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.
JavaBeans Example:
Consider a student class with few properties:
package com.tutorialspoint;
public class StudentsBean implements java.io.Serializable
{
private String firstName = null;
private String lastName = null;
private int age = 0;
public StudentsBean() {
}
public String getFirstName(){
return firstName;
}
public String getLastName(){
return lastName;
}
public int getAge(){
return age;
}
public void setFirstName(String firstName){
this.firstName = firstName;
}
public void setLastName(String lastName){
this.lastName = lastName;
}
public void setAge(Integer age){
this.age = age;
}
}
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.
Following example shows its simple usage:
<html>
<head>
<title>useBean Example</title>
</head>
<body>
<jsp:useBean id="date" class="java.util.Date" />
<p>The date/time is <%= date %>
</body>
</html>
This would produce following result:
The date/time is Thu Sep 30 11:18:11 GST 2010
Accessing 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
