1.引入fastjson-1.2.43.jar 包到lib下面，下载地址链接: https://pan.baidu.com/s/1EgAOikoG4VJRJrnUw83SNA  密码: n2fr

import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.JSONObject;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.io.PrintWriter;import java.text.DecimalFormat;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;@WebServlet("/Servlet")public class CalculateServlet extends HttpServlet {    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doGet(request, response);    }    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        response.setContentType("text/json;charset=utf-8");        String numA = request.getParameter("numA");        String numB = request.getParameter("numB");        Float fnumA = Float.parseFloat(numA);        Float fnumB = Float.parseFloat(numB);        Float sum, minus, multiply, divide;        sum = fnumA + fnumB;        minus = fnumA - fnumB;        multiply = fnumA * fnumB;        divide = fnumA / fnumB;        DecimalFormat df = new DecimalFormat("#0.00");//取小数点后两位四舍五入        String sminus = df.format(minus);        String ssum = df.format(sum);        String smultiply = df.format(multiply);        String sdivide = df.format(divide);        Map
     
       map = new HashMap
      
       ();        map.put("sum",ssum);        map.put("minus",sminus);        map.put("multiply",smultiply);        map.put("divide",sdivide);        JSONObject json = JSONObject.parseObject(JSON.toJSONString(map));//把map转为json数据      PrintWriter out = response.getWriter();        out.write(json.toString());        out.flush();        out.close();            }}
      
     

　　前端jsp代码入下

<%--  Created by IntelliJ IDEA.  User: Administrator  Date: 2017/12/18  Time: 14:59  To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %>        
     
      
      numA:
      
      
      
      numB:
      
      
      
      
     
和为:
差为:
积为:
商为:

　　*注意如果出错，请将fastjson-1.2.43.jar复制一份到tomcat 的lib 目录下，然后重启项目。