Copyright © tutorialspoint.com
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.
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.
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; } } |
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 |
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 |
Copyright © tutorialspoint.com