如何计算java中事件的运行时间?

What's a simple/easy way to access the system clock using Java, so that I can calculate the elapsed time of an event?

使用Java访问系统时钟的简单/简单方法是什么，以便我可以计算事件的运行时间?

6 个解决方案

#1

I would avoid using System.currentTimeMillis() for measuring elapsed time. currentTimeMillis() returns the 'wall-clock' time, which may change (eg: daylight savings, admin user changing the clock) and skew your interval measurements.

我将避免使用System.currentTimeMillis()来度量运行时间。currentTimeMillis()返回“wall-clock”时间，该时间可能会改变(例如:夏令时，管理用户更改时钟)，并会影响间隔测量。

System.nanoTime(), on the other hand, returns the number of nanoseconds since 'some reference point' (eg, JVM start up), and would therefore not be susceptible to system clock changes.

另一方面，system . nanotime()返回自“某个参考点”(例如JVM启动)以来的纳秒数，因此不受系统时钟更改的影响。

#2

This is some sample code.

这是一些示例代码。

long startTime = System.currentTimeMillis();
// Run some code;
long stopTime = System.currentTimeMillis();

System.out.println("Elapsed time was " + (stopTime - startTime) + " miliseconds.");

#3

Apache Commons-Lang also has the StopWatch class suited just for your purpose. It uses System.currentTimeMillis(), so you'll still have resolution problems, but you can pause and do lap times and such. I use it as standard now for event stats.

Apache Commons-Lang也有适合您使用的StopWatch类。它使用System.currentTimeMillis()，因此您仍然会有解决问题的问题，但是您可以暂停并执行圈时间等等。我现在将它作为事件统计的标准。

http://commons.apache.org/lang/api-release/org/apache/commons/lang/time/StopWatch.html

http://commons.apache.org/lang/api-release/org/apache/commons/lang/time/StopWatch.html

#4

The Answer by Leigh is correct.

李的回答是正确的。

java.time

Java 8 and later has the java.time framework built in.

Java 8以及以后的Java。建成的时间框架。

An Instant is a moment on the timeline in UTC with nanosecond resolution (up to 9 digits of a decimal fraction of a second). The now method grabs the current date-time moment.

瞬间是UTC时间轴上的时刻，具有纳秒分辨率(最高可达9位，小数几分之一秒)。now方法获取当前日期-时间时刻。

Instant now = Instant.now();

2016-03-12T04:29:39.123Z

2016 - 03 - 12 - t04:29:39.123z

You can calculate the elapsed time between a pair of Instant objects as a Duration. The duration uses nanosecond resolution with a maximum value of the seconds that can be held in a long. This is greater than the current estimated age of the universe.

您可以计算两个瞬时对象之间的运行时间。持续时间使用纳秒分辨率，最大的值为秒，可以保持很长时间。这比目前估计的宇宙年龄要大。

Duration duration = Duration.between( startInstant , stopInstant );

The default output of Duration::toString is in standard ISO 8601 format. You can also ask for a total count of nanoseconds (toNanos) or milliseconds (toMillis), as well as other amounts.

持续时间的默认输出是::toString是标准ISO 8601格式。您还可以要求总数纳秒(toNanos)或毫秒(toMillis)，以及其他数量。

Java 8

In Java 8, fetching the current moment resolves only to millisecond resolution (up to 3 digits of a decimal fraction of a second). So while the java.time classes can store nanoseconds they can only determine the current moment with milliseconds. This limitation is due to a legacy issue (the default Clock implementation uses System.currentTimeMillis()).

在Java 8中，获取当前力矩只能解析成毫秒级的分辨率(最高可达3位，即小数几分之一秒)。因此,尽管java。时间类可以存储纳秒，它们只能用毫秒来确定当前时刻。这个限制是由于遗留问题(默认的时钟实现使用System.currentTimeMillis()))。

Java 9

In Java 9 and later, the default Clock implementation can determine the current moment in up to nanosecond resolution. Actually doing so depends on the fineness of your computer’s clock hardware.

在Java 9和以后的版本中，默认的时钟实现可以在高达纳秒的分辨率下确定当前时刻。实际上，这取决于你计算机时钟硬件的精确性。

See this OpenJDK issue page for more info: Increase the precision of the implementation of java.time.Clock.systemUTC()

有关更多信息，请参见OpenJDK问题页面:增加java.time.Clock.systemUTC()实现的精确性

Micro Benchmark

If your purpose is benchmarking, be sure to look at other Questions such as:

如果你的目标是基准测试，一定要看看其他的问题，比如:

• How do I write a correct micro-benchmark in Java?
• 如何用Java编写正确的微基准?
• Create quick/reliable benchmark with java?
• 使用java创建快速/可靠的基准?

Frameworks are available to assist with short-duration benchmarking.

可以使用框架来辅助短期基准测试。

#5

java.lang.System.currentTimeMillis() or java.lang.System.nanoTime() ought to work to measure elapsed time.

nanotime()应该用于度量流逝时间。

#6

Here is a small StopWatch class I wrote using the System.nanoTime() as suggested in the answer from Leigh:

下面是我使用System.nanoTime()编写的一个小型秒表类，正如Leigh给出的答案所示:

public class StopWatch {
    // Constructor
    public StopWatch() {
    }

    // Public API
    public void start() {
        if (!_isRunning) {
            _startTime = System.nanoTime();
            _isRunning = true;
        }
    }

    public void stop() {
        if (_isRunning) {
            _elapsedTime += System.nanoTime() - _startTime;
            _isRunning = false;
        }
    }

    public void reset() {
        _elapsedTime = 0;
        if (_isRunning) {
            _startTime = System.nanoTime();
        }
    }

    public boolean isRunning() {
        return _isRunning;
    }

    public long getElapsedTimeNanos() {
        if (_isRunning) {
            return System.nanoTime() - _startTime;
        }
        return _elapsedTime;
    }

    public long getElapsedTimeMillis() {
        return getElapsedTimeNanos() / 1000000L;
    }

    // Private Members
    private boolean _isRunning = false;
    private long _startTime = 0;
    private long _elapsedTime = 0;
}