使用 Java 8 转换像 Joda DateTime(String) 这样的日期时间字符串 [英] Convert date time string like Joda DateTime(String) with Java 8

问题描述

我有一个 API，它可以以三种可能的格式返回 JSON 中的日期值:

I have an API that can return date values in JSON in three possible formats:

1. 2017-04-30T00:00+02:00
2. 2016-12-05T04:00
3. 2016-12-05

我需要将所有三个转换为 java.time.LocalTimeDate.Joda 在 DateTime 对象上有一个很好的构造函数，它接受所有三种格式作为字符串并转换它们.DateTime dt = new DateTime(StringFromAPI); 就够了.

I need to convert all three into a java.time.LocalTimeDate. Joda has a nice constructor on the DateTime object which takes in all three formats as Strings and converts them. DateTime dt = new DateTime(StringFromAPI); is enough.

Java 8(java.time 包)中是否有类似的功能?看来我现在首先必须对 String 进行正则表达式来检查格式，然后创建一个 LocalDateTime、ZonedDateTime 或 LocalDate 并将后者 2. 转换为 LocalDateTime.对我来说似乎有点麻烦.有没有简单的方法?

Is there a similar capability in Java 8 (java.time package)? It seems I now first have to regex the String to check the format, then create either a LocalDateTime, ZonedDateTime or LocalDate and convert the latter 2. to LocalDateTime. Seems a bit cumbersome to me. Is there a easy way?

推荐答案

我提出了两个选项，每个选项都有其优缺点.

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

一，构建自定义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，有人很容易发现它有点棘手.对于您问题中的三个示例字符串，它会生成:

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

另一种选择，依次尝试三种不同的格式，然后选择一种有效的格式:

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，还是有人认为它比第一个选项更直接?我认为仅依赖内置的 ISO 格式是有好处的.三个示例字符串的结果与上述相同.

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.

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