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Session--验证码案例（Java）

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案例

用户输入用户名，密码以及验证码。

如果用户名和密码输入有误，跳转登录页面，提示:用户名或密码错误
如果验证码输入有误，跳转登录页面，提示：验证码错误
如果全部输入正确，则跳转到主页success.jsp，显示：用户名,欢迎您

思路

在生成验证码的时候将它的值存入到session中，在比对的时候再取出来进行对比

代码

index.jsp

<%--
  Created by IntelliJ IDEA.
  User: tanglei
  Date: 2020/6/26
  Time: 下午12:48
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>login</title>


    <script>
        window.onload = function(){
            document.getElementById("img").onclick = function(){
                this.src="/login_time_war_exploded/checkCode?time="+new Date().getTime();
            }
        }


    </script>
    <style>
        div{
            color: red;
        }

    </style>
</head>
<body>

<form action="/login_time_war_exploded/login" method="post">
    <table>
        <tr>
            <td>用户名</td>
            <td><input type="text" name="username"></td>
        </tr>
        <tr>
            <td>密码</td>
            <td><input type="password" name="password"></td>
        </tr>
        <tr>
            <td>验证码</td>
            <td><input type="text" name="checkCode"></td>
        </tr>
        <tr>
            <td colspan="2"><img id="img" src="/login_time_war_exploded/checkCode"></td>
        </tr>
        <tr>
            <td colspan="2"><input type="submit" value="登录"></td>
        </tr>
    </table>


</form>


<div><%=request.getAttribute("cc_error") == null ? "" : request.getAttribute("cc_error")%></div>
<div><%=request.getAttribute("login_error") == null ? "" : request.getAttribute("login_error") %></div>

</body>
</html>

success.jsp

<%--
  Created by IntelliJ IDEA.
  User: tanglei
  Date: 2020/6/26
  Time: 下午6:27
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1><%=request.getSession().getAttribute("user")%>,欢迎您</h1>
</body>
</html>

验证码checkCode.java

package cn.guizimo.servlet;

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 java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

@WebServlet("/checkCode")
public class CheckCode extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        int width = 100;
        int height = 50;
        //创建图片对象
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);

        //美化
        Graphics g = image.getGraphics();
        //背景
        g.setColor(Color.PINK);
        g.fillRect(0, 0, width, height);
        //边框
        g.setColor(Color.BLUE);
        g.drawRect(0, 0, width - 1, height - 1);

        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        Random ran = new Random();
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i <= 4; i++) {
            int index = ran.nextInt(str.length());
            char ch = str.charAt(index);
            sb.append(ch);
            g.drawString(ch+"",width/5*i,height/2);
        }
        String checkCode_session = sb.toString();
        //将验证码存入session
        req.getSession().setAttribute("checkCode_session",checkCode_session);

        //干扰线
        g.setColor(Color.GREEN);
        for (int i = 0; i < 10; i++) {
            int x1 = ran.nextInt(width);
            int x2= ran.nextInt(width);
            int y1 = ran.nextInt(height);
            int y2 = ran.nextInt(height);
            g.drawLine(x1,y1,x2,y2);
        }


   //输出图片到浏览器
        ImageIO.write(image, "jpg", resp.getOutputStream());

    }

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

login.java

package cn.guizimo.servlet;

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.io.IOException;

@WebServlet("/login")
public class Login extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.设置request编码
        req.setCharacterEncoding("utf-8");
        //2.获取参数
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String checkCode = req.getParameter("checkCode");
        //3.先获取生成的验证码
        HttpSession session = req.getSession();
        String checkCode_session = (String) session.getAttribute("checkCode_session");
        //删除session中存储的验证码
        //session.removeAttribute("checkCode_session");
        //3.先判断验证码是否正确
        if(checkCode_session!= null && checkCode_session.equalsIgnoreCase(checkCode)){
            //忽略大小写比较
            //验证码正确
            //判断用户名和密码是否一致
            if("zhangsan".equals(username) && "123".equals(password)){//需要调用UserDao查询数据库
                //登录成功
                //存储信息，用户信息
                session.setAttribute("user",username);
                //重定向到success.jsp
                resp.sendRedirect(req.getContextPath()+"/success.jsp");
            }else{
                //登录失败
                //存储提示信息到request
                req.setAttribute("login_error","用户名或密码错误");
                //转发到登录页面
                req.getRequestDispatcher("/login.jsp").forward(req,resp);
            }


        }else{
            //验证码不一致
            //存储提示信息到request
            req.setAttribute("cc_error","验证码错误");
            //转发到登录页面
            req.getRequestDispatcher("/login.jsp").forward(req,resp);

        }
    }

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