Ajax局部刷新原理—原生模式

1.原理 

 2.使用步骤

 附：readyState的5个属性值和status的3个属性值

3.演示示例，计算bmi（身体质量指数）

项目结构

前端页面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

  
        
        
  
  
      
        姓名

        身高米

        体重千克

        

        
      
  

请求映射

    
        BmiServlet
        com.bjpowernode.controller.AjaxServlet
    
    
        BmiServlet
        /bmiAjax
    

服务器处理，AjaxServlet

package com.bjpowernode.controller;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class AjaxServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String weight = request.getParameter("weight");
        String height = request.getParameter("height");

        Float h = Float.valueOf(height);
        Float w = Float.valueOf(weight);
        float bmi = w / (h * h);
        String msg = "";
        if (bmi <= 18.5) {
            msg = "偏瘦！";
        } else if (bmi > 18.5 && bmi <= 23.9) {
            msg = "正常！";
        } else if (bmi > 24 && bmi <= 27) {
            msg = "偏胖！";
        } else {
            msg = "肥胖！！";
        }
        String ms="你好，"+name+"先生/女士，你的bmi为"+bmi+"，你的身体状况为"+msg+"";
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out=response.getWriter();
        out.print(ms);
        out.flush();
        out.close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}