使用 SimpleDateFormat 将字符串转换为日期返回随机日期 [英] Converting String to Date using SimpleDateFormat is returning random date

问题描述

我对以下行为感到非常困惑.我从一个方法返回 2 个日期作为字符串:

I'm very confused by the following behaviour. I am returning 2 dates as Strings from a method:

 getLastSupplierFlightResults()

我添加了一个屏幕截图，显示返回的日期分别为2018-06-20 00:00:00"和2018-06-24 00:00:00"，并留下调试跟踪以显示值.

I have added a screenshot showing the returned dates as "2018-06-20 00:00:00" and "2018-06-24 00:00:00" respectively and left the debug trace in to show the values.

我只是想将日期转换为 20180620 格式.

I simply want to convert the dates into 20180620 format.

方法:

.withStartDate()
.withEndDate()

...接受字符串值

我不明白Wed Dec 06 00:00:00 GMT 2017"的日期是从哪里来的?这是最终作为 20171206 传递给 .withStart 和 .withEnd 方法的值.

What I don't understand is where the date "Wed Dec 06 00:00:00 GMT 2017" is coming from? This is the value that ends up being passed into the .withStart and .withEnd methods as 20171206.

一如既往，可能有一种更简单的方法来实现我的目标.

As always, there is probably a simpler way of achieving my aims.

推荐答案

您正在使用格式模式字符串 yyyyMMdd.您正在解析日期时间字符串 2018-06-20 00:00:00.

You are using the format pattern string yyyyMMdd. You are parsing the date-time string 2018-06-20 00:00:00.

2018 匹配 yyyy.MM 表示月份应该是两个字符，所以取-0 作为月份.而 -0 或者只是 0 被取为 2018 年第 1 个月的前一个月，即 2017 年 12 月.最后将 6 取为该月的第几天.它也应该是两个字符，但由于只有一个数字，SimpleDateFormat 就这样解决了.字符串的其余部分被默认忽略.

2018 matches yyyy. MM means that month should be two chars, so -0 is taken for the month. And -0 or just 0 is taken to be the month before month 1 of 2018, that is, December 2017. Finally 6 is taken as the day of month. It should have been two chars too, but since there is only one digit, SimpleDateFormat settles with that. The remainder of the string is tacitly ignored.

解析另一个字符串时会发生完全相同的事情.

Exactly the same thing happens when parsing the other string.

简而言之，这是一个早已过时的SimpleDateFormat 类:为了友好和乐于助人，它产生了最令人不快和令人困惑的惊喜.在您希望它会告诉您出现问题的地方，它只是假装一切都很好.这是这个类被认为是麻烦的主要原因之一，也是为什么在 4 年前 Java 8 中替代旧类的原因.所以永远不要再使用 SimpleDateFormat.

It’s the long outdated SimpleDateFormat class in a nutshell: In its attempts to be friendly and helpful it produces the most unpleasant and confusing surprises. Where you would have wished it would tell you something is wrong, it just pretends that everything is fine. It’s one of the main reasons that this class is considered troublesome, and why the replacement for the old classes came out with Java 8 more than 4 years ago. So just never use SimpleDateFormat again.

而是查看 java.time 及其 DateTimeFormatter.

也不要从数据库中以字符串的形式获取日期值.根据查询返回的数据类型，获取 LocalDateTime 或 LocalDate 对象.这将使您完全免于解析.

Also don’t get date values as strings from your database. Depending on the datatype that the query returns get either a LocalDateTime or a LocalDate object. This will free you completely from parsing.

链接: Oracle 教程:日期时间解释如何使用 java.time.

这篇关于使用 SimpleDateFormat 将字符串转换为日期返回随机日期的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！