Compare FileTime and LocalDateTime

Question

How to compare FileTime and LocalDateTime objects in Java?

I want to compare a FileTime object from a file ( Files.getLastModifiedTime(item) ) with the current time ( LocalDateTime.now() ). But they are not compatible. How can I compare them?

Answer 1

The FileTime API is designed to encourage you to use Instant rather than LocalDateTime :

Instant now = Instant.now();
FileTime ft = Files.getLastModifiedTime(item);

if (ft.toInstant().isAfter(now)) { ... }

Note that Instant makes more sense than LocalDateTime in this case because it represents a unique instant "in real life". Whereas a LocalDateTime can be ambiguous, for example during Daylight Saving Time changes.

Answer 2

You can get instant from FileTime and create a LocalDateTime object using the instant.

Example

FileTime fileTime = Files.getLastModifiedTime(item);
LocalDateTime now = LocalDateTime.now();
LocalDateTime convertedFileTime = LocalDateTime.ofInstant(fileTime.toInstant(), ZoneId.systemDefault());

Now you can compare now & convertedFileTime.

Remember this is not taking into consideration the timezones which can change.

You can just work with Instant as well.

Answer 3

These are different time structures. You could use toInstant methods to convert them the same type. But LocalDateTime would require timezone. I guess that you just need current system clock time, so instead of LocalDateTime.now() you should use Clock.systemUTC().instant() , so you don't need to convert.

Moreover, if you inject Clock into your code, it will be much easier to mock from unit-tests rather than have dependency on a static methods which give you system time.

Answer 4

My practice when dealing with times, dates, time zones, etc... I usually convert those objects into Unix timestamp and then do needed operations.

long lastModifiedFileTime = Files.getLastModifiedTime(item).toMillis()/1000;
long now = LocalDateTime.now().toEpochSecond(ZoneOffset.UTC);

this would do it, but maybe you should consider using Instant instead of LocalDateTime, stuff gets overly complicated when dealing with time zones(depending on your requirements ofc).

long now = Instant.now().getEpochSecond();

Also you can use Instant objects

Instant now = Instant.now();
Instant lastModifiedFileTime = Files.getLastModifiedTime().toInstant();