Play with Java 8 Dates, new time API and catching invalid dates, getting the first Sunday in each Month

main.java

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.sql.*;
import java.time.*;
import static java.time.temporal.TemporalAdjusters.*;

public class Main {

	public static Date isValidDate(String inDate, String formatString) {
		Date dateTime = null;
		
		SimpleDateFormat dateFormat = new SimpleDateFormat(formatString);
		dateFormat.setLenient(false);
		
		try {
			dateTime = dateFormat.parse(inDate.trim());
		} catch (ParseException pe) {
			System.out.println(pe.getMessage());
			return null;
		}
		return dateTime;
	}

	public static Date getFirstSundayInMonth(Date date) {

		// Time Zone
		ZoneId defaultZoneId = ZoneId.systemDefault();
		System.out.println("System Default TimeZone : " + defaultZoneId);
		
		//1. Convert Date -> Instant
		Instant instant = date.toInstant();
		System.out.println("instant : " + instant); 
		
		//2. Instant + system default time zone + toLocalDate() = LocalDate
			LocalDate localDate = instant.atZone(defaultZoneId).toLocalDate();
			System.out.println("localDate : " + localDate);
		
		
		LocalDateTime firstSundayOfMonth = LocalDateTime
									.ofInstant(date.toInstant(), ZoneId.systemDefault())
									.with(firstDayOfMonth())
									.with(nextOrSame(DayOfWeek.SUNDAY));
		System.out.println("First Sunday: " + firstSundayOfMonth); 
		
		instant = firstSundayOfMonth.atZone(ZoneId.systemDefault()).toInstant();
		Date newDateTime = Date.from(instant);
		return newDateTime;
	}

	public static void main(String[] args) {

		System.out.println(isValidDate("2004-02-29","yyyy-MM-dd"));
		System.out.println(isValidDate("2005-02-29","yyyy-MM-dd"));
		System.out.println(isValidDate("2005-04-31","yyyy-MM-dd"));
		System.out.println(isValidDate("31/04/2005","dd/MM/yyyy"));
		System.out.println(isValidDate("31/03/2005","dd/MM/yyyy"));
		
		Date dateTime,dateTime1, dateTime2,dateTime3;
		
		SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
		try {
			dateTime = dateFormat.parse("2005-04-31");
			dateTime1 = dateFormat.parse("2017-10-31");
			dateTime2 = dateFormat.parse("2017-10-2"); 
			dateTime3 = dateFormat.parse("2017-11-5"); 
			
		} catch (ParseException pe) {
					System.out.println(pe.getMessage());
					return;
		}
				
		getFirstSundayInMonth(dateTime);
		getFirstSundayInMonth(dateTime1);
		getFirstSundayInMonth(dateTime2);
		getFirstSundayInMonth(dateTime3);
		return;	
	}
}