java.time 如何解析各种模式的日期时间格式(具有所有可选时间组件，除了年份)

我需要将表示DateTime的字符串解析为要操作的Java 8 DateTime对象.例如，有效字符串为(ALL datetime components (except year) are optional):

2015
2015-01
2015-01-01
2015-02-03T00
2015-02-03T00:30
2015-02-03T00:30:50
2015-02-03T00:30:50Z
2015-02-03T00:30:50.333Z
2015-02-03T00:30:50.333+03:00
2015-02-03T00:30:50.333+0300
2015-02-03T00:30:50.333-08
2015-02-03T00:30:50.333GMT+8
2015-02-03GMT+8
2015-02UTC-3
2015-02PST
...

我从https://stackoverflow.com/a/52823661/2028440找到的最好的代码(包括我从https://stackoverflow.com/a/65985789/2028440开始的调整)，

                DateTimeFormatter dtf = new DateTimeFormatterBuilder()
                .appendValue(ChronoField.YEAR, 4)
                .appendPattern("[['-']MM[['-']dd[['T']HH[[':']mm[[':']ss['.'SSS]]]]]][Z][O][VV]")
                .parseDefaulting(ChronoField.MONTH_OF_YEAR, 1)
                .parseDefaulting(ChronoField.DAY_OF_MONTH, 1)
                .parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
                .parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0)
                .parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0)
                .parseDefaulting(ChronoField.NANO_OF_SECOND, 0)
                .toFormatter();

        String[] s = {
                "2018",
                "2018-10",
                "2018-10-15",
                "2018-10-15T12:00",
                "2018-10-15T12:00:30",
                "2018-10-15T12:00:30.123Z",
                "2018-10-15T12:00:30.123-0800",
                "2018-10-15T12:00:30.123UTC-08:00",
                "2018-10-15T12:00:30.123GMT+9"
        };
        for (String line : s) {
            System.out.println(LocalDateTime.parse(line, dtf));
        }

控制台输出为:

2018-01-01T00:00
2018-10-01T00:00
2018-10-15T00:00
2018-10-15T12:00
2018-10-15T12:00:30
2018-10-15T12:00:30.123
2018-10-15T12:00:30.123
2018-10-15T12:00:30.123
2018-10-15T12:00:30.123

但是它不能正确地将时间偏移量解析为它打印的最后三个值2018-10-15T12:00:30.123.

他们每个人也应该得到print the correct time offset英镑. 以下是最后3个测试字符串的正确输出:

"2018-10-15T12:00:30.123-08:00"
"2018-10-15T12:00:30.123-08:00"
"2018-10-15T12:00:30.123+09:00"

它类似于以下命令的输出:

System.out.println(ZonedDateTime.parse("2018-10-15T12:00:30.123-08:00").toString());

prints

2018-10-15T12:00:30.123-08:00

当我试图改变的时候:

            System.out.println(LocalDateTime.parse(line, dtf));

致:

            System.out.println(ZonedDateTime.parse(line, dtf));

我收到了这样的错误:

Exception in thread "main" java.time.format.DateTimeParseException: Text '2018' could not be parsed: Unable to obtain ZonedDateTime from TemporalAccessor: {},ISO resolved to 2018-01-01T00:00 of type java.time.format.Parsed
    at java.base/java.time.format.DateTimeFormatter.createError(DateTimeFormatter.java:2017)
    at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1952)
    at java.base/java.time.ZonedDateTime.parse(ZonedDateTime.java:598)