为什么会报错Exception in thread "main" java.text.ParseException: Unparseable date: "2048-08-0912:12:12"？

package java_five;

import java.text.ParseException;
import java.util.Date;

public class DateDemo {
    public static void main(String [] args) throws ParseException {
        Date d=new Date();
        
        String s1=DateUtils.dateToString(d,"yyyy年MM月dd日 HH:mm:ss");
        System.out.println(s1);
         
        String s="2048-08-0912:12:12";
        Date dd=DateUtils.stringToDate(s, "yyyy-MM-ddHH:mm:ss");
        System.out.println(dd);
        //Date start = (Date)dateFm.parseObject(startTime);
    }

}