DateTimeFormatter  是不变对象，线程安全

LocalDateTime now = LocalDateTime.now();
System.out.println(now);
final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS");
String timestr = now.format(dtf);
System.out.println(timestr);
LocalDateTime ldt = LocalDateTime.parse(timestr,dtf);
System.out.println(ldt);




2024-08-27T08:33:34.796
2024-08-27 08:33:34.796
2024-08-27T08:33:34.796