="java"
import="java.util.*,java.io.*"
extends="com.Connect"
autoFlush="true"
errorPage="error.jsp"
info="This is a simple jsp file created by Java2all team on 22 Feb 2011"
isELIgnored="false"
isErrorPage="false"
session="true"
buffer="8kb"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"
isThreadSafe="true"
%>

NOTE :
The XML equivalent of

<%@ page import="java.util.*" %> is
<jsp:directive.page import="java.util.*" />

b) include directive :

It allows a JSP developer to include source code
(static resource) of a file inside jsp file at the
specified place at a translation time.

Typically include files are used for headers,
footers, tables and navigation that are common to
multiple pages.

The included page should not be another
dynamic page so the included file does not need to be
a complete and valid JSP or servlet.

Syntax:
<%@ include file="/folder_name/file_name"%>

If the included file and JSP file are available in
the same folder then the folder name is not required in
syntax.

<%@ include file="file_name"%>

Now we are describe the include directive by
one simple example so the use of include directive in
JSP file is easily understand.

Step-1 : Create two folder in webRoot
(i) HTMLFILE and (ii) JSPFILE.

Step-2 : Create a new HTML file(Included.html) in
HTMLFILE folder.

Step-3 : Replace the source code of a
file(Included.html) by the below code.
<html>
<head>
<title> Included.html </title>
</head>

<body>
This is HTML page which is include in JSP file by using directive include tag in JSP file. 
</body>
</html>

Step-4 : Create a jsp file(IncludeDemo.jsp) in
JSPFILE folder.
Step-5 : Now replace the source code of a
file(IncludeDemo.jsp) by the below code.
<%@ page language="java" import="java.util.*,java.io.*" pageEncoding="ISO-8859-1"%>
<html>
<head>

<title> IncludeDemo.jsp </title>
</head>

<body>
This is a JSP page. 
<%@ include file="/HTMLFILE/“Included.html"%>
</body>
</html>

Step-6 : Now Redeploy the Project and start the
Server.
Step-7 : Enter the appropriate URL in web-
browser.


Output :

This is a JSP page.
This is HTML page which is include in jsp file
by using directive include tag in jsp file.


c) taglib directive :

The taglib directive makes custom actions
available in current page through the use of tag
library.

Syntax:
<%@ taglib uri="tag Library_path"
prefix="tag_prefix"%>

uri ====> The absolute path (URL) of a Tag Library
Descriptor.
prefix ====> A unique prefix used to identify custom
tags from library used later in the JSP page. http://www.java2all.com

EX.

<%@ taglib uri="/tlds/TableGenerator.tld"
prefix="tg"%>

And if TableGenerator.tld defines a tag named
table, then the JSP file can contain tag of following
type:
<tg:table>
……….
……….
</tg:table>
NOTE : We discuss taglib directory in detail in
further chapter. http://www.java2all.com

JSP Standard Action elements


JSP Standard Action elements:

Actions are high-level JSP elements that create,
modify or use other objects.

Unlike directives and scripting elements, JSP are
coded using strict XML syntax form.

By the use of JSP actions elements you can
dynamically insert a file, reuse JavaBeans
components, forward the user to another page, or
generate HTML for the Java plugin etc.

The standard action types are:

(1) <jsp:param>
(2) <jsp:include>
(3) <jsp:forward>
(4) <jsp:fallback>
(5) <jsp:plugin>
(6) <jsp:useBean>
(7) <jsp:setProperty>
(8) <jsp:getProperty>

(1) <jsp:param>

The <jsp:param> action is used to provide other
tags with additional information in the form of name
value pairs.

This action is used in conjunction with
jsp:include, jsp:forward and jsp:plugin actions.

Syntax :
<jsp:param name=”parameter_name”
value=”parameter_value” />

OR
value=”parameter_value”>
</ jsp:param>

For Example,
<jsp:param name=”font_size” value=”20” />

OR

<jsp:param name=”font_size” value=”20”>
</jsp:param >

(2) <jsp:include>

This action allows a static or dynamic resource
to be including in the JSP at request time.

If page is buffered then the buffer is flushed
prior to the inclusion.

Syntax :

<jsp:include page= “file_name” flush = “true|false”
/>

OR
<jsp:include page= “file_name” flush = “true|false” >
</jsp:include >

NOTE :
A <jsp:include> action may have one or more
<jsp:param> tags in its body, to provide additional
name-value pairs.

Included.jsp :-
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<html>
<head>
<title>Included.jsp</title>
</head>
<body>
This is the message of Included.jsp file.............. 
</body>
</html>

Include.jsp :-
<html>
<head>
<title>Include.jsp</title>
</head>
<body>
This is the message of Include.jsp file.............. 
<jsp:include page="Included.jsp" />
</body>
</html>

Now run the Included.jsp in the appropriate
browser so you can get the below output in the
browser,

Output:
This is the message of Include.jsp file..............
This is the message of Included.jsp file..............

Example-2 :
Write a simple program which demonstrate the
use of <jsp:param> in <jsp:include> action element.

