Unknown character set index for field '255' received from server.

我的mysql是8.0.33 但是我jar也换了最新的不对，人去吃饭马上回来求答疑

public Connection getCon()
    {
        try
        {
            try
            {
                Class.forName("com.mysql.cj.jdbc.Driver");
            } catch (ClassNotFoundException e)
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            con = DriverManager.getConnection(url, user, password);
        } catch (SQLException e)
        {
            System.out.println("�������ݿ�����ʧ�ܣ�");
            con = null;
            e.printStackTrace();
        }
        return con;
    }
  url = "jdbc:mysql://localhost:3306/demo?useUnicode=true&characterEncoding=utf8"; url是在另一个类中直接复制过来的

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你的mysql的驱动包版本是多少？这个一般是你的mysql驱动jar包的版本太低导致的。