mysql+servlet+tomcat实现登陆注册代码

好的，以下是一份基本的MySQL + Servlet + Tomcat实现登录注册的代码示例，仅供参考：

1. 创建数据库和用户表：

CREATE DATABASE user_db;

USE user_db;

CREATE TABLE user (
  id INT(11) NOT NULL AUTO_INCREMENT,
  username VARCHAR(50) DEFAULT NULL,
  password VARCHAR(50) DEFAULT NULL,
  PRIMARY KEY (id)
);

2. 编写Servlet代码：

- 注册Servlet代码：

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class RegisterServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // 获取表单数据
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        // 连接数据库
        Connection con = null;
        PreparedStatement ps = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/user_db", "root", "password");

            // 判断用户名是否已存在
            ps = con.prepareStatement("SELECT * FROM user WHERE username = ?");
            ps.setString(1, username);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                response.sendRedirect("register.jsp?error=1");
                return;
            }

            // 插入用户数据
            ps = con.prepareStatement("INSERT INTO user (username, password) VALUES (?, ?)");
            ps.setString(1, username);
            ps.setString(2, password);
            ps.executeUpdate();

            // 注册成功，跳转到登录页面
            response.sendRedirect("login.jsp?success=1");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (ps != null) {
                    ps.close();
                }
                if (con != null) {
                    con.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

- 登录Servlet代码：

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // 获取表单数据
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        // 连接数据库
        Connection con = null;
        PreparedStatement ps = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/user_db", "root", "password");

            // 验证用户名和密码
            ps = con.prepareStatement("SELECT * FROM user WHERE username = ? AND password = ?");
            ps.setString(1, username);
            ps.setString(2, password);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                // 登录成功，跳转到主页
                response.sendRedirect("index.jsp");
            } else {
                response.sendRedirect("login.jsp?error=1");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (ps != null) {
                    ps.close();
                }
                if (con != null) {
                    con.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

3. 在Web页面中添加注册和登录表单：

- 注册表单：

<form method="post" action="RegisterServlet">
    <div>
        <label>用户名:</label>
        <input type="text" name="username" required>
    </div>
    <div>
        <label>密码:</label>
        <input type="password" name="password" required>
    </div>
    <div>
        <input type="submit" value="注册">
    </div>
</form>

- 登录表单：

<form method="post" action="LoginServlet">
    <div>
        <label>用户名:</label>
        <input type="text" name="username" required>
    </div>
    <div>
        <label>密码:</label>
        <input type="password" name="password" required>
    </div>
    <div>
        <input type="submit" value="登录">
    </div>
</form>

4. 在Web页面中添加JavaScript代码，实现表单验证和提交表单的功能。

以上代码仅为示例代码，需要根据实际情况进行修改和优化。