java - 如何使用Java获取当前日期/时间(How to get the current date/time in Java)

Question

用Java获取当前日期/时间的最佳方法是什么？

  ask by user496949 translate from so

Answer 1

It depends on what form of date / time you want:

(这取决于您想要的日期/时间形式：)

• If you want the date / time as a single numeric value, then System.currentTimeMillis() gives you that, expressed as the number of milliseconds after the UNIX epoch (as a Java long ).

  (如果您希望日期/时间为单个数值，那么System.currentTimeMillis()会为您提供该值，以UNIX纪元后的毫秒数表示（以Java long ）。)

  This value is a delta from a UTC time-point, and is independent of the local time-zone ... assuming that the system clock has been set correctly.

  (此值是UTC时间点的增量，并且与本地时区无关...假设系统时钟已正确设置。)

• If you want the date / time in a form that allows you to access the components (year, month, etc) numerically, you could use one of the following:

  (如果您希望日期/时间的格式允许您以数字方式访问组件（年，月等），则可以使用以下方式之一：)

  • new Date() gives you a Date object initialized with the current date / time.

    (new Date()为您提供了一个使用当前日期/时间初始化的Date对象。)

    The problem is that the Date API methods are mostly flawed ... and deprecated.

    (问题在于Date API方法大多存在缺陷……并且已过时。)

  • Calendar.getInstance() gives you a Calendar object initialized with the current date / time, using the default Locale and TimeZone .

    (Calendar.getInstance()使用默认的Locale和TimeZone为您提供一个使用当前日期/时间初始化的Calendar对象。)

    Other overloads allow you to use a specific Locale and/or TimeZone .

    (其他重载允许您使用特定的Locale和/或TimeZone 。)

    Calendar works ... but the APIs are still cumbersome.

    (日历可以工作...但是API仍然很麻烦。)

  • new org.joda.time.DateTime() gives you a Joda-time object initialized with the current date / time, using the default time zone and chronology.

    (new org.joda.time.DateTime()使用默认的时区和年表为您提供了一个使用当前日期/时间初始化的Joda-time对象。)

    There are lots of other Joda alternatives ... too many to describe here.

    (Joda还有许多其他替代方案，在此无法描述。)

    (But note that some people report that Joda time has performance issues.; eg Jodatime's LocalDateTime is slow when used the first time .)

    (（但请注意，有些人报告说Joda时间存在性能问题。例如，第一次使用Jodatime的LocalDateTime速度很慢 。）)

  • in Java 8, calling LocalDateTime.now() and ZonedDateTime.now() will give you representations ¹ for the current date / time.

    (在Java 8中，调用LocalDateTime.now()和ZonedDateTime.now()将为您提供当前日期/时间的表示形式¹ 。)

Prior to Java 8, most people who know about these things recommended Joda-time as having (by far) the best Java APIs for doing things involving time point and duration calculations.

(在Java 8之前，大多数了解这些事情的人都建议Joda-time拥有（到目前为止）最好的Java API来完成涉及时间点和持续时间计算的事情。)

With Java 8, this is no longer true.

(对于Java 8，这不再是事实。)

However, if you are already using Joda time in your codebase, there is no strong ² reason to migrate.

(但是，如果您已经在代码库中使用Joda time，则没有^2个强烈的理由进行迁移。)

---

^{1 - Note that LocalDateTime doesn't include a time zone.}

(^{1-请注意，LocalDateTime不包含时区。})

^{As the javadoc says: "It cannot represent an instant on the time-line without additional information such as an offset or time-zone."}

(^{正如javadoc所说： “如果没有其他信息（例如偏移量或时区），它就无法在时间轴上表示时刻。”})

^{2 - Your code won't break if you don't, and you won't get deprecation warnings.}

(^{2-如果不这样做，您的代码不会中断，也不会收到弃用警告。})

^{Sure, the Joda codebase will probably stop getting updates, but it is unlikely to need them.}

(^{当然，Joda代码库可能会停止获取更新，但是不太可能需要它们。})

^{No updates means stability and that is a good thing.}

(^{没有更新意味着稳定性，这是一件好事 。})

^{Also note that it is highly likely that if that someone will fix problems caused by regressions in the Java platform.}

(^{还要注意，很有可能有人会修复Java平台中由回归引起的问题。})