一個(gè)類想要成為javabean有以下幾個(gè)要求：
- 提供一個(gè)默認(rèn)的無參構(gòu)造函數(shù)。
- 需要被序列化并且實(shí)現(xiàn)了Serializable接口。
- 可能有一系列可讀寫屬性。
- 可能有一系列的"getter"或"setter"方法
public class User implements Serializable{
private String name;
private String password;
public User(){}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
javabean的引入：
<body>
<%--id：對(duì)象名
class：類
scope：該對(duì)象會(huì)存在的域
application session request page
--%>
<jsp:useBean id="user" class="com.xxjqr.JspStudy.date0901.User" scope="page">
</jsp:useBean>
</body>
原理：
javabean只是一個(gè)特殊的類，使用userBean標(biāo)簽引用bean其結(jié)果就是創(chuàng)建了一個(gè)bean對(duì)象；首先會(huì)通過對(duì)應(yīng)的域?qū)ο笕カ@取bean對(duì)象，如果bean對(duì)象為空，那么根據(jù)對(duì)應(yīng)的灰創(chuàng)建對(duì)應(yīng)的bean對(duì)象；
（打開翻譯后的java代碼可見）
user = (com.xxjqr.JspStudy.date0901.User) _jspx_page_context.getAttribute("user", javax.servlet.jsp.PageContext.PAGE_SCOPE);
if (user == null){
user = new com.xxjqr.JspStudy.date0901.User();
_jspx_page_context.setAttribute("user", user, javax.servlet.jsp.PageContext.PAGE_SCOPE);
out.write('\r');
out.write('\n');
out.write(' ');
}
注意：
Paste_Image.png
javabean的使用：
<body>
<jsp:useBean id="user" class="com.xxjqr.JspStudy.date0901.User"></jsp:useBean>
<%--
手動(dòng)設(shè)置屬性
<jsp:setProperty property="name" name="user" value="丁昌江"/>
--%>
<%--
1. 從參數(shù)中設(shè)置屬性
<jsp:setProperty property="name" name="user" param="name"/>
<jsp:setProperty property="password" name="user" param="password"/>
2. 從參數(shù)中設(shè)置屬性（javabean類中的參數(shù)名要和提交參數(shù)名一樣哦）
--%>
<jsp:setProperty property="*" name="user"/>
<%--獲取屬性
1. <%=user.getName() %>
2. name:${user.name } //el表達(dá)式和上面等價(jià)
--%>
name:<jsp:getProperty property="name" name="user"/><br/>
password:${user.password }
</body>
Paste_Image.png
Paste_Image.png
javabean練習(xí)之計(jì)算器：
Calc.jsp
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<link rel="stylesheet" >
<style type="text/css">
.myBody{
margin:0px auto;
padding: 10px;
width: 300px;
height: 500px;
}
</style>
</head>
<body class="myBody">
<jsp:useBean id="calc" class="com.xxjqr.JspStudy.d0902.Calc"></jsp:useBean>
<jsp:setProperty property="*" name="calc"/>
<%
calc.calculate();
%>
<form action="${pageContext.request.contextPath}/Calc/Calc.jsp" method="get">
<div class="form-group">
<label for="exampleInputEmail1">第一個(gè)值</label>
<input type="text" name="firstParam" value="" class="form-control" id="exampleInputEmail1" placeholder="">
</div>
<div class="form-group">
<label for="exampleInputPassword1">第二個(gè)值</label>
<input type="text" name="secondParam" value="" class="form-control" id="exampleInputPassword1" placeholder="">
</div>
<div class="form-group">
操作符
<select name="operator" class="form-control">
<option value='+'>+</option>
<option value='-'>-</option>
<option value='*'>*</option>
<option value='/'>/</option>
</select>
</div>
<button type="submit" class="btn btn-default">計(jì)算</button>
</form>
<hr/>
結(jié)果:${calc.result}
</body>
</html>
Calc.java
public class Calc implements Serializable{
private String firstParam = "0";
private String secondParam = "0";
private char operator = '+';
private String result = "0";
public Calc(){}
public String getFirstParam() {
return firstParam;
}
public void setFirstParam(String firstParam) {
this.firstParam = firstParam;
}
public String getSecondParam() {
return secondParam;
}
public void setSecondParam(String secondParam) {
this.secondParam = secondParam;
}
public char getOperator() {
return operator;
}
public void setOperator(char operator) {
this.operator = operator;
}
public String getResult() {
return result;
}
public void setResult(String result) {
this.result = result;
}
public String calculate(){
BigDecimal first=new BigDecimal(firstParam);
BigDecimal second=new BigDecimal(secondParam);
switch(operator){
case '+':
result = first.add(second).toString();
break;
case '-':
result = first.subtract(second).toString();
break;
case '*':
result = first.multiply(second).toString();
break;
case '/':
if (second == new BigDecimal(0))
result = "操作錯(cuò)誤";
result = first.divide(second).toString();
break;
}
return result;
}
}
calc.gif
