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Java Web 實作：將 JSP 註冊頁面資料寫入 MySQL 資料庫完整教學

編輯：程式設計疑難解答

前言

在開發 Java Web 應用程式時，使用者註冊功能是最基礎也最重要的模組之一。本文將完整示範如何從 JSP 註冊頁面接收使用者輸入的資料，透過 Servlet 處理業務邏輯，最後使用 JDBC 將資料安全地寫入 MySQL 資料庫的用戶表中。

完整實作流程

1. 建立資料庫與用戶表

首先在 MySQL 中建立資料庫與對應的用戶表：

CREATE DATABASE IF NOT EXISTS user_db CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
USE user_db;

CREATE TABLE IF NOT EXISTS users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL UNIQUE,
    password VARCHAR(255) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

2. 設計 JSP 註冊頁面 (register.jsp)

建立一個簡單的 HTML 表單，採用 POST 方法提交至 Servlet：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html>
<head>
    <title>使用者註冊</title>
    <meta charset="UTF-8">
</head>
<body>
    <h2>使用者註冊</h2>
    <form action="RegisterServlet" method="post">
        <div>
            <label>使用者名稱：</label>
            <input type="text" name="username" required>
        </div>
        <div>
            <label>電子郵件：</label>
            <input type="email" name="email" required>
        </div>
        <div>
            <label>密碼：</label>
            <input type="password" name="password" required>
        </div>
        <div>
            <label>確認密碼：</label>
            <input type="password" name="confirmPassword" required>
        </div>
        <button type="submit">註冊</button>
    </form>
</body>
</html>

3. 建立資料庫連線工具類 (DBUtil.java)

封裝資料庫連線邏輯，方便複用並統一管理連線參數：

package com.example.util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DBUtil {
    private static final String URL = "jdbc:mysql://localhost:3306/user_db?useSSL=false&serverTimezone=UTC&characterEncoding=UTF-8";
    private static final String USER = "root";
    private static final String PASSWORD = "your_password";

    static {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            throw new ExceptionInInitializerError("MySQL 驅動載入失敗: " + e.getMessage());
        }
    }

    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(URL, USER, PASSWORD);
    }

    public static void close(AutoCloseable... resources) {
        for (AutoCloseable res : resources) {
            if (res != null) {
                try {
                    res.close();
                } catch (Exception ignored) {}
            }
        }
    }
}

4. 實作註冊 Servlet (RegisterServlet.java)

核心業務邏輯：接收參數、驗證資料、密碼加密、預處理語句防止 SQL 注入、事務處理：

package com.example.servlet;

import com.example.util.DBUtil;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.*;
import java.io.IOException;
import java.sql.*;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

@WebServlet("/RegisterServlet")
public class RegisterServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=UTF-8");

        String username = req.getParameter("username").trim();
        String email = req.getParameter("email").trim();
        String password = req.getParameter("password");
        String confirmPassword = req.getParameter("confirmPassword");

        // 基本驗證
        if (username.isEmpty() || email.isEmpty() || password.isEmpty()) {
            req.setAttribute("error", "所有欄位皆為必填");
            req.getRequestDispatcher("/register.jsp").forward(req, resp);
            return;
        }

        if (!password.equals(confirmPassword)) {
            req.setAttribute("error", "兩次輸入密碼不一致");
            req.getRequestDispatcher("/register.jsp").forward(req, resp);
            return;
        }

        // 密碼加密 (SHA-256 + Salt 更佳，此處示範基本雜湊)
        String hashedPassword = hashPassword(password);

        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;

        try {
            conn = DBUtil.getConnection();
            conn.setAutoCommit(false); // 開啟事務

            // 檢查使用者名稱或郵箱是否已存在
            String checkSql = "SELECT id FROM users WHERE username = ? OR email = ?";
            pstmt = conn.prepareStatement(checkSql);
            pstmt.setString(1, username);
            pstmt.setString(2, email);
            rs = pstmt.executeQuery();

            if (rs.next()) {
                req.setAttribute("error", "使用者名稱或電子郵件已被註冊");
                req.getRequestDispatcher("/register.jsp").forward(req, resp);
                return;
            }

            // 插入新用戶
            String insertSql = "INSERT INTO users (username, password, email) VALUES (?, ?, ?)";
            pstmt = conn.prepareStatement(insertSql, Statement.RETURN_GENERATED_KEYS);
            pstmt.setString(1, username);
            pstmt.setString(2, hashedPassword);
            pstmt.setString(3, email);

            int affectedRows = pstmt.executeUpdate();
            if (affectedRows > 0) {
                conn.commit();
                req.setAttribute("success", "註冊成功！請登入");
            } else {
                conn.rollback();
                req.setAttribute("error", "註冊失敗，請稍後再試");
            }

        } catch (SQLException e) {
            try { if (conn != null) conn.rollback(); } catch (SQLException ignored) {}
            e.printStackTrace();
            req.setAttribute("error", "系統錯誤: " + e.getMessage());
            req.getRequestDispatcher("/register.jsp").forward(req, resp);
        } finally {
            DBUtil.close(rs, pstmt, conn);
        }

        req.getRequestDispatcher("/register.jsp").forward(req, resp);
    }

    private String hashPassword(String password) {
        try {
            MessageDigest md = MessageDigest.getInstance("SHA-256");
            byte[] hash = md.digest(password.getBytes());
            StringBuilder hex = new StringBuilder();
            for (byte b : hash) {
                hex.append(String.format("%02x", b));
            }
            return hex.toString();
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException("密碼加密失敗", e);
        }
    }
}