实现了UserDao

src/backend/dao/impl/UserDao.java

@@ -0,0 +1,137 @@
+package backend.dao.impl;
+
+import backend.dao.interfaces.UserDaoIF;
+import backend.model.User;
+import backend.utils.DBHelper;
+
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.List;
+
+public class UserDao implements UserDaoIF {
+
+    @Override
+    public User findByUsername(String username) {
+        User user = null;
+        //1. 从连接池中创建数据库连接
+        Connection conn = DBHelper.getInstance().getConnection();
+        //2. 创建Statement对象
+        String sql = "select username,password,role,email,createdAt from USER where username = ?";
+        try {
+            PreparedStatement stmt = conn.prepareStatement(sql);
+            stmt.setString(1, username);
+            ResultSet rs = stmt.executeQuery();
+            while (rs.next()) {
+                user = new User();
+                user.setUsername(rs.getString("username"));
+                user.setPassword(rs.getString("password"));
+                user.setRole(rs.getString("role"));
+                user.setEmail(rs.getString("email"));
+                user.setCreatedAt(rs.getTimestamp("createdAt"));
+            }
+        } catch (SQLException e) {
+            System.out.println("查询用户失败: " + e.getMessage());
+        }
+        return user;
+    }
+    @Override
+    public User findById(int id) {
+        User user = null;
+        //1. 从连接池中创建数据库连接
+        Connection conn = DBHelper.getInstance().getConnection();
+        //2. 创建Statement对象
+        String sql = "select username,password,role,email,createdAt from USER where id = ?";
+        try{
+            PreparedStatement stmt = conn.prepareStatement(sql);
+            stmt.setInt(1,id);
+            ResultSet rs = stmt.executeQuery();
+            while(rs.next()) {
+                user = new User();
+                user.setUsername(rs.getString("username"));
+                user.setPassword(rs.getString("password"));
+                user.setRole(rs.getString("role"));
+                user.setEmail(rs.getString("email"));
+                user.setCreatedAt(rs.getTimestamp("createdAt"));
+            }
+        }catch (SQLException e) {
+            System.out.println("查询用户失败: " + e.getMessage());
+        }
+        return user;
+    }
+
+    @Override
+    public boolean addUser(User user) {
+        Connection conn = DBHelper.getInstance().getConnection();
+        String sql = "insert into USER (username,password,role,email,createdAt) values (?,?,?,?,?)";
+        try{
+            PreparedStatement stmt = conn.prepareStatement(sql);
+            stmt.setString(1,user.getUsername());
+            stmt.setString(2,user.getPassword());
+            stmt.setString(3,user.getRole());
+            stmt.setString(4,user.getEmail());
+            stmt.setTimestamp(5,user.getCreatedAt());
+            return stmt.executeUpdate() > 0;
+        } catch (SQLException e) {
+            System.out.println("添加用户失败: " + e.getMessage());
+        }
+        return false;
+    }
+
+    @Override
+    public boolean updateUser(User user) {
+        Connection conn = DBHelper.getInstance().getConnection();
+        String sql = "update USER set username = ?,password = ?,role = ?,email = ?,createdAt = ? where id = ?";
+        try{
+            PreparedStatement stmt = conn.prepareStatement(sql);
+            stmt.setString(1,user.getUsername());
+            stmt.setString(2,user.getPassword());
+            stmt.setString(3,user.getRole());
+            stmt.setString(4,user.getEmail());
+            stmt.setTimestamp(5,user.getCreatedAt());
+            stmt.setInt(6,user.getId());
+            return stmt.executeUpdate() > 0;
+        } catch (SQLException e) {
+            System.out.println("更新用户失败: " + e.getMessage());
+        }
+        return false;
+    }
+
+    @Override
+    public boolean deleteUser(int id) {
+        Connection conn = DBHelper.getInstance().getConnection();
+        String sql = "delete from USER where id = ?";
+        try{
+            PreparedStatement stmt = conn.prepareStatement(sql);
+            stmt.setInt(1,id);
+            return stmt.executeUpdate() > 0;
+        } catch (SQLException e) {
+            System.out.println("删除用户失败: " + e.getMessage());
+        }
+        return false;
+    }
+
+    @Override
+    public List<User> findAll() {
+        Connection conn = DBHelper.getInstance().getConnection();
+        String sql = "select id,username,password,role,email,createdAt from USER";
+        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.setRole(rs.getString("role"));
+                user.setEmail(rs.getString("email"));
+                user.setCreatedAt(rs.getTimestamp("createdAt"));
+                return List.of(user);
+            }
+        }catch (SQLException e) {
+            System.out.println("查询所有用户失败: " + e.getMessage());
+        }
+        return List.of();
+    }
+}

src/backend/dao/interfaces/UserDaoIF.java

@@ -7,7 +7,7 @@ import java.util.*;
  * 用户数据访问接口
  * 定义了用户相关的数据库操作方法
  */
-public interface UserDao {
+public interface UserDaoIF {
     /**
      * 根据用户名查找用户
      * @param username 用户名