javaweb登录界面验证码自动生成，点击重新生成验证码，验证码与输入框的校验

ManagerLoginServlet类

String checkCode = req.getParameter("checkCode");

        //先校验验证码，只有验证码正确时，才校验登录的账号和密码
        //首先获取session,再获取session中的code属性的值，与输入框的值进行比较
        if (req.getSession().getAttribute("code").equals(checkCode)){
//验证码正确时，执行登录名和登录密码的验证
 }else {
            //验证码错误
            req.setAttribute("tips","登录失败，验证码错误！");
            req.getRequestDispatcher("login.jsp").forward(req,resp);
        }

下面是完整类中的代码

login.jsp界面（注意此时已经导入过jquery包了）

<%--
  Created by IntelliJ IDEA.
  User: lijianglin
  Date: 2022/5/19
  Time: 17:32
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>



    
    
    
    
    
    
    
    
    
    




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<%--    从ManagerLoginServlet类中获取过来提示信息，取属性的value--%>
                            提示 ${tips}
                        
                    

                    
                
            
        
    

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CheckCodeServlet类

package com.it.servlets;

import javax.imageio.ImageIO;
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 javax.servlet.http.HttpSession;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

@WebServlet("/CheckCodeServlet")
public class CheckCodeServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//通过java中awt中提供的类绘制验证码图片
//        1.创建一张图片
        int height=90;//验证码高度
        int width=300;//验证码宽度
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);//实例化一个图片对象
//        2.绘制图片对象，从图片对象中获取绘制图片的笔
        Graphics2D pen = image.createGraphics();
        //a.绘制背景
        pen.setColor(getRandomColor());
        pen.fillRect(0,0,width,height);//绘制实心矩形

        //b.绘制验证码字符串
        int letterNum=4;//验证码图片上的字符的个数
        int space=20;//验证码图片上两个字母之间的空隙
        int letterWidth=(width-(letterNum+1)*space)/letterNum;//计算每个字母占据的宽度

//        for循环每循环一次，绘制一个字母（小写字母的ascii码：97-122）
        Random random = new Random();
        String code ="";
        for (int i=0;i

package com.it.servlets;

import com.it.entity.Manager;
import com.it.service.ManagerService;

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.sql.SQLException;

//用于管理员登录验证的servlet
@WebServlet("/ManagerLoginServlet")
public class ManagerLoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// doGet中写了doPost方法，可以所有方法都在doPost方法，这样不管传过来是get还是post都可以成功调用方法
        doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//      1.接收账号、密码、验证码
        req.setCharacterEncoding("utf-8");
//        从输入框中获取输入的内容，参数是输入框的名字。
        String loginName = req.getParameter("loginName");
        String loginPwd = req.getParameter("loginPwd");
        String checkCode = req.getParameter("checkCode");

        //先校验验证码，只有验证码正确时，才校验登录的账号和密码
        //首先获取session,再获取session中的code属性的值，与输入框的值进行比较
        if (req.getSession().getAttribute("code").equals(checkCode)){
//验证码正确时，执行登录名和登录密码的验证
//      2.调用ManagerService进行校验
            ManagerService managerService = new ManagerService();
            try {
                Manager manager = managerService.checkManagerLogin(loginName, loginPwd);
//            3.判断验证结果
                if (manager==null){
//                登录失败，跳转到登录界面并进行错误提示
                    req.setAttribute("tips","登录失败，密码或账号错误！");
                    req.getRequestDispatcher("login.jsp").forward(req,resp);
                }else {
//                登录成功，跳转到index.jsp界面
                    resp.sendRedirect("index.jsp");
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }else {
            //验证码错误
            req.setAttribute("tips","登录失败，验证码错误！");
            req.getRequestDispatcher("login.jsp").forward(req,resp);
        }


    }
}