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);
}