JavaWeb简单的验证码登入

前端login.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<span>欢迎登录XXX管理系统</span>
<form action='./loginControler' method='post'>
    登录名称：
    <input type='text' name='Name' value='' /><br>
    登录密码：<input type='password' name='nPwd' value='' /><br>
    验证码：<input type='text' name='loginCode' value='' />
    <img src='./captcha' width=80 height=30/>
    <input type='submit' value='提交' /></form>
</body>
</html>

后端

LoginController.java

package cn.edu.mju.project2.comtroller;
import cn.edu.mju.project2.Util.StrUtil;
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;

@WebServlet("/loginControler")
public class LoginController extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String Name = req.getParameter("Name");
        String Pwd = req.getParameter("Pwd");
        String loginCode = req.getParameter("loginCode");
        String msg = null;

        String Code = (String) req.getSession().getAttribute("Code");

        if(StrUtil.isBank(loginCode)){
            msg = "请输入验证码";

        }else if (loginCode.equals(Code)){
            if("admin".equals(Name) && "admin".equals(Pwd)) {
                msg = "<font size='20'>hello " + Name + "</font>";
            }else{
                msg = "<font size='20'>账号或密码错误！</font>";
            }

        }else  {
            msg = "验证码错误
";
        }
        showMsg(resp, msg);
    }

    private void showMsg(HttpServletResponse resp, String msg){
        resp.setCharacterEncoding("utf-8");
        try{
            PrintWriter out = resp.getWriter();
            out.println("<html>");
            out.println("<header>");
            out.println("<title>test</title>");
            out.println("<meta charset="utf-8">");
            out.println("</header");
            out.println("<body>");
            out.println(msg);
            out.println("</body>");
            out.println("</html>");
            out.close();
        }catch (Exception ex){
            System.out.println(ex.getMessage());
        }

    }
}

CaptcheController.java

package cn.edu.mju.project2.comtroller;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

@WebServlet("/captcha")
public class CaptcheController extends HttpServlet {
    private final int WIDTH = 130;
    private final int HEIGHT = 50;
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        resp.setDateHeader("Expires", 0);
        resp.setHeader("Cache-Control", "no-cache");
        resp.setHeader("Pragma", "no-cache");


        BufferedImage img = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
        Graphics g = img.getGraphics();
        g.setColor(Color.white);
        g.fillRect(0,0, WIDTH, HEIGHT);

        String Code = getRandomString(4);

        req.getSession().setAttribute("Code",Code);

        g.setFont(new Font("宋体",Font.BOLD,30));
        g.setColor(Color.RED);
        g.drawString(Code,30,35);

        g.dispose();

        ServletOutputStream out = resp.getOutputStream();
        ImageIO.write(img, "PNG", out);
        try {
            out.flush();
        }catch (Exception ignored){}
        finally {
            out.close();
        }

}

    //length用户要求产生字符串的长度
    public static String getRandomString(int length){
        String str="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random=new Random();
        StringBuffer sb=new StringBuffer();
        for(int i=0;i<length;i++){
            int number=random.nextInt(62);
            sb.append(str.charAt(number));
        }
        return sb.toString();
    }


}

StrUtil.java

package cn.edu.mju.project2.Util;

public class StrUtil {
    public static boolean isBank(String src){
        if(src == null || src.equals("")){
            return true;
        }else {
            return false;
        }
    }

}

效果：

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原文地址：https://www.cnblogs.com/hlikex/p/12653227.html