使用jdbc进行简单的增删改查

JDBC工具类

public class JDBCUtils {
    public static Connection getConnection(){
        Connection conn =null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/exam?characterEncoding=utf-8&useSSL=false&serverTimezone=UTC","root","123456");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }catch (SQLException e1){
            e1.printStackTrace();
        }
        return conn;
    }
}

Dao层代码

public class UserDaoImpl implements UserDao {
    public static Connection conn=JDBCUtils.getConnection();
    public static PreparedStatement preStatement;
    public static ResultSet set;
    /**
     * 查找所有用户的方法
     * @return
     */
    @Override
    public List<User> findAll() {
        List<User> list = new ArrayList<>();
        try {
            String sql = "select * from user";
            preStatement = conn.prepareStatement(sql);
            set = preStatement.executeQuery();
            while(set.next()){
                User user = new User();
                user.setId(set.getInt("id"));
                user.setUsername(set.getString("username"));
                user.setPassword(set.getString("password"));
                list.add(user);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return list;
    }

    /**
     * 删除用户方法
     * @param id
     * @return
     */
    @Override
    public int delete(int id) {
        try {
            String sql = "delete from user where id = ?";
            preStatement = conn.prepareStatement(sql);
            preStatement.setInt(1,id);
            return preStatement.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return 0;
    }

    /**
     * 更新用户方法
     * @param user
     * @return
     */
    @Override
    public int update(User user) {
        try {
            String sql = "update user set username=?,password=? where id = ?";
            preStatement = conn.prepareStatement(sql);
            preStatement.setString(1,user.getUsername());
            preStatement.setString(2,user.getPassword());
            preStatement.setInt(3,user.getId());
            return preStatement.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return 0;
    }

    /**
     * 保存用户方法
     * @param user
     * @return
     */
    @Override
    public int save(User user) {
        try {
            String sql = "insert into user(id,username,password) values(?,?,?)";
            preStatement = conn.prepareStatement(sql);
            preStatement.setInt(1,user.getId());
            preStatement.setString(2,user.getUsername());
            preStatement.setString(3,user.getPassword());
            return preStatement.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return 0;
    }

    /**
     * 单查询方法
     * @param id
     * @return
     */
    @Override
    public User findById(int id) {
        try {
            String sql = "select * from user where id  = ?";
            preStatement = conn.prepareStatement(sql);
            preStatement.setInt(1,id);
            set = preStatement.executeQuery();
            while(set.next()) {
                User user = new User();
                user.setId(set.getInt("id"));
                user.setUsername(set.getString("username"));
                user.setPassword(set.getString("password"));
                return user;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }
}