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
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);
}
}
测试登录界面
验证码错误
用户名密码错误
登录成功
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