我提出了两种选择，每种选择都有其优缺点。

I am presenting two options, each with its pros and cons.

一个，建立自定义 DateTimeFormatter 以接受您的三种可能的格式：

One, build a custom DateTimeFormatter to accept your three possible formats:

public static LocalDateTime parse(String dateFromJson) {
    DateTimeFormatter format = new DateTimeFormatterBuilder().append(DateTimeFormatter.ISO_LOCAL_DATE)
            .optionalStart()
            .appendLiteral('T')
            .append(DateTimeFormatter.ISO_LOCAL_TIME)
            .optionalStart()
            .appendOffsetId()
            .optionalEnd()
            .optionalEnd()
            .parseDefaulting(ChronoField.HOUR_OF_DAY, 0)
            .toFormatter();
    return LocalDateTime.parse(dateFromJson, format);
}

一方面，它很干净，另一方面，有人可以轻松找到它有点棘手。对于问题中的三个示例字符串，它会产生：

On one hand, it’s clean, on the other, someone could easily find it a bit tricky. For the three sample strings in your question it produces:

2017-04-30T00:00
2016-12-05T04:00
2016-12-05T00:00

另一个选择，尝试三个依次选择不同的格式：

The other option, try the three different formats in turn and pick the one that works:

public static LocalDateTime parse(String dateFromJson) {
    try {
        return LocalDateTime.parse(dateFromJson);
    } catch (DateTimeParseException e) {
        // ignore, try next format
    }
    try {
        return LocalDateTime.parse(dateFromJson, DateTimeFormatter.ISO_OFFSET_DATE_TIME);
    } catch (DateTimeParseException e) {
        // ignore, try next format
    }
    return LocalDate.parse(dateFromJson).atStartOfDay();
}

我不认为这是最漂亮的代码，仍然有人认为它是比第一种选择更直接？我认为仅依靠内置的ISO格式就可以保证质量。您的三个示例字符串的结果与上面相同。

I don’t consider this the most beautiful code, still some may think it’s more straightforward than the first option? I think there’s a quality in relying on the built-in ISO formats alone. The results for your three sample strings are the same as above.