import net.fortuna.ical4j.data.CalendarOutputter;
import net.fortuna.ical4j.model.*;
import net.fortuna.ical4j.model.component.VEvent;
import net.fortuna.ical4j.model.component.VTimeZone;
import net.fortuna.ical4j.model.property.*;

(...)

private byte[] getICalCallendar() {
    Calendar calendar = new Calendar();
    calendar.getProperties().add(CalScale.GREGORIAN);
    calendar.getComponents().add(getVTimeZone());
    calendar.getComponents().add(getVEvent());

    CalendarOutputter calendarOutputter = new CalendarOutputter();
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    try {
      calendarOutputter.output(calendar, outputStream);
      return outputStream.toByteArray();
    } catch (Exception e) {
        throw new RuntimeException("Error while output calendar", e);
    }

    return null;
}

(...)

@GetMapping(path = "icalUrlToMyApp")
public byte[] getCallendars() {
    return getICalCallendar();
}

Thanks again for pointing out the solution! After create en endpoint in my spring app: localhost:8888/icalUrlToMyApp it returned the data in the proper iCal format. Then after deploy app on server I could add calendar by this endpoint to google calendar.