Parsing timestamp as LocalDateTime

问题

I want to parse a timestamp in the form of yyyy-MM-dd'T'HH:mm:ss as LocalDateTime. When doing so, it strips the seconds if they are 00.

As described here, I need to use a custom formatter

LocalDateTime date = LocalDateTime.parse("2008-10-02T12:30:00");
DateTimeFormatter f = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss");

String dateString = date.toString();
String dateFormatted = date.format(f);

System.out.println(dateString); // 2008-10-02T12:30

This one works, but it returns a String:

System.out.println(dateFormatted); // 2008-10-02T12:30:00

When I parse the string to LocalDateTime it strips the 00 again:

LocalDateTime dateLDT = LocalDateTime.parse(dateFormatted, f);
System.out.println(dateLDT); // 2008-10-02T12:30

So how can I parse a date as LocalDateTime, instead of String, and keep the 00 at the end?

回答1:

You should expect a difference in output between

LocalDateTime dateLDT = LocalDateTime.parse(dateFormatted, f);
System.out.println(dateLDT);

And

System.out.println(dateLDT.format(f)) //or f.format(dateLDT)

System.out.println(dateLDT); prints the value of dateLDT.toString(), which is not expected to produce the same output as your pattern.

When you look at LocalDateTime.toString(), you'll see that it delegates the time part to LocalTime.toString(), which prints seconds conditionally:

public String toString() {
    ...
    if (secondValue > 0 || nanoValue > 0) {
        buf.append(secondValue < 10 ? ":0" : ":").append(secondValue);
        ...
        }
    }
    return buf.toString();
}

It simply omits the seconds field if its value is 0.

What you need to do in this case is always use a DateTimeFormatter to format your date if you have to be certain about the output/input format.

回答2:

Every date object has seconds. Wether or not it chooses to display them with the default toString implementation does not matter. If you want a specific format you always need to use a formatter.

If you want to see the seconds, either use a proper formatter or set a breakpoint and inspect the object. Looking at any toString implementation of anything is never guaranteed to display anything useful or represent the actual object state. The object could just return a random date string.

For now you can just use date, it is perfectly fine, it has seconds.

来源：https://stackoverflow.com/questions/54941872/parsing-timestamp-as-localdatetime

标签

java

string

date

formatting

localdate