Using java.time.Clock.offset to increment in time with an arbitrary starting time-of-day

问题

I want a clock that is set to an arbitrary time-of-day, then ticks in one-second increments.

For example, start with "14:55:20". Then my app should output "14:55:20", "14:55:21", "14:55:22" and so on in one-second ticks.

It would seem that Clock.offset is meant to do just this. To quote the doc:

Obtains a clock that returns instants from the specified clock with the specified duration added

So I tried the following:

LocalTime localTime = LocalTime.parse( "14:55:20" );
OffsetDateTime odt = OffsetDateTime.now( ZoneOffset.UTC ).with( localTime );
Duration duration = Duration.between( odt.toInstant() , Instant.now() );
Clock clock = Clock.offset( Clock.systemUTC() , duration );

System.out.println( "odt = " + odt );
System.out.println( "duration = " + duration );

for ( int i = 1 ; i < 10 ; i++ )
{
    LocalTime lt = OffsetDateTime.now( clock ).truncatedTo( ChronoUnit.SECONDS ).toLocalTime();
    System.out.println( "localTime = " + lt );
    try
    {
        Thread.sleep( TimeUnit.SECONDS.toMillis( 1 ) );
    }
    catch ( InterruptedException e )
    {
        e.printStackTrace();
    }
}

My initial starting point with odt seems right. But then my calls to OffsetDateTime.now( clock ) are not producing the desired outcome.

odt = 2019-10-31T14:55:20Z

duration = PT-10H-29M-4.832902S

localTime = 17:57:10

localTime = 17:57:11

localTime = 17:57:12

➥ I am I not properly using Clock.offset? Or am I misunderstanding some concept here?

回答1:

The duration is the wrong way:

Duration duration = Duration.between( Instant.now(), odt.toInstant() ); // Flipped arguments

Output

odt = 2019-10-31T14:55:20Z
duration = PT8H1M41.0216146S
localTime = 14:55:20
localTime = 14:55:21
localTime = 14:55:22
localTime = 14:55:23
localTime = 14:55:24
localTime = 14:55:25
localTime = 14:55:26
localTime = 14:55:27
localTime = 14:55:28

回答2:

I think you can simply check if the number of second have changed, for example you can do this :

     public static void main(String[] args) {
        // hour of launch
        String startTime = getTime();
        // actual time;
        String time = getTime();
        // elapsed time in seconds.
        int elapsedTime = 0;

        while (true) {
            if(!time.equals(getTime())) {
                time = getTime();
                // Output actual time.
                System.out.println(time);
                elapsedTime += 1;         
            }
        }               
    }

    public static String getTime() {
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Date date = new Date();
        return dateFormat.format(date); 
    }

来源：https://stackoverflow.com/questions/58637015/using-java-time-clock-offset-to-increment-in-time-with-an-arbitrary-starting-tim

标签

java

clock