如何在Java 8(Scala)中将日期时间字符串转换为long(UNIX Epoch Time) [英] How to convert a date time string to long (UNIX Epoch Time) in Java 8 (Scala)

问题描述

我想要一些pattern中的字符串的UNIX纪元时间(Posix Time，Unix Time)，该字符串采用常规格式(即UTC).请使用Java 8，而不是Joda或旧Java.

I want the UNIX Epoch Time (Posix Time, Unix Time) of a string in some pattern, the string is in normal format (so UTC). Please using Java 8, not Joda or old Java.

(毫秒，请参见

(For milliseconds please see How to convert a date time string to long (UNIX Epoch Time) Milliseconds in Java 8 (Scala))

到目前为止，我有以下内容，但出于多种原因，我对此很讨厌:

So far I have the below, but I hate this for a number of reasons:

1. 对于日期最常见的事情(转换为UNIX Epoch Time)，它太冗长了. 7种方法要求应为1.
2. 它必须指定UTC，但可以肯定的是，UTC只是一个默认值，为什么我必须在此处明确说明?
3. 它具有字符串文字"UTC"
4. 它有一个魔术数字ZoneOffset.ofHours(0)

1. It's way too verbose for what is the most common thing to do with dates (convert to UNIX Epoch Time). 7 method calls for what should be 1.
2. It has to specify UTC, but surely UTC is just a default, why do I have to be explicit here?
3. It has a string literal "UTC"
4. It has a magic number ZoneOffset.ofHours(0)

到目前为止，我最好的:

My best so far:

def dateTimeStringToEpoch(s: String, pattern: String): Long = 
    LocalDateTime.parse(s, DateTimeFormatter.ofPattern(pattern))
      .atZone(ZoneId.ofOffset("UTC", ZoneOffset.ofHours(0)))
      .toInstant().getEpochSeconds

还有，奖金问题，效率高吗?通过DateTimeFormatter.ofPattern(pattern)创建DateTimeFormatter是否有任何开销?如果可以，为什么?

Also, bonus question, is it efficient? Is there any overhead to creating the DateTimeFormatter via DateTimeFormatter.ofPattern(pattern)? If so why?

推荐答案

此解决方案要短两倍以上(仅3个方法调用):

This one is more than two times shorter (only 3 method calls):

def dateTimeStringToEpoch(s: String, pattern: String): Long = 
     LocalDateTime.parse(s, DateTimeFormatter.ofPattern(pattern))
                  .toEpochSecond(ZoneOffset.UTC)

顺便说一句，我将在dateTimeStringToEpoch之外构建DateTimeFormatter并将其作为方法参数传递:

Btw, I would build the DateTimeFormatter outside of dateTimeStringToEpoch and pass it as a method parameter:

def dateTimeStringToEpoch(s: String, formatter: DateTimeFormatter): Long = 
     LocalDateTime.parse(s, formatter).toEpochSecond(ZoneOffset.UTC)

实际上已经进行了性能测试，所以在方法之外初始化DateTimeFormatter的性能几乎没有差异(几乎是2倍).

Having actually run a performance test, there is little difference in performance (barely a factor of 2) in initialising the DateTimeFormatter outside the method.

scala> val pattern = "yyyy/MM/dd HH:mm:ss"
pattern: String = yyyy/MM/dd HH:mm:ss

scala>   time(() => randomDates.map(dateTimeStringToEpoch(_, pattern)))
Took: 1216

scala>   time(() => randomDates.map(dateTimeStringToEpochFixed))
Took: 732

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