JSP - JavaBeans
A
JavaBean is a specially constructed Java class written in the Java and coded
according to the JavaBeans API specifications.
Following
are the unique characteristics that distinguish a JavaBean from other Java
classes:
·
It provides a default,
no-argument constructor.
·
It should be
serializable and implement the Serializable interface.
·
It may have a number of
properties which can be read or written.
·
It may have a number of
"getter" and "setter" methods for the properties.
JavaBeans Properties:
A
JavaBean property is a named attribute that can be accessed by the user of the
object. The attribute can be of any Java data type, including classes that you
define.
A
JavaBean property may be read, write, read only, or write only. JavaBean properties
are accessed through two methods in the JavaBean's implementation class:
|
Method
|
Description
|
|
getPropertyName()
|
For
example, if property name is firstName,
your method name would be getFirstName() to read that property. This method
is called accessor.
|
|
setPropertyName()
|
For
example, if property name is firstName,
your method name would be setFirstName() to write that property. This method
is called mutator.
|
A read-only attribute will have only a getPropertyName()
method, and a write-only attribute will have only a setPropertyName()
method.
Accessing JavaBeans:
The useBean action declares a JavaBean for use in
a JSP. Once declared, the bean becomes a scripting variable that can be
accessed by both scripting elements and other custom tags used in the JSP. The
full syntax for the useBean tag is as follows:
<jsp:useBean id="bean's name" scope="bean's scope" typeSpec/>
Here values for the scope attribute could be page, request,
session or application based on your requirement. The value of the id attribute may be any value as a long
as it is a unique name among other useBean declarations in the same JSP.
ccessing JavaBeans Properties:
Along
with <jsp:useBean...>, you can use <jsp:getProperty/> action to
access get methods and <jsp:setProperty/> action to access set methods.
Here is the full syntax:
<jsp:useBean id="id" class="bean's class" scope="bean's scope">
<jsp:setProperty name="bean's id" property="property name"
value="value"/>
<jsp:getProperty name="bean's id" property="property name"/>
...........
</jsp:useBean>
The
name attribute references the id of a JavaBean previously introduced to the JSP
by the useBean action. The property attribute is the name of the get or set
methods that should be invoked.
Following
is a simple example to access the data using above syntax:
<html>
<head>
<title>get and set properties Example</title>
</head>
<body>
<jsp:useBean id="students"
class="com.tutorialspoint.StudentsBean">
<jsp:setProperty name="students" property="firstName"
value="Zara"/>
<jsp:setProperty name="students" property="lastName"
value="Ali"/>
<jsp:setProperty name="students" property="age"
value="10"/>
</jsp:useBean>
<p>Student First Name:
<jsp:getProperty name="students" property="firstName"/>
</p>
<p>Student Last Name:
<jsp:getProperty name="students" property="lastName"/>
</p>
<p>Student Age:
<jsp:getProperty name="students" property="age"/>
</p>
</body>
</html>
Let
us make StudentsBean.class available in CLASSPATH and try to access above JSP.
This would produce following result:
Student First Name: Zara
Student Last Name: Ali
Student Age: 10
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