1、jsp开发模式：
1.sun公司推出jsp技术后，同时也推荐了两种web应用程序的开发模式，一种是JSP+JavaBean、一种是Servlet+jsp+javabean
2.jsp+javabean模式适合开发业务逻辑不太复杂的web应用程序，这种模式下，javabean用于封装业务数据，jsp则负责处理用户请求，又显示数据。
3.Servlet+jsp+javabean（MVC）模式适合开发复杂的web应用，在这种模式下，servlet负责处理用户请求，jsp负责数据显示，javabean模式程序
各个模块之间层次清晰，web开发推荐采用这种模式。
2、使用模式一编写计算器
使用jsp+javabean编写一个计算器（calculator）页面，javabean具有firstNum、secondNUm、result、operator属性，并提供一个calculate方法。
CalculatorBean.java
package cn.itcast.domain;
import java.math.BigDecimal;
//封装计算器数据的bean
public class CalculatorBean {
private String firstNum="0";
private char operator='+';
private String secondNum="0";
private String result;
public String getFirstNum() {
return firstNum;
}
public void setFirstNum(String firstNum) {
this.firstNum = firstNum;
}
public char getOperator() {
return operator;
}
public void setOperator(char operator) {
this.operator = operator;
}
public String getSecondNum() {
return secondNum;
}
public void setSecondNum(String secondNum) {
this.secondNum = secondNum;
}
public String getResult() {
return result;
}
public void setResult(String result) {
this.result = result;
}
public void calculate(){
BigDecimal first=new BigDecimal(this.firstNum);
BigDecimal second=new BigDecimal(this.secondNum);
switch(this.operator){
case '+':{
this.result=first.add(second).toString();
break;
}
case '-':{
this.result=first.subtract(second).toString();
break;
}
case '*':{
this.result=first.multiply(second).toString();
break;
}
case '/':{
if(second.doubleValue()==0){
throw new RuntimeException("被除数不能为0！");
}
this.result=first.divide(second,20,BigDecimal.ROUND_HALF_UP).toString();
break;
}
default:
throw new RuntimeException("运算符只能是 + - * / ");
}
}
}
calculatorBean.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>计算器演示页面</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body style="text-align:center;">
<jsp:useBean id="calculatorBean" class="cn.itcast.domain.CalculatorBean" />
<jsp:setProperty name="calculatorBean" property="*"/>
<%
try{
calculatorBean.calculate();
}catch(Exception e){
out.write(e.getMessage());
}
%>
<br />------------------------------------------------------------------<br />
计算结果是：
<jsp:getProperty name="calculatorBean" property="firstNum"/>
<jsp:getProperty name="calculatorBean" property="operator"/>
<jsp:getProperty name="calculatorBean" property="secondNum"/>
=
<jsp:getProperty name="calculatorBean" property="result"/>
<br />------------------------------------------------------------------<br />
<form action="/day09/calculator.jsp" method="post">
<table width="40%" border="1" bordercolor="red" align="center">
<tr>
<td colspan="2">简单的计算器</td>
</tr>
<tr>
<td>第一个参数</td>
<td>
<input type="text" name="firstNum">
</td>
</tr>
<tr>
<td>操作符</td>
<td>
<select name="operator">
<option value="+">+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
</td>
</tr>
<tr>
<td>第二个参数</td>
<td>
<input type="text" name="secondNum">
</td>
</tr>
<tr>
<td colspan="2">
<input type="submit" value="计算">
</td>
</tr>
</table>
</form>
</body>
</html>
效果图如上！