Java - 时间戳、Date、Calendar、SimpleDateFormat

Java

package com.ikoo.demo;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class DateUtil {
public static void main(String[] args) {
/**
* 时间戳
* 1.System.currentTimeMillis()
* 2.new Date().getTime()
* 3.Calendar.getInstance().getTimeInMillis()
* P.S.
*  Java获取时间戳精确到毫秒级，Unix中精确到秒级，所以Java获取的时间戳需要除以1000，就可以保证一致性
*  Calendar.getInstance().getTimeInMillis() 耗时最多，这是因为Canlendar要处理时区问题
*/
System.out.println("System.currentTimeMillis(): " + System.currentTimeMillis());
System.out.println("new Date().getTime(): " + new Date().getTime());
System.out.println("Calendar.getInstance().getTimeInMillis(): " + Calendar.getInstance().getTimeInMillis());
System.out.println("----------");

/**
* 时间戳（日期）转换自定义日期格式
*/
long timeStamp = System.currentTimeMillis();
System.out.println("System.currentTimeMillis(): " + timeStamp);
Date date = new Date();
System.out.println("new Date(): " + date);
long dateTimaStamp = date.getTime();
System.out.println("date.getTime(): " + date.getTime());
String formatDate0 = DateUtil.timeStampToFormatDate(System.currentTimeMillis(), "yyyy-MM-dd HH:mm:ss");
System.out.println("formatDate0: " + formatDate0);
String formatDate1 = DateUtil.timeStampToFormatDate(new Date(), "yyyy-MM-dd HH:mm:ss");
System.out.println("formatDate1: " + formatDate1);
String formatDate2 = DateUtil.timeStampToFormatDate(new Date().getTime(), "yyyy-MM-dd HH:mm:ss");
System.out.println("formatDate2: " + formatDate2);
String formatDate3 = DateUtil.timeStampToFormatDate(Calendar.getInstance().getTime(), "yyyy-MM-dd HH:mm:ss");
System.out.println("formatDate3: " + formatDate3);
}

/**
* 时间戳转换为格式化日期
*
* @param dateObj 时间对象
*                System.currentTimeMillis()
*                new Date()
*                new Date().getTime()
*                Calendar.getInstance().getTimeInMillis()
* @param pattern 日期格式
*                yyyy-MM-dd HH:mm:ss
*                yyyy/MM/dd HH:mm:ss
*                yyyy年MM月dd日 HH:mm:ss
* @return sdf.format(Object dateObj)
*/
public static String timeStampToFormatDate(Object dateObj, String pattern) {
SimpleDateFormat sdf = new SimpleDateFormat(pattern);
String formatDate = sdf.format(dateObj);
return formatDate;
}
}

System.currentTimeMillis(): 1503660334272
new Date().getTime(): 1503660334274
Calendar.getInstance().getTimeInMillis(): 1503660334299
----------
System.currentTimeMillis(): 1503660334328
new Date(): Fri Aug 25 19:25:34 CST 2017
date.getTime(): 1503660334328
formatDate0: 2017-08-25 19:25:34
formatDate1: 2017-08-25 19:25:34
formatDate2: 2017-08-25 19:25:34
formatDate3: 2017-08-25 19:25:34

Process finished with exit code 0