LocalDate date = LocalDate.now();
TemporalField woy = WeekFields.of(Locale.getDefault()).weekOfWeekBasedYear();
int weekNumber = date.get(woy);
LocalDate date = ...;
// Or use a specific locale, or configure your own rules
WeekFields weekFields = WeekFields.of(Locale.getDefault());
int weekNumber = date.get(weekFields.weekOfWeekBasedYear());