错误类型：: Text '20201217' could not be parsed: Unable to obtain LocalDateTime from TemporalAccessor: {},ISO resolved to 2020-12-17 of type
String time = "20201217";
DateTimeFormatter dateFormat = ("yyyyMMdd");
LocalDateTime date = (time, dateFormat);
代码中，定义的time为yyyyMMdd, 在DateTimeFormatter时的格式是yyyyMMdd，这类错误是LocalDateTime类要求必须有yyyyMMddHHmmss格式，把LocalDateTime换为LocalDate，错误解决
总结： LocalDateTime其实是 LocalDate + LocalTime 两部分都得有，不然会报错