Localdatetime and string date conversion

LocalDateTime Turn into String

DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime time = LocalDateTime.now();
String localTime = df.format(time);
 be equal to 
String localTime = MyDateUtil.formatDateTimeDefault(time);

System.out.println("LocalDateTime Turn into String Type of time ："+localTime);

result ：

LocalDateTime Turn into String Type of time ：2017-09-30 10:40:06

String Turn into LocalDateTime

DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime ldt = LocalDateTime.parse("2017-09-28 17:07:05",df);
System.out.println("String The type of time turns into LocalDateTime："+ldt);

result ：

String The type of time turns into LocalDateTime：2017-09-28T17:07:05