方立勋_30天掌握JavaWeb_(JSP+JavaBean实现)简单计算器

落日映苍穹つ 2022-06-18 10:25 60阅读 0赞

> 1.  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即负责处理用户请求，又显示数据。
> 2.  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负责封装数据。 Servlet+JSP、JavaBean模式程序各个模块之间层次清晰，web开发推荐采用此种模式。

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![这里写图片描述][SouthEast]

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。

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**JSP页面**

<%@ 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>
    <title>简单计算器</title>
    </head>
    
    <body style="text-align: center;">
    
        <jsp:useBean id="calculatorBean" class="com.java.domain.CalculatorBean"></jsp:useBean>
        <jsp:setProperty property="*" name="calculatorBean" />
        <% try{ calculatorBean.calculator(); }catch(Exception e){ out.write(e.getMessage()); } %>
        <br />-------------------------------------------------------------------------------
        <br> 计算结果是：
        <jsp:getProperty property="firstNum" name="calculatorBean" />
        <jsp:getProperty property="operator" name="calculatorBean" />
        <jsp:getProperty property="secondNum" name="calculatorBean" />
        =
        <jsp:getProperty property="result" name="calculatorBean" />
        <br />-------------------------------------------------------------------------------
        <br>
    
        <form action="/day09_calculator/calculator.jsp" method="post">
            <table width="50%" border="1px">
                <tr>
                    <td colspan="2">简单的计算器</td>
                </tr>
                <tr>
                    <td>第一个参数：</td>
                    <td><input name="firstNum" type="text"></td>
                </tr>
                <tr>
                    <td>运算符：</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 name="secondNum" type="text"></td>
                </tr>
                <tr>
                    <td colspan="2"><input type="submit" value="计算"></td>
                </tr>
            </table>
        </form>
    </body>
    </html>

**JavaBean**

package com.java.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 calculator() {
            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("被除数只能为+-*/");
            }
        }
    }

[SouthEast]: /images/20220618/2a1018d6d66e4ba4823c2b5399e667e4.png