[Java] 深入理解java long 存储时间戳

package cn.xbz;
 
import java.text.simpledateformat;
import java.time.*;
import java.time.format.datetimeformatter;
import java.util.calendar;
import java.util.date;
 
/**
 * @title 各种日期/时间对象转时间戳
 * @author xingbz
 * @createdate 2018-5-18
 */
public class datetime2millisdemo {
 
 private static final string format_str = "yyyy-mm-dd hh:mm:ss";
 
 public static void main(string[] args) {
  system.out.println("====== jdk7及之前 ======");
  long l1 = getmillis1();
  long l2 = date2millis(new date());
  long l3 = calendar2millis(calendar.getinstance());
  long l4 = string2millis(new simpledateformat(format_str).format(new date()) , format_str);//为了与以上几个保持一致
  system.out.println(l1 + "\n" + l2 + "\n" + l3 + "\n" + l4);//会有几毫秒的差别
 
  system.out.println("====== jdk8 ======");
  long l5 = getmillis2();
  long l6 = localdatetime2millis(localdatetime.now());
  long l7 = localdate2millis(localdate.now());
  long l8 = clock2millis(clock.systemutc());
  long l9 = zonedatetime2millis(zoneddatetime.now());
  long l10 = string2milliswithjdk8(localdatetime.now().format(datetimeformatter.ofpattern(format_str)) , format_str);//为了与以上几个保持一致
  system.out.println(l5 + "\n" + l6 + "\n" + l7 + "\n" + l8 + "\n" + l9 + "\n" + l10);//会有几毫秒的差别
 }
 
 /* jdk7及之前 */
 
 /** 获取时间戳 */
 public static long getmillis1() {
  return system.currenttimemillis();
 }
 
 /** date转时间戳 */
 public static long date2millis(date date) {
  return date.gettime();
 }
 
 /** calendar转时间戳 */
 public static long calendar2millis(calendar calendar) {
  return calendar.gettime().gettime();
 }
 
 /** 日期字符串转时间戳 */
 public static long string2millis(string datestr, string formatstr) {
  try {
   simpledateformat simpledateformat = new simpledateformat(formatstr);
   return simpledateformat.parse(datestr).gettime();
  } catch (exception e) {
   return 0l;
  }
 }
 
 /* jdk8 */
 
 /** 获取时间戳 */
 public static long getmillis2() {
  return instant.now().toepochmilli();
 }
 
 /** localdatetime转时间戳 */
 public static long localdatetime2millis(localdatetime localdatetime) {
  return localdatetime.toinstant(zoneoffset.ofhours(8)).toepochmilli();
 }
 
 /** localdate转时间戳 */
 public static long localdate2millis(localdate localdate) {
  return localdatetime.of(localdate, localtime.min).toinstant(zoneoffset.ofhours(8)).toepochmilli();
 }
 
 /** clock转时间戳 */
 public static long clock2millis(clock clock) {
  return clock.millis();
 }
 
 /** zonedatetime转时间戳(这个不常用吧~) */
 public static long zonedatetime2millis(zoneddatetime zoneddatetime) {
  return zoneddatetime.tolocaldatetime().toinstant(zoneoffset.ofhours(8)).toepochmilli();//!!!好费劲
 }
 
 /** string转时间戳(jdk8) */
 public static long string2milliswithjdk8(string datestr , string formatstr) {
  return localdatetime.parse(datestr , datetimeformatter.ofpattern(formatstr)).toinstant(zoneoffset.ofhours(8)).toepochmilli();
 }
}