问题

我有这个字符串
> Fri, 07 Aug 2020 18:00:00 +0000

我需要将其转换为一个LocalDateTime

我尝试了几种方法：

创建一个DateTimeFormatter并解析字符串

String dateString = "Fri, 07 Aug 2020 18:00:00 +0000";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("E, dd MMM yyyy HH:mm:ss", Locale.getDefault());
LocalDateTime parsedDate = LocalDateTime.parse(dateString, formatter);

将其转换为Date并使用SimpleDateFormat，然后将resultDate转换为LocalDateTime

String dateString = "Fri, 07 Aug 2020 18:00:00 +0000";
SimpleDateFormat dateFormatter = new SimpleDateFormat("E, dd MMM yyyy HH:mm:ss Z");
Date date = dateFormatter.parse(dateString);
LocalDateTime localDateTime = date.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();

这两种方法都会给我同样的异常：

java.time.format.DateTimeParseException: Text 'Fri, 07 Aug 2020 18:00:00 +0000' could not be parsed 
at index 0 at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2046)

我该如何将该字符串转换？

String dateString = "Fri, 07 Aug 2020 18:00:00 +0000";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("E, dd MMM yyyy HH:mm:ss", Locale.getDefault());
LocalDateTime parsedDate = LocalDateTime.parse(publishedString, formatter);

String dateString = "Fri, 07 Aug 2020 18:00:00 +0000";
SimpleDateFormat dateFormatter = new SimpleDateFormat("E, dd MMM yyyy HH:mm:ss Z");
Date date = dateFormatter.parse(publishedString);
LocalDateTime localDateTime = date.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();

java.time.format.DateTimeParseException: Text 'Fri, 07 Aug 2020 18:00:00 +0000' could not be parsed 
at index 0 at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2046)

答案1

得分: 5

OffsetDateTime.parse( 
    "Fri, 07 Aug 2020 18:00:00 +0000" , 
    DateTimeFormatter.RFC_1123_DATE_TIME 
)

# `LocalDateTime` is the wrong class

Your input string contains `+0000` which indicates an offset-from-UTC. 

So you should not be using `LocalDateTime`. That class purposely lacks any concept of time zone or offset. With `LocalDateTime`, your string `Fri, 07 Aug 2020 18:00:00 +0000` will become 6M on August 7th 2020, but we won't know if that is 6 PM in Tokyo Japan, 6 PM in Toulouse France, or 6 PM in Toledo Ohio US — all different moments several hours apart.

# `OffsetDateTime`

Instead, this value should be parsed as [`OffsetDateTime`][2].

# Parsing

Your input's format is that of [RFC 1123][3]. That particular format is predefined in *java.time*. 

```java
String input = "Fri, 07 Aug 2020 18:00:00 +0000";
DateTimeFormatter f = DateTimeFormatter.RFC_1123_DATE_TIME;
OffsetDateTime odt = OffsetDateTime.parse( input , f );

odt.toString(): 2020-08-07T18:00Z

<details>
<summary>英文:</summary>

# tl;dr

    OffsetDateTime.parse( 
        &quot;Fri, 07 Aug 2020 18:00:00 +0000&quot; , 
        DateTimeFormatter.RFC_1123_DATE_TIME 
    )

See this [code run live at IdeOne.com][1].

# `LocalDateTime` is the wrong class

Your input string contains `+0000` which indicates an offset-from-UTC. 

So you should not be using `LocalDateTime`. That class purposely lacks any concept of time zone or offset. With `LocalDateTime`, your string `Fri, 07 Aug 2020 18:00:00 +0000` will become 6M on August 7th 2020, but we won&#39;t know if that is 6 PM in Tokyo Japan, 6 PM in Toulouse France, or 6 PM in Toledo Ohio US — all different moments several hours apart.

# `OffsetDateTime`

Instead, this value should be parsed as [`OffsetDateTime`][2].

# Parsing

Your input&#39;s format is that of [RFC 1123][3]. That particular format is predefined in *java.time*. 

