LocalDateTime和String互转

1. LocalDateTime转String：

   LocalDateTime now = LocalDateTime.now();  
   DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"); 
   String timeStr = formatter.format(now);
   

2. String转LocalDateTime:

   DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");  
   LocalDateTime localDateTime = LocalDateTime.parse("2020-08-15 09:09:09", formatter);