更改Java时间戳格式会导致更改时间戳 [英] Changing Java Timestamp format causes a change of the timestamp

问题描述

我对Java时间戳格式化函数感到有些困惑，因为它们似乎将时间戳更改了几分钟。

I'm a bit puzzled regarding the Java timestamp formatting functions as they seem to change the timestamp by a few minutes.

我的Pivotal CloudFoundry应用程序写了一个新条目进入PostgreSQL 9.4.5数据库。这样做，我让PostgreSQL生成并存储该条目的时间戳（在SQL语句中，我对该特定列使用'now（）'）。
到目前为止一切正常。当我用我的应用程序读取条目时出现问题，因为我必须将时间戳格式化为ISO 8601（公司策略），这似乎改变了时间戳。我已经使用了这段代码：

My Pivotal CloudFoundry app writes a new entry into a PostgreSQL 9.4.5 database. Doing so, I let PostgreSQL generate and store a timestamp for that entry (within the SQL statement I use 'now()' for that particular column). All that works fine so far. Problems arise when I read the entry with my app because I have to format the timestamp to ISO 8601 (company policy) and this seems to change the timestamp. I've used this code:

public String parseTimestamp(String oldDate) {
    System.out.println("String oldDate: " + oldDate);

    TimeZone timeZone = TimeZone.getTimeZone("Europe/Berlin");
    SimpleDateFormat oldDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSSSS");
    SimpleDateFormat newDateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
    newDateFormat.setTimeZone(timeZone);

    Date tempDate = null;
    try {
        tempDate = oldDateFormat.parse(oldDate);
    } catch (ParseException e) {
        //TODO
    }

    System.out.println("tempDate before format(): " + tempDate);
    String newDate = newDateFormat.format(tempDate);
    System.out.println("tempDate after format(): " + tempDate);
    System.out.println("String newDate: " + newDate);
    return newDate;
}

输出：

String oldDate: 2018-06-18 13:07:27.624828+02
tempDate before format(): Mon Jun 18 13:17:51 CEST 2018
tempDate after format(): Mon Jun 18 13:17:51 CEST 2018
String newDate: 2018-06-18T13:17:51Z

如您所见，时间戳从13:07变为13:17。所有其他查询条目也显示出差异，在~2到10分钟之间变化。但是，当我重新运行查询时，每个差异都保持不变。 OP告诉我，所有涉及的系统都有同步时间，我不确定系统时间是否应该在这里发挥作用。

As you can see, the timestamp changed from 13:07 to 13:17. All the other queried entries also show a difference, varying between ~2 to 10 minutes. However, when I re-run the query, each difference stays the same. OPs told me that all involved systems have synchronised time and I'm not sure if system time should play a role here at all.

有人知道发生了什么吗？

Does someone know what is going on?

推荐答案

首先，我真的很困惑并且想到，你可能在 SimpleDateFormat 中发现了某种错误。您的代码可以缩减为以下行以显示相同的行为：

First, I was really puzzled and thought, you might have found some kind of bug in SimpleDateFormat. Your code can be reduced to the following lines to show the same behaviour:

SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSSSS");
String str = "2018-06-18 13:07:27.624828+02";
System.out.println(str);
System.out.println(format.parse(str));

结果：

2018-06-18 13:07:27.624828+02
Mon Jun 18 13:17:51 CEST 2018

解析后的日期对象又增加了10分钟（以及几秒钟）。

The parsed Date object got ten additional minutes (and some seconds).

仔细看看会发现问题 - 它不是JDK中的错误：

Taking a closer look reveals the problem - it is NOT a bug in JDK:

你的毫秒部分 624828 - 这些是六（！）位（不是三位）。 624828毫秒约为624秒，即10分24秒。
SimpleDateFormat 正确地总结了这个额外的秒和分钟。

Your millisecond-part is 624828 - these are six(!) digits (not three). 624828 milliseconds are about 624 seconds, which are 10 minutes and 24 seconds. The SimpleDateFormat correctly summed up this additional seconds and minutes.

还有什么不对：你的日期格式包含五位数的毫秒部分。

What's wrong too: Your date format contains five digits for the milliseconds part.

解决方案：

（新的） Java Time API 可以处理更大的一秒 - 并且还可以在不同的时区之间轻松转换：

The (new) Java Time API can handle larger fractions of a second - and also convert easily between different time zones:

String str = "2018-06-18 13:07:27.624828+02";
DateTimeFormatter pattern = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSSSSSx");
OffsetDateTime date = OffsetDateTime.parse(str, pattern);
System.out.println(date);
System.out.println(date.withOffsetSameInstant(ZoneOffset.UTC));

结果：

2018-06-18T13:07:27.624828+02:00
2018-06-18T11:07:27.624828Z

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