书店管理系统的Java后台代码

书店管理系统的Java后台代码可以分为不同的模块，例如用户管理、商品管理、订单管理等。下面是一个简单的用户管理模块的代码示例：

// User.java
public class User {
    private int id;
    private String username;
    private String password;
    private String email;

    // 构造函数、getter、setter等省略
}

// UserDao.java
public class UserDao {
    // 连接数据库等操作省略

    // 查询所有用户
    public List<User> findAll() throws SQLException {
        List<User> users = new ArrayList<>();
        String sql = "SELECT * FROM users";
        try (PreparedStatement stmt = conn.prepareStatement(sql);
             ResultSet rs = stmt.executeQuery()) {
            while (rs.next()) {
                User user = new User();
                user.setId(rs.getInt("id"));
                user.setUsername(rs.getString("username"));
                user.setPassword(rs.getString("password"));
                user.setEmail(rs.getString("email"));
                users.add(user);
            }
        }
        return users;
    }

    // 添加用户
    public void add(User user) throws SQLException {
        String sql = "INSERT INTO users (username, password, email) VALUES (?, ?, ?)";
        try (PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setString(1, user.getUsername());
            stmt.setString(2, user.getPassword());
            stmt.setString(3, user.getEmail());
            stmt.executeUpdate();
        }
    }

    // 更新用户
    public void update(User user) throws SQLException {
        String sql = "UPDATE users SET username=?, password=?, email=? WHERE id=?";
        try (PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setString(1, user.getUsername());
            stmt.setString(2, user.getPassword());
            stmt.setString(3, user.getEmail());
            stmt.setInt(4, user.getId());
            stmt.executeUpdate();
        }
    }

    // 删除用户
    public void delete(int id) throws SQLException {
        String sql = "DELETE FROM users WHERE id=?";
        try (PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setInt(1, id);
            stmt.executeUpdate();
        }
    }
}

// UserController.java
public class UserController {
    private UserDao userDao = new UserDao();

    // 查询所有用户
    public void findAll(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<User> users = userDao.findAll();
        request.setAttribute("users", users);
        request.getRequestDispatcher("/user/list.jsp").forward(request, response);
    }

    // 添加用户
    public void add(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        User user = new User();
        user.setUsername(request.getParameter("username"));
        user.setPassword(request.getParameter("password"));
        user.setEmail(request.getParameter("email"));
        userDao.add(user);
        response.sendRedirect(request.getContextPath() + "/user");
    }

    // 更新用户
    public void update(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        User user = new User();
        user.setId(Integer.parseInt(request.getParameter("id")));
        user.setUsername(request.getParameter("username"));
        user.setPassword(request.getParameter("password"));
        user.setEmail(request.getParameter("email"));
        userDao.update(user);
        response.sendRedirect(request.getContextPath() + "/user");
    }

    // 删除用户
    public void delete(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        userDao.delete(id);
        response.sendRedirect(request.getContextPath() + "/user");
    }
}

以上代码仅供参考，实际项目中需要根据具体需求进行修改和完善。同时需要注意的是，书店管理系统一般还需要考虑安全性、性能等方面的问题。