Employee.jsp :-

<html>
<head>
<title>Employee.jsp</title>
</head>
<body>
<% out.print("Name : "+request.getParameter("name1")); %> 
<% out.print("He is a "+request.getParameter("profile1")+" dept. in Noble Engineering College -
Junagadh."); %> 
<% out.print("Name : "+request.getParameter("name2"));%> 
<% out.print("He is a "+request.getParameter("profile2")+" dept. in Noble Engineering College -
Junagadh."); %>
</body>
</html>

Information.jsp :-

<html>
<head>
<title>Information.jsp</title>
</head>
<body>
<jsp:include page="Employee.jsp">

<jsp:param value="Prof. Ashutosh A. Abhangi" name="name1"/>
<jsp:param value="H.O.D. of Info. Tech. " name="profile1"/>

<jsp:param value="Prof. Kamal N. Kotecha" name="name2"/>
<jsp:param value="H.O.D. of C.S.E. " name="profile2"/>

</jsp:include>
</body>
</html>

Now run the Information.jsp in the appropriate
browser,

Output:
Name : Prof. Ashutosh A. Abhangi
He is a H.O.D. of Info. Tech. dept. in Noble
Engineering College - Junagadh.
Name : Prof. Kamal N. Kotecha
He is a H.O.D. of C.S.E. dept. in Noble Engineering
College - Junagadh.


NOTE : Difference between Directive include
and Action include element.

Included
Include Syntax Done when Parsing
Content

<%@include
file=”file_na Compilation
Directive Static Container
me”%> time

<jsp:include Request Not parsed
Static or
Action page=”file_n Processing but included
dynamic
ame”%> time in container

(3) <jsp:forward>
With the forward action, the current page stops
processing the request and forwards the request to
another page.
Execution never returns to the calling (current)
page.
Syntax :
<jsp:forward page= “file_name” />
OR
<jsp: forward page= “file_name”>
</jsp: forward> http://www.java2all.com

The meaning as well as use of the attributes and
the <jsp:param> element are same as for
<jsp:Include> action element.
Example-1 :
Write a simple program which demonstrate the
<jsp:forward> action element.
Current.jsp :
<html>
<head>
<title>Current.jsp</title>
</head>
<body>
This is a Current page
<jsp:forward page="Forward.jsp" />
</body>
</html>

Forward.jsp :
<html>
<head>
<title>Forward.jsp</title>
</head>
<body>
Welcome, Forward is working now and this is a Forwarded page............... 
</body>
</html>

Now run the Current.jsp in the appropriate
browser,
Output:
Welcome, Forward is working now and this is a
Forwarded page...............

Example-2 :
Write a simple Login Application by using
<jsp:forward> action element.
Login.jsp :
<html>
<head>
<title>Login.jsp</title>
</head>
<body>
<form action="Check.jsp">
User Name : <input type="text" name="name"> 
Password : <input type="text" name="password"> 
<input type="submit" value="Sign in">
<input type="reset" value="Reset">
</form>
</body>
</html>

Check.jsp :
<html>
<head>
<title>Check.jsp</title>
</head>
<body>
<%
String name = request.getParameter("name");
String password = request.getParameter("password");
if(name.equals("Ashutosh") && password.equals("java"))
{ %>
<jsp:forward page="Success.jsp"></jsp:forward>
<% }
else {
%>
<jsp:forward page="Retry.jsp"></jsp:forward>
<%
}
%>
</body>
</html>

Retry.jsp :
<html>
<head>
<title>Retry.jsp</title>
</head>
<body>
Wrong User ID and Password, Please try again by click below link………… 
<a href="Login.jsp"> Login page </a>
</body>
</html>

Success.jsp :
<html>
<head>
<title>Success.jsp</title>
</head>
<body>
<h1>You are successfully login................. </h1>
</body>
</html>

Now run the Login.jsp in the appropriate
browser so you can get the below output,


Now put the,
User Name : aaaaaa
Password : jjjjjj
And click on Sign in button so you can get the
below output in browser,
Output :
Wrong User ID and Password, Please try again
by click below link……………………..
Login page
By clicking the Login page link, the Login.jsp
page is call and you can put the


User Name : Ashutosh
Password : java
And click on Sign in button so you can get the
below output in browser,

Output :

You are successfully login.................


(4) <jsp:fallback>

Syntax :

<jsp:fallback> text message for user </jsp:fallback>

A text message to display for the user if the
plug-in cannot be started.
If the plug-in starts but the applet or Bean does
not, the plug-in usually displays a popup window
explaining the error to the user.
Its use with <jsp:plugin> element. http://www.java2all.com

(5) <jsp:plugin>

By the use of <jsp:plugin> you can include an
applet and JavaBean in your JSP page. Syntax of
<jsp:plugin> is :

Syntax :
<jsp:plugin type="bean|applet“
code="className.class“
codebase="Path of className.class
after moving it in WebRoot“
[ name="name of bean or applet instance" ]
[ align="bottom|top|middle|left|right" ]
[ height="displayPixels" ]
[ width="displayPixels" ]
[ jreversion=" version of Java Runtime
environment " ]
................. >

[<jsp:params>
<jsp:param name="parameter_name"
value="parameter_value" />
..........
</jsp:params>]
[<jsp:fallback>
text messag..........
</jsp:fallback>]
</jsp:plugin>

Example-1 :

Write a simple application in which the applet is
used in JSP file by <jsp:plugin> action element.

