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基于Calendar獲取當(dāng)前時(shí)間的性能比較

更新時(shí)間：2021年06月19日 17:01:58 作者：老周聊架構(gòu)

這篇文章主要介紹了Calendar獲取當(dāng)前時(shí)間的性能比較，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。如有錯(cuò)誤或未考慮完全的地方，望不吝賜教

除了獲取時(shí)間用Date和SimperFormat，還可用Calendar類方法獲取時(shí)間。

一、Calendar 類常用的獲取時(shí)間以及時(shí)區(qū)的方法：

Calendar calendar = Calendar.getInstance();
System.out.println("目前時(shí)間: " + calendar.getTime());
System.out.println("Calendar時(shí)區(qū): " + calendar.getTimeZone().getID());
System.out.println("user.timezone: " + System.getProperty("user.timezone"));
System.out.println("user.country: " + System.getProperty("user.country"));
System.out.println("默認(rèn)時(shí)區(qū): " + TimeZone.getDefault().getID());

運(yùn)行結(jié)果：

目前時(shí)間: Tue May 28 23:09:31 CST 2019
Calendar時(shí)區(qū): Asia/Shanghai
user.timezone: Asia/Shanghai
user.country: CN
默認(rèn)時(shí)區(qū): Asia/Shanghai

二、獲取當(dāng)前時(shí)間性能比較

long start1 = System.currentTimeMillis();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//設(shè)置日期格式
System.out.println(sdf.format(new Date()));// new Date()為獲取當(dāng)前系統(tǒng)時(shí)間
long end1 = System.currentTimeMillis();
System.out.println((end1 - start1) + "ms");

運(yùn)行結(jié)果：

2019-05-28 23:14:14
55ms

long start2 = System.currentTimeMillis();
Calendar calendar = Calendar.getInstance();//可以對(duì)每個(gè)時(shí)間域單獨(dú)修改
System.out.println(calendar.get(Calendar.YEAR) + "-" + calendar.get(Calendar.MONTH) + "-" + calendar.get(Calendar.DATE) + " " + calendar.get(Calendar.HOUR_OF_DAY) + ":" + calendar.get(Calendar.MINUTE) + ":" + calendar.get(Calendar.SECOND));
long end2 = System.currentTimeMillis();
System.out.println((end2 - start2) + "ms");

運(yùn)行結(jié)果：

2019-4-28 23:15:22
36ms

顯然，第二種的Calendar獲取當(dāng)前時(shí)間的性能比SimpleDateFormat的要快

三、獲取零點(diǎn)時(shí)間的性能比較

long start3 = System.currentTimeMillis();
Calendar calendar = Calendar.getInstance();
calendar.setTime(new Date());
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
Date zero = calendar.getTime();
long end3 = System.currentTimeMillis();
System.out.println(zero);
System.out.println((end3 - start3) + "ms");

運(yùn)行結(jié)果：

Tue May 28 00:00:00 CST 2019
34ms

long start4 = System.currentTimeMillis();
long current = System.currentTimeMillis();
long zero = current/(1000*3600*24)*(1000*3600*24) - TimeZone.getDefault().getRawOffset();
System.out.println(zero);
long end4 = System.currentTimeMillis();
System.out.println((end4 - start4) + "ms");

運(yùn)行結(jié)果：

1558972800000
11ms

這里current表示毫秒，那么除以了1000 * 3600 * 24得到天數(shù),但是可能不是整數(shù)天，但是因?yàn)閠是long型，那么小數(shù)部分沒有了，再去乘以1000 * 3600 * 24，就變成整數(shù)天數(shù)所對(duì)應(yīng)的毫秒了。

TimeZone.getDefault().getRawOffset() 計(jì)算夏令時(shí)和返回當(dāng)前時(shí)區(qū)與格林尼治時(shí)間的偏差。

顯然，這里獲取零點(diǎn)時(shí)間強(qiáng)烈推薦第二種方法，性能比第一種高三倍左右。

Calendar獲取當(dāng)前年份、月份、日期

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class TestDate {
    /**
     * 獲取當(dāng)前年份、月份、日期  
     * @param args
     */
    public static void main(String[] args) {
        Calendar cale = null;  
        cale = Calendar.getInstance();  
        int year = cale.get(Calendar.YEAR);  
        int month = cale.get(Calendar.MONTH) + 1;  
        int day = cale.get(Calendar.DATE);  
        int hour = cale.get(Calendar.HOUR_OF_DAY);  
        int minute = cale.get(Calendar.MINUTE);  
        int second = cale.get(Calendar.SECOND);  
        int dow = cale.get(Calendar.DAY_OF_WEEK);  
        int dom = cale.get(Calendar.DAY_OF_MONTH);  
        int doy = cale.get(Calendar.DAY_OF_YEAR);  
  
        System.out.println("Current Date: " + cale.getTime());  
        System.out.println("Year: " + year);  
        System.out.println("Month: " + month);  
        System.out.println("Day: " + day);  
        System.out.println("Hour: " + hour);  
        System.out.println("Minute: " + minute);  
        System.out.println("Second: " + second);  
        System.out.println("Day of Week: " + dow);  
        System.out.println("Day of Month: " + dom);  
        System.out.println("Day of Year: " + doy);  
  
        // 獲取當(dāng)月第一天和最后一天  
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
        String firstday, lastday;  
        // 獲取前月的第一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 0);  
        cale.set(Calendar.DAY_OF_MONTH, 1);  
        firstday = format.format(cale.getTime());  
        // 獲取前月的最后一天  
        cale = Calendar.getInstance();  
        cale.add(Calendar.MONTH, 1);  
        cale.set(Calendar.DAY_OF_MONTH, 0);  
        lastday = format.format(cale.getTime());  
        System.out.println("本月第一天和最后一天分別是 ： " + firstday + " and " + lastday);  
  
        // 獲取當(dāng)前日期字符串  
        Date d = new Date();  
        System.out.println("當(dāng)前日期字符串1：" + format.format(d));  
        System.out.println("當(dāng)前日期字符串2：" + year + "/" + month + "/" + day + " "  
                + hour + ":" + minute + ":" + second);  
    }
}

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