Java 특정 날짜, 시간부터 현재까지 몇초(분) 지났는지 구하기

Java 특정 날짜, 시간부터 현재까지 몇초(분) 지났는지 구하기

방법1

public void test_calendar(){
    String game_started_date = "2015-09-03";
    String game_started_time = "16:00:00";

    Calendar game_start_calendar = Calendar.getInstance();
    game_start_calendar.set(
            Integer.parseInt(game_started_date.substring(0, 4))
            , Integer.parseInt(game_started_date.substring(5, 7)) - 1
            , Integer.parseInt(game_started_date.substring(8, 10))
            , Integer.parseInt(game_started_time.substring(0, 2))
            , Integer.parseInt(game_started_time.substring(3, 5))
            , Integer.parseInt(game_started_time.substring(6, 8))
    );

    Calendar now_calendar = Calendar.getInstance();


    System.out.println(game_started_date.substring(0, 4));
    System.out.println(game_started_date.substring(5, 7));
    System.out.println(game_started_date.substring(8, 10));
    System.out.println(game_started_time.substring(0, 2));
    System.out.println(game_started_time.substring(3, 5));
    System.out.println(game_started_time.substring(6, 8));

    System.out.println(game_start_calendar);
    System.out.println(now_calendar);
    System.out.println(game_start_calendar.getTime());
    System.out.println(now_calendar.getTime());

    System.out.println(now_calendar.getTimeInMillis() - game_start_calendar.getTimeInMillis() );

}

방법2

@Test
public void date() throws Exception {
 
    Calendar calendar = new GregorianCalendar();
    calendar.set(2017,0,20,13,31,0);
 
    Calendar now = Calendar.getInstance();
    System.out.println(now.getTimeInMillis());
    System.out.println( calendar.getTimeInMillis());
    System.out.println(now.getTimeInMillis() - calendar.getTimeInMillis());
 
    Calendar result = Calendar.getInstance();
    result.setTimeInMillis(now.getTimeInMillis() - calendar.getTimeInMillis());
 
    System.out.println(result.MINUTE