任何使用时间戳的优秀高性能java库？

Question

我要寻找高性能的Java库，它提供了一些方法，可以让我得到：

1. 当前的小时（0-24）
2. 当天（1-31）
3. 本周（1 52）
4. 本月（1-12）
5. 当前季节（1-4）
6. 本年度（YYYY或YY）

性能对我来说是最重要的问题。这就是为什么我不能使用标准的Calendar类。最好的解决方案是在不创建新对象的情况下进行所有计算。

增加：为了澄清我会再提一次：更多的是每秒100000次操作。

Answer 1

你实际上可以使用excellant joda时间库来做到这一点。 joda中的Chronology实现提供了DateTime getHourgetDay类型方法背后的逻辑。如果您希望跳过创建DateTime时刻，直接使用它没有问题。

long msSinceEpoch = System.currentTimeMillis(); 

Chronology chronology = ISOChronology.getInstanceUTC() // This can be static 

chronology.hourOfDay().get(msSinceEpoch); 
chronology.dayOfMonth().get(msSinceEpoch); 
chronology.weekOfWeek().get(msSinceEpoch); 
chronology.monthOfYear().get(msSinceEpoch); 
chronology.years().get(msSinceEpoch); 

会话不是joda有概念的东西。根据你自己的规则，你必须从月份开始。

见joda-time documentation on Chronology

Answer 2

你确定Calendar太慢还是你相信它？你有没有尺寸呢？在Java中创建新对象相当便宜。保持它们很昂贵。

也就是说，要么尝试Joda Time，要么将Java代码中的算法复制到静态辅助方法中。

Answer 3

仅使用一个对象，并更新它的时候，像这样：

Date d = new Date(); 
... 
d.setTime(System.currentTimeMillis()); 

Answer 4

您可以使用java.util.Calander，如果不满意，你可以使用可能Joda Time。

这可以帮助你。

Answer 5

您可以使用Joda Time因为它比日历快得多，而做到这一点：

LocalDateTime now = new LocalDateTime(); // automatically points to current datetime. 
int hour = now.getHourOfDay(); 
int day = now.getDayOfMonth(); 
int week = now.getWeekOfWeekyear(); 
int month = now.getMonthOfYear(); 
int year = now.getYear(); 
int season = getSeason(day, month); 

的getSeason（）很容易实现。没有任何解决方案可以在不创建任何对象的情况下完成这一切。顺便说一句，为什么你需要这么多的表演？！？！

Answer 6

您可以获取当前时间，并通过除法和余数计算当前小时数，分钟数，秒数，毫秒数。日，月，年只是每天更换一次，所以您只需在计算时间内进行计算。

可以使用缓存的日/月/年计算，其余的亚微秒的时间，而无需创建对象（超过每天一次）

import java.util.Calendar; 
import java.util.TimeZone; 

public class Daytime { 
    private static final long HOUR_MS = 3600*1000; 

    public short year; 
    public byte month, day; 
    public byte hour, min, sec; 
    public short millis; 

    private long lastMillis = Integer.MIN_VALUE; 
    private final TimeZone timeZone; 
    private long timeOffset; 

    public Daytime() { 
     timeZone = TimeZone.getTimeZone("UTC"); 
     now(); 
    } 

    public Daytime(TimeZone timeZone) { 
     this.timeZone = timeZone; 
     now(); 
    } 

    public void now() { 
     long now = System.currentTimeMillis() + timeOffset; 
     if (now == lastMillis) return; 
     long cachePeriod = now/HOUR_MS; 
     // could the day have changed? 
     if (cachePeriod != lastMillis/HOUR_MS) { 
      timeOffset = timeZone.getOffset(now); 
      Calendar cal = Calendar.getInstance(timeZone); 
      year = (short) cal.get(Calendar.YEAR); 
      month = (byte) cal.get(Calendar.MONTH); 
      day = (byte) cal.get(Calendar.DAY_OF_MONTH); 
      hour = (byte) cal.get(Calendar.HOUR); 
     } 
     millis = (short) (now % 1000); 
     now /= 1000; 
     sec = (byte) (now % 60); 
     now /= 60; 
     min = (byte) (now % 60); 
    } 

    public static void main(String... args) { 
     Daytime dt = new Daytime(); 
     long start = System.nanoTime(); 
     final int runs = 10 * 1000 * 1000; 
     for(int i=0;i< runs;i++) 
      dt.now(); 
     long time = System.nanoTime() - start; 
     System.out.printf("Daytime.now() took %.3f micro-seconds on average%n", time/1e3/runs); 
    } 
} 

