Javaee登录注册数据库代码

以下是使用 JavaEE 技术实现登录注册功能的示例代码，使用 MySQL 数据库进行存储和查询。

### 数据库配置

首先需要创建一个名为 `user` 的数据库，并创建一个名为 `users` 的表，表结构如下：

CREATE TABLE `users` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(50) NOT NULL,
  `password` varchar(50) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

### 注册功能

package com.example;

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/register")
public class RegisterServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        
        if (username == null || username.trim().length() == 0) {
            request.setAttribute("message", "请输入用户名！");
            request.getRequestDispatcher("/register.jsp").forward(request, response);
            return;
        }
        
        if (password == null || password.trim().length() == 0) {
            request.setAttribute("message", "请输入密码！");
            request.getRequestDispatcher("/register.jsp").forward(request, response);
            return;
        }
        
        try {
            // 加载数据库驱动
            Class.forName("com.mysql.jdbc.Driver");
            
            // 获取数据库连接
            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/user", "root", "123456");
            
            // 查询是否已存在该用户
            String sql = "SELECT * FROM users WHERE username=?";
            PreparedStatement ps = conn.prepareStatement(sql);
            ps.setString(1, username);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                request.setAttribute("message", "该用户名已被注册！");
                request.getRequestDispatcher("/register.jsp").forward(request, response);
                return;
            }
            
            // 插入新用户
            sql = "INSERT INTO users (username, password) VALUES (?, ?)";
            ps = conn.prepareStatement(sql);
            ps.setString(1, username);
            ps.setString(2, password);
            ps.executeUpdate();
            
            request.setAttribute("message", "注册成功！");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
            request.setAttribute("message", "注册失败！");
            request.getRequestDispatcher("/register.jsp").forward(request, response);
        }
    }

}

### 登录功能

package com.example;

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

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;

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        
        try {
            // 加载数据库驱动
            Class.forName("com.mysql.jdbc.Driver");
            
            // 获取数据库连接
            Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/user", "root", "123456");
            
            // 查询用户是否存在
            String sql = "SELECT * FROM users WHERE username=? AND password=?";
            PreparedStatement ps = conn.prepareStatement(sql);
            ps.setString(1, username);
            ps.setString(2, password);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                // 登录成功，将用户信息存入 Session
                HttpSession session = request.getSession();
                session.setAttribute("username", username);
                response.sendRedirect(request.getContextPath() + "/main.jsp");
            } else {
                request.setAttribute("message", "用户名或密码错误！");
                request.getRequestDispatcher("/login.jsp").forward(request, response);
            }
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
            request.setAttribute("message", "登录失败！");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
        }
    }

}

以上示例代码仅供参考，实际开发中还需考虑数据加密、安全性等问题。