import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
import java.util.Objects;
import java.util.stream.Stream;

LocalDate startDate = cal.getStartDate();
LocalDate startExceptionDate = exceptions.get(0).getDate();

Stream.iterate(startDate, date -> date.plusDays(1))
                  .limit(ChronoUnit.DAYS.between(startDate, startExceptionDate))
                  .forEach(day -> sb.append("0"));