```java
String input = &quot;Fri, 07 Aug 2020 18:00:00 +0000&quot;;
DateTimeFormatter f = DateTimeFormatter.RFC_1123_DATE_TIME;
OffsetDateTime odt = OffsetDateTime.parse( input , f );

>odt.toString(): 2020-08-07T18:00Z

答案2

得分: 4

我建议使用 Locale.ROOT，并不要忘记 DateTimeFormatter 类中的 Z。

String dateString = "Fri, 07 Aug 2020 18:00:00 +0000";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("E, dd MMM yyyy HH:mm:ss Z", Locale.ROOT);
LocalDateTime parsedDate = LocalDateTime.parse(dateString, formatter);

String dateString = "Fri, 07 Aug 2020 18:00:00 +0000";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("E, dd MMM yyyy HH:mm:ss Z", Locale.ROOT);
LocalDateTime parsedDate = LocalDateTime.parse(dateString, formatter);

答案3

得分: 3

我明白你需要一个LocalDateTime，用于处理一个API的需求，该API由于你无法控制的设计问题，正试图使用LocalDateTime来表示一个时间点。

如果外部合同规定了LocalDateTime应该以哪个时区或UTC偏移量来理解，那么LocalDateTime可以工作，至少对于99.977%的情况。然而，在某一天，如果某位同事程序员没有阅读合同，就会导致编程错误，这是我们无法在代码中解决的问题，只能通过良好的注释来减轻。

例如，如果合同规定使用UTC，那么我们需要确保将时间转换为UTC。我们需要从字符串中获取偏移量来进行转换。

ZoneOffset contractualOffset = ZoneOffset.UTC;
String stringWeveGot = "Fri, 07 Aug 2020 18:00:00 +0000";
LocalDateTime convertedDateTime = OffsetDateTime
        .parse(stringWeveGot, DateTimeFormatter.RFC_1123_DATE_TIME)
        .withOffsetSameInstant(contractualOffset)
        .toLocalDateTime();
System.out.println(convertedDateTime);

输出：

> 2020-08-07T18:00

如果字符串中的偏移量要求为0，您需要验证它是否为0，否则错误将不会被注意到，用户将会获得错误的结果。例如：

OffsetDateTime parsedOdt = OffsetDateTime
        .parse(stringWeveGot, DateTimeFormatter.RFC_1123_DATE_TIME);
if (!parsedOdt.getOffset().equals(contractualOffset)) {
    throw new IllegalStateException("Offset must be " + contractualOffset
            + ", was " + parsedOdt.getOffset());
}
LocalDateTime convertedDateTime = parsedOdt.toLocalDateTime();

如果合同提到某个时区，将其转换为该时区。我以澳大利亚维多利亚为例：

ZoneId contractualZone = ZoneId.of("Australia/Victoria");
String stringWeveGot = "Fri, 07 Aug 2020 18:00:00 +0000";
LocalDateTime convertedDateTime = OffsetDateTime
        .parse(stringWeveGot, DateTimeFormatter.RFC_1123_DATE_TIME)
        .atZoneSameInstant(contractualZone)
        .toLocalDateTime();
System.out.println(convertedDateTime);

输出：

> 2020-08-08T04:00

在发生时钟被倒转的时间异常情况下，例如夏令时（DST）结束时，您将得到一个模糊的结果。

关于你的代码出了什么问题？你的异常的原因在这里解释了：

• new SimpleDateFormat(“hh:mm a”, Locale.getDefault()).parse(“04:30 PM”) giving Unparseable exception
• java DateTimeFormatterBuilder fails on testtime

	ZoneOffset contractualOffset = ZoneOffset.UTC;
	String stringWeveGot = "Fri, 07 Aug 2020 18:00:00 +0000";
	LocalDateTime convertedDateTime = OffsetDateTime
			.parse(stringWeveGot, DateTimeFormatter.RFC_1123_DATE_TIME)
			.withOffsetSameInstant(contractualOffset)
			.toLocalDateTime();
	System.out.println(convertedDateTime);

    OffsetDateTime parsedOdt = OffsetDateTime
            .parse(stringWeveGot, DateTimeFormatter.RFC_1123_DATE_TIME);
    if (! parsedOdt.getOffset().equals(contractualOffset)) {
		throw new IllegalStateException("Offset must be " + contractualOffset
				+ ", was " + parsedOdt.getOffset());
	}
	LocalDateTime convertedDateTime = parsedOdt.toLocalDateTime();

	ZoneId contractualZone = ZoneId.of("Australia/Victoria");
	String stringWeveGot = "Fri, 07 Aug 2020 18:00:00 +0000";
	LocalDateTime convertedDateTime = OffsetDateTime
			.parse(stringWeveGot, DateTimeFormatter.RFC_1123_DATE_TIME)
			.atZoneSameInstant(contractualZone)
			.toLocalDateTime();
	System.out.println(convertedDateTime);