DateTimeFormatter desiredFormatter 
            = DateTimeFormatter.ofPattern("uuuu-MM-dd'T'HH:mm:ss.SSSSSS");
    String truncatedDateTimeString = "2017-06-05T19:27";
    LocalDateTime dateTime = LocalDateTime.parse(truncatedDateTimeString);
    String fixedDateTimeString = dateTime.format(desiredFormatter);
    System.out.println(fixedDateTimeString);

此打印

2017-06-05T19:27:00.000000

2017-06-05T19:27:00.000000

如果还缺少分钟和小时，那么我们还需要更多技巧.查看 DateTimeFormatterBuilder 及其 parseDefaulting 方法.在格式模式字符串中使用方括号 [] 包围可能缺少的部分.我不确定如果小时数被截断，您的字符串会是什么样子? T 也会丢失吗?

If also the minutes and hours are missing, we need some more trickery, though. Look into DateTimeFormatterBuilder and its parseDefaulting method. Use square brackets [] in the format pattern string to surround the parts that may be missing. I am not sure what your string will look like if the hours have been truncated — will the T be missing too?

另一方面，如果字符串为 2017-06-05T19:27:10.917360 ，上述方法同样适用，在这种情况下，只需将相同的字符串打印回去即可.

On the other hand the above also works if the string was 2017-06-05T19:27:10.917360, and in this case just prints the same string back.

我也不确定您真正要解决的问题.尾随零是多余的，那么将其截断是什么问题?

Also I am not sure which problem you are really trying to solve. Trailing zeroes are redundant, so what is the problem in them being truncated?

以下方法完善了我对 DateTimeFormatterBuilder ，其 parseDefaulting 方法和格式模式字符串中的方括号所说的内容:

The following method fleshes out what I said about DateTimeFormatterBuilder, its parseDefaulting method and square brackets in the format pattern string:

public static String addTrailingZerosToTimestamp(String timeStamp) {
    DateTimeFormatter truncatedFormatter = new DateTimeFormatterBuilder()
            .appendPattern("uuuu-MM-dd['T'HH[:mm[:ss[.SSSSSS]]]]")
            .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();
    DateTimeFormatter desiredFormatter 
            = DateTimeFormatter.ofPattern("uuuu-MM-dd'T'HH:mm:ss.SSSSSS");
    LocalDateTime dateTime = LocalDateTime.parse(timeStamp, truncatedFormatter);
    return dateTime.format(desiredFormatter);
}

它与 2017-06-05 ， 2017-06-05T19 ， 2017-06-05T19:27 ，2017-06-05T19:27:10 和 2017-06-05T19:27:10.917360 ，但不适用于 2017-06-05T19:27:10.917

It works with 2017-06-05, 2017-06-05T19, 2017-06-05T19:27, 2017-06-05T19:27:10 and 2017-06-05T19:27:10.917360, but not with 2017-06-05T19:27:10.917.