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javadatetimejava-timethreetenbp

Convert java.time classes from java 8 to java 5

What do I do to use this lines of code with Java 5, as this code runs with Java 6 and 7 using threetenbp and runs on Java 8 directly:

// start date (set the time to start of day)
ZonedDateTime from = LocalDate.parse("2017-07-05").atStartOfDay(ZoneOffset.UTC);
// end date (set the time to 11 PM)
ZonedDateTime to = LocalDate.parse("2017-07-08").atTime(23, 0).atZone(ZoneOffset.UTC);

// get start and end timestamps
long start = from.toInstant().truncatedTo(ChronoUnit.MINUTES).toEpochMilli() / 1000;
long end = to.toInstant().truncatedTo(ChronoUnit.MINUTES).toEpochMilli() / 1000;
Solution

  • The ThreeTen Backport seems to work only in Java 6 and 7. I've tested with JDK 5 and it throws an UnsupportedClassVersionError.

    In Java 5, one alternative is the old SimpleDateFormat and Calendar classes:

    // set the formatter to UTC
TimeZone utc = TimeZone.getTimeZone("UTC");
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
sdf.setTimeZone(utc);

// parse and set the time to midnight
Calendar cFrom = Calendar.getInstance(utc);
cFrom.setTime(sdf.parse("2017-07-05"));
cFrom.set(Calendar.HOUR_OF_DAY, 0);
cFrom.set(Calendar.MINUTE, 0);
cFrom.set(Calendar.SECOND, 0);
cFrom.set(Calendar.MILLISECOND, 0);

// parse and set the time to 23:00
Calendar cTo = Calendar.getInstance(utc);
cTo.setTime(sdf.parse("2017-07-08"));
cTo.set(Calendar.HOUR_OF_DAY, 23);
cTo.set(Calendar.MINUTE, 0);
cTo.set(Calendar.SECOND, 0);
cTo.set(Calendar.MILLISECOND, 0);

// get the epoch second (get millis and divide by 1000)
long start = cFrom.getTimeInMillis() / 1000;
long end = cTo.getTimeInMillis() / 1000;

    The other alternative is to use Joda-Time, which has an API very similar to java.time:

    import org.joda.time.DateTime;
import org.joda.time.DateTimeZone;
import org.joda.time.LocalDate;
import org.joda.time.LocalTime;

DateTime from = LocalDate.parse("2017-07-05").toDateTimeAtStartOfDay(DateTimeZone.UTC);
DateTime to = LocalDate.parse("2017-07-08").toDateTime(new LocalTime(23, 0), DateTimeZone.UTC);

long start = from.getMillis() / 1000;
long end = to.getMillis() / 1000;

    This will produce the same values for start and end.

    Just a note: Joda-Time is in maintainance mode and is being replaced by the new APIs, so I don't recommend start a new project with it (unless you can't use the new API's, of course).
    Even in joda's website it says: "Note that Joda-Time is considered to be a largely “finished” project. No major enhancements are planned. If using Java SE 8, please migrate to java.time (JSR-310).".