建立工具类，获取连接时只需调用类方法即可

工具类 

public class DBManager {
    public static final String DEFAULT_PWD = "123456";
    public static final String DEFAULT_UID = "root";
    public static final String DEFAULT_URL = "jdbc:mysql://localhost:3306/schoolforum?useSSL=false&serverTimezone=UTC";
    public static final String DEFAULT_DRIVER = "com.mysql.cj.jdbc.Driver";
 
    public static Connection getConn() {
        Connection con = null;
 
        try {
            Class.forName(DEFAULT_DRIVER); //加载驱动
            con = DriverManager.getConnection(DEFAULT_URL, DEFAULT_UID, DEFAULT_PWD); //获取连接
        } catch (ClassNotFoundException e) {
            System.out.println("数据库驱动加载失败");
            e.printStackTrace();
        } catch (SQLException e) {
            System.out.println("数据库连接失败");
            e.printStackTrace();
        }
 
        return con;
    }
 
}

调用方式

    //登录
    @SneakyThrows
    public User selectOneByUsernameAndPassword(String username,String password){
        String sql = "select uid, uName, uPwd, uImg, uSign, uTextNum from user where uName = ? and uPwd = ?";
        try (Connection c = DBManager.getConn()){
            System.out.println("connection success");
            try (PreparedStatement ps = c.prepareStatement(sql)){
                ps.setString(1,username);
                ps.setString(2,password);
 
                System.out.println("DEBUG: " + ps);
                try (ResultSet rs = ps.executeQuery()){
                    if(!rs.next()){
                        return null;
                    }
 
                    User user = new User();
                    user.setUid(rs.getInt("uid"));
                    user.setUserName(username);
                    user.setUserPwd(password);
                    user.setUserImg(rs.getString("uImg"));
                    user.setUserSign(rs.getString("uSign"));
                    user.setUserTextNum(rs.getInt("uTextNum"));
                    return user;
                }
            }
        }
    }