打印

Daytime.now() took 0.287 micro-seconds on average 

关于夏令时变化的发生有多种假设。您可能需要更改检查周期以适应您的需要。

Answer 7

注意Calendar.getInstance是相当昂贵的，但你可以通过调用该方法一次，并重新使用（除非你需要每个线程的日历：日历不是线程安全的），通常得到您的日历对象。

Answer 8

我已经所以，现在，我终于下载了它，并给它一个尝试了解约达时间那么多帖子。

Gareth Davis的回答已经被接受，我对此没有任何问题。但我很想知道Joda Time在哪里做出了改变。

基于这个问题和接受的答案，我做了一个类来比较JDK Calendar和Joda Time Chronology的执行时间。

我发现日历实现的运行速度始终更快，速度并不快。

import java.util.Calendar; 
import java.util.Date; 

import org.joda.time.Chronology; 
import org.joda.time.chrono.ISOChronology; 


public class CalendarTest { 

    private static final int ITERATIONS = 1000000; 

    public static void main(String[] args) { 
     for (int i = 0; i < 10; i++) { 
      jdkCalendar(); 
      jodaChronology(); 
     } 
    } 

    private static void jdkCalendar() { 
     long start = System.currentTimeMillis(); 
     Calendar c = Calendar.getInstance(); 
     int hourOfDay = 0; 
     int dayOfMonth = 0; 
     int weekOfYear = 0; 
     int month = 0; 
     int year = 0; 
     for (int i = 0; i < ITERATIONS; i++) { 
      c.setTimeInMillis(System.currentTimeMillis()); 
      hourOfDay = c.get(Calendar.HOUR_OF_DAY); 
      dayOfMonth = c.get(Calendar.DAY_OF_MONTH); 
      weekOfYear = c.get(Calendar.WEEK_OF_YEAR); 
      month = c.get(Calendar.MONTH); 
      year = c.get(Calendar.YEAR); 
     } 
     long duration = System.currentTimeMillis() - start; 
     System.err.printf("jdk: duration %d, hourOfDay: %d, dayOfMonth: %d, weekOfYear: %d, month: %d, year: %d\n", duration, hourOfDay, dayOfMonth, weekOfYear, month, year); 
    } 

    private static void jodaChronology() { 
     long start = System.currentTimeMillis(); 
     Chronology chronology = ISOChronology.getInstanceUTC(); // This can be static 
     int hourOfDay = 0; 
     int dayOfMonth = 0; 
     int weekOfYear = 0; 
     int month = 0; 
     int year = 0; 
     for (int i = 0; i < ITERATIONS; i++) { 
      long msSinceEpoch = System.currentTimeMillis(); 
      hourOfDay = chronology.hourOfDay().get(msSinceEpoch); 
      dayOfMonth = chronology.dayOfMonth().get(msSinceEpoch); 
      weekOfYear = chronology.weekOfWeekyear().get(msSinceEpoch); 
      month = chronology.monthOfYear().get(msSinceEpoch); 
      year = chronology.years().getValue(msSinceEpoch); 
     } 
     long duration = System.currentTimeMillis() - start; 
     System.err.printf("joda: duration %d, hourOfDay: %d, dayOfMonth: %d, weekOfYear: %d, month: %d, year: %d\n", duration, hourOfDay, dayOfMonth, weekOfYear, month, year); 
    } 

} 

输出示例：

jdk: duration 1714, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 2099, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 377, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 689, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 340, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 680, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 330, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 653, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 326, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 596, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 337, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 620, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 471, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 590, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 326, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 591, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 336, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 595, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41 
jdk: duration 327, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 5, year: 2011 
joda: duration 560, hourOfDay: 12, dayOfMonth: 24, weekOfYear: 25, month: 6, year: 41