After using JavaBean in JSP, we can realize the separation of HTML code and Java code, it is easier for JSP to develop and maintain. So JavaBean became a necessary tool for JSP programmers.
Although JavaBean is a Java class, it also has some of its own features
(1) JavaBean is a public class
(2) JavaBean has a construction method with no parameters
(3) The properties in JavaBean are manipulated by the get and set methods
For example: Define a circlearea of the JavaBean used to encapsulate the circle area of the calculation logic, after all the use of the circle area of the calculation method can be used to complete the javabean, the implementation of code reuse.
Circlearea.java
Package javabeantest;
public class Circlearea {
Define two properties (r: RADIUS; unit: Units)
Private double r=0;
Private String unit= "";
Non-parametric construction method
Public Circlearea () {
Super ();
}
Public double Getr () {
return R;
}
public void Setr (double r) {
THIS.R = R;
}
Public String Getunit () {
return unit;
}
public void Setunit (String unit) {
This.unit = unit;
}
Calculates the area of a circle and returns the calculated result
Public String Getarea () {
return 3.14*r*r+ "Square" +unit;
}
}
Use JavaBean in the JSP.
<%@ page language= "java" import= "java.util.*" pageencoding= "Utf-8"%>
<!--use JavaBean in JSP generally follow the following four steps
(1) class for importing JavaBean
(2) Instantiate a JavaBean object within the specified range, and if the object already exists, direct reference
(3) operation of the JavaBean instance object
(4) Removal of JavaBean from the specified range
-
<%@ page language= "java" import= "java.util.*" pageencoding= "Utf-8"%>
<% @pageimport= "Javabeantest.circlearea"%>
<jsp:usebean id= "Circle1" class= "Javabeantest.circlearea" scope= "page"/>
<jsp:usebean id= "Circle2" class= "Javabeantest.circlearea" scope= "Request"/>
<jsp:usebean id= "Circle3" class= "Javabeantest.circlearea" scope= "Session"/>
<jsp:usebean id= "circle4" class= "Javabeantest.circlearea" scope= "Application"/>
The application of <title>javabean in JSP </title>
<body>
<%
Invoke the JavaBean in the page range
CIRCLE1.SETR (4);
Circle1.setunit ("M");
Out.println (Circle1.getarea ());
Out.println ("<br/><br/>");
Call the JavaBean within the request scope
CIRCLE1.SETR (6);
Circle1.setunit ("M");
Out.println (Circle1.getarea ());
Out.println ("<br/><br/>");
Call the JavaBean within the session range
CIRCLE1.SETR (8);
Circle1.setunit ("M");
Out.println (Circle1.getarea ());
Out.println ("<br/><br/>");
Call the JavaBean in the application range
CIRCLE1.SETR (9);
Circle1.setunit ("M");
Out.println (Circle1.getarea ());
Out.println ("<br/><br/>");
%>
<%
Remove the Circle1 from the page range
Pagecontext.removeattribute ("Circle1");
Remove the circle2 from the request scope
Request.removeattribute ("Circle2");
Remove the Circle3 from the session range
Session.removeattribute ("Circle1");
Remove Circle4 from the application range
Application.removeattribute ("Circle1");
%>
</body>
A simple example of using JavaBean in JSP
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