Java8的DateTimeFormatter与SimpleDateFormat的区别详解

package com.main;

import java.text.DateFormat;

import java.text.SimpleDateFormat;

import java.time.LocalDate;

import java.time.LocalDateTime;

import java.time.format.DateTimeFormatter;

import java.util.Date;

public class Main {

   public static void main(String args[]){

     //解析日期

     String dateStr= "2016年10月25日" ;

     DateTimeFormatter formatter = DateTimeFormatter.ofPattern( "yyyy年MM月dd日" );

     LocalDate date= LocalDate.parse(dateStr, formatter);

     //日期转换为字符串

     LocalDateTime now = LocalDateTime.now();

     DateTimeFormatter format = DateTimeFormatter.ofPattern( "yyyy年MM月dd日 hh:mm a" );

     String nowStr = now .format(format);

     System.out.println(nowStr);

     //ThreadLocal来限制SimpleDateFormat

     System.out.println(format( new Date()));

   }

   //要在高并发环境下能有比较好的体验，可以使用ThreadLocal来限制SimpleDateFormat只能在线程内共享，这样就避免了多线程导致的线程安全问题。

   private static ThreadLocal<DateFormat> threadLocal = new ThreadLocal<DateFormat>() {

     @Override

     protected DateFormat initialValue() {

       return new SimpleDateFormat( "yyyy-MM-dd HH:mm:ss" );

     }

   };

   public static String format(Date date) {

     return threadLocal.get().format(date);

   }

}

public static String getDateTimeAsString(LocalDateTime localDateTime, String format) {

   DateTimeFormatter formatter = DateTimeFormatter.ofPattern(format);

   return localDateTime.format(formatter);

}

public static LocalDateTime getDateTimeOfTimestamp( long timestamp) {

   Instant instant = Instant.ofEpochMilli(timestamp);

   ZoneId zone = ZoneId.systemDefault();

   return LocalDateTime.ofInstant(instant, zone);

}

public static long getTimestampOfDateTime(LocalDateTime localDateTime) {

   ZoneId zone = ZoneId.systemDefault();

   Instant instant = localDateTime.atZone(zone).toInstant();

   return instant.toEpochMilli();

}

public static LocalDateTime parseStringToDateTime(String time, String format) {

   DateTimeFormatter df = DateTimeFormatter.ofPattern(format);

   return LocalDateTime.parse(time, df);

}