基于JSP实现一个简单计算器的方法

   /**
    * 两个数相减
    */
   public double subtract(double num1, double num2) {
       return num1 - num2;
   }

   /**
    * 两个数相乘
    */
   public double multiply(double num1, double num2) {
       return num1 * num2;
   }

   /**
    * 两个数相除
    */
   public double divide(double num1, double num2) {
       return num1 / num2;
   }

}
```

1. 编写CalculatorController类。

```java
package com.example.controller;

import com.example.model.Calculator;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CalculatorController {
private Calculator calculator;

   /**
    * 处理加法请求
    */
   public ModelAndView add(HttpServletRequest request, HttpServletResponse response) {
       double num1 = Double.parseDouble(request.getParameter("num1"));
       double num2 = Double.parseDouble(request.getParameter("num2"));

       double result = calculator.add(num1, num2);

       ModelAndView modelAndView = new ModelAndView();
       modelAndView.addObject("result", result);
       modelAndView.setViewName("result");
       return modelAndView;
   }

   /**
    * 处理减法请求
    */
   public ModelAndView subtract(HttpServletRequest request, HttpServletResponse response) {
       double num1 = Double.parseDouble(request.getParameter("num1"));
       double num2 = Double.parseDouble(request.getParameter("num2"));

       double result = calculator.subtract(num1, num2);

       ModelAndView modelAndView = new ModelAndView();
       modelAndView.addObject("result", result);
       modelAndView.setViewName("result");
       return modelAndView;
   }

   /**
    * 处理乘法请求
    */
   public ModelAndView multiply(HttpServletRequest request, HttpServletResponse response) {
       double num1 = Double.parseDouble(request.getParameter("num1"));
       double num2 = Double.parseDouble(request.getParameter("num2"));

       double result = calculator.multiply(num1, num2);

       ModelAndView modelAndView = new ModelAndView();
       modelAndView.addObject("result", result);
       modelAndView.setViewName("result");
       return modelAndView;
   }

   /**
    * 处理除法请求
    */
   public ModelAndView divide(HttpServletRequest request, HttpServletResponse response) {
       double num1 = Double.parseDouble(request.getParameter("num1"));
       double num2 = Double.parseDouble(request.getParameter("num2"));

       double result = calculator.divide(num1, num2);

       ModelAndView modelAndView = new ModelAndView();
       modelAndView.addObject("result", result);
       modelAndView.setViewName("result");
       return modelAndView;
   }

   public void setCalculator(Calculator calculator) {
       this.calculator = calculator;
   }

}
```

1. 编写JSP页面，实现计算器的UI界面。

```html
<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core"%>
<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%>