• Create a Applet_Jsp.java file(applet) in default
package at src in your Web Project(JSP_EXAMPLE).

The source code of this java file(applet) are as
under,

Applet_Jsp.java :
import java.applet.Applet;
import java.awt.Button;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Applet_Jsp extends Applet implements ActionListener
{
public void init()
{
setBackground(Color.black);
Button r = new Button("RED");
add(r);
r.addActionListener(this);
Button g = new Button("GREEN");
add(g);
g.addActionListener(this);
Button b = new Button("BLUE");
add(b);
b.addActionListener(this);
}

public void actionPerformed(ActionEvent e) {
if(e.getActionCommand().equals("RED"))
setBackground(Color.red);
if(e.getActionCommand().equals("BLUE"))
setBackground(Color.blue);
if(e.getActionCommand().equals("GREEN"))
setBackground(Color.green);

}
}

(2) Now, Run this applet.
(3) Create one new folder, name is AppletClass in
WebRoot.
(3) Now,Copy the Applet_Jsp.class file(compile
file/Bytecode file) which is available at……………
workspace.metadata.me_tcatwebappsYour_Project_na
meWEB-INFclasses Applet_Jsp.class in AppletClass folder
in WebRoot. http://www.java2all.com

(4) Create a Applet_Use_In_Jsp.jsp file in JSPFILES
folder at your Web Project(JSP_EXAMPLE).
The source code of this jsp file are as under,
Applet_Use_In_Jsp.jsp :
<%@ page language="java" %>
<html>
<head>
<title>Applet_Use_In_Jsp.jsp</title>
</head>
<body>
<jsp:plugin type="applet" code="Applet_Jsp.class" codebase="
http://localhost:8080/JSP_EXAMPLE/AppletClass"
width="500" height="500">
<jsp:fallback>
Unable to load Applet..............
</jsp:fallback>
</jsp:plugin>
</body>
</html> http://www.java2all.com

• <jsp:useBean>

Forms are a very common method of
interactions in web sites.The standard way of
handling forms in JSP is to define a "bean".

For that you just need to define a class that has
a field corresponding to each field in the form.
The class contains the "setters" and “getter”
method of the form fields.
By this action element <jsp:useBean>, we use
java bean in a JSP page.

Syntax :
<jsp:useBean id="bean id" class="bean's class"
scope="page|request|session| application" />

Scope of <jsp:useBean> :
1. page: This is default value. It means that we can
use the Bean within the JSP page.
It indicates that the bean is only available on the
current page (stored in the PageContext of the
current page).
2. request: It means that we can use the Bean from
any JSP page processing the same request.

A value of request indicates that the bean is only
available for the current client request (stored in
the ServletRequest object).
3. session: It means that we use the Bean from
any Jsp page in the same session as the JSP page
that created the Bean.
A value of session indicates that the object is
available to all pages during the life of the current
HttpSession.

4. application: It means that we use the Bean from
any page in the same application as the Jsp page
that created the Bean. http://www.java2all.com

A value of application indicates that it is
available to all pages that share the same
ServletContext.

(7) <jsp:setProperty>

This action sets the value of a bean’s property.
Syntax :

<jsp:setProperty name="bean's id"
property="property Name”value="property value"/
>

(8) <jsp:getProperty>

This element retrieves the value of a bean
property, converts it to a string, and inserts it into the
output.

Syntax :
<jsp:getProperty name="bean's id"
property="property name"/>

Example : Write a simple program which
demonstrate the <jsp:useBean>,<jsp:getProperty>
and <jsp:setProperty> action elements.

Student_Data.java :
package bean;
public class Student_Data
{
private String name = null;
private String email = null;
private int age = 0;

public String getName()
{
return name;
}
public String getEmail()
{
return email;
}
public int getAge()
{
return age;
}


public void setName(String name)
{
this.name = name;
}
public void setEmail(String email)
{
this.email = email;
}
public void setAge(int age)
{
this.age = age;
}
}


BeanData.jsp :
<html>
<head>
<title>BeanData.jsp</title>
</head>
<body>
<jsp:useBean id="student" class="bean.Student_Data" scope="page">
<jsp:setProperty name="student" property="name" value="Rahul"/>
<jsp:setProperty name="student" property="email" value="rahul.kumar@gmail.com"/>
<jsp:setProperty name="student" property="age" value="20"/>
</jsp:useBean>
<h1> STUDENT DATA : </h1>
 Name : <jsp:getProperty name="student" property="name"/> 
 Email-ID : <%= student.getEmail() %> 
 Age : <jsp:getProperty name="student" property="age"/> 
</body>
</html>

Now run the BeanData.jsp in the appropriate
browser,

Output :
STUDENT DATA :
Name : Rahul
Email-ID : rahul.kumar@gmail.com
Age : 20


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