DateTimeFormatter 得到 LocalDateTime.withYear(0) 的令人困惑的结果？

Question

Java版本：

1.8.0_202

请参阅下面的代码：

DateTimeFormatter yy = DateTimeFormatter.ofPattern("yy");
DateTimeFormatter yyy = new DateTimeFormatterBuilder()
                .appendValueReduced(ChronoField.YEAR, 3, 3, 0)
                .toFormatter();
DateTimeFormatter yyyy = DateTimeFormatter.ofPattern("yyyy");

LocalDateTime now = LocalDateTime.now();
// set year is 0
LocalDateTime year0 = now.withYear(0);
System.out.println("year0: " + year0);                             // year0: 0000-01-10T09:53:03.551
System.out.println("year0.getYear(): \t" + year0.getYear());       // year0.getYear():    0
System.out.println("year0.format(yyyy): " + year0.format(yyyy));   // year0.format(yyyy): 0001
System.out.println("year0.format(yyy): \t" + year0.format(yyy));   // year0.format(yyy):  000
System.out.println("year0.format(yy): \t" + year0.format(yy));     // year0.format(yy):   01
System.out.println("============================================================");
// set year is 1
LocalDateTime year1 = now.withYear(1);
System.out.println("year1: " + year1);                             // year1: 0001-01-10T09:53:03.551
System.out.println("year1.getYear(): \t" + year1.getYear());       // year1.getYear():     1
System.out.println("year1.format(yyyy): " + year1.format(yyyy));   // year1.format(yyyy):  0001
System.out.println("year1.format(yyy): \t" + year1.format(yyy));   // year1.format(yyy):   001
System.out.println("year1.format(yy): \t" + year1.format(yy));     // year1.format(yy):    01

为什么

year0.format(yyyy)

和

year0.format(yy)

返回错误结果

0001

或

01

，而

year0.format(yyy)

返回正确结果

000

？如何修复？

Answer 1

不知道为什么“yyy”会给你一个不一致的结果，但是DateTimeFormatter的文档说

y

代表“纪元年份”，这意味着永远不应该给出0，因为没有纪元（AD或BC）有年份0. 根据这些相同的文档，如果您希望显示没有纪元的年份，则需要查找

u

而不是

y

。

如果要同时显示纪元和年份，那就是

G

，即

yyyy GG