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JSP JavaBeans

来源:ZzWww 编辑:ZzWww 时间:2019-07-27

JSP - JavaBeans

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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 −

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 the 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 −

S.No. Method & Description

1

getPropertyName()

For example, if property name is firstName, your method name would be getFirstName() to read that property. This method is called accessor.

2

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 can be a 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 how to use the useBean action −

<html> <head> <title>useBean Example</title> </head> <body> <jsp:useBean id = "date" class = "java.util.Date" /> <p>The date/time is <%= date %> </body> </html>

You will receive the following result − −

The date/time is Thu Sep 30 11:18:11 GST 2010 Accessing JavaBeans Properties

Along with <jsp:useBean...> action, you can use the <jsp:getProperty/> action to access the get methods and the <jsp:setProperty/> action to access the 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 the set methods that should be invoked.

Following example shows how to access the data using the 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 the StudentsBean.class available in CLASSPATH. Access the above JSP. the following result will be displayed −

Student First Name: Zara Student Last Name: Ali Student Age: 10

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