Convert java.time classes from java 8 to java 5

Question

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;

Quick tip: the `Instant` class has the method `getEpochSecond()`, which returns the same as `toEpochMilli() / 1000`. And as you are setting the time with `atStartOfDay` and `atTime`, you don't need to truncate the minutes (the result will be the same, because the minutes, seconds and nanoseconds are already zero) — , Aug 08 '17 at 19:19
Seriously ask yourself if putting in the effort to port back to a long dead version of Java is really the best usage of your time and energy. I would rather look into upgrading whatever environment you have that is still in use and worth shipping new code to! — GhostCat, Aug 08 '17 at 19:26

score 2 · Accepted Answer · 2017-08-08T19:30:21.093

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).".

Another alternative: [JodaTime](http://www.joda.org/joda-time/), a library for dealing with times, and the spiritual father of JSR310. — cello, Aug 08 '17 at 19:22
@cello Indeed! I forgot it because Joda-Time is in maintainance mode and I stopped using it for new projects, but in this case it's a good choice. I've updated the answer, thanks a lot! — , Aug 08 '17 at 19:28

Convert java.time classes from java 8 to java 5

1 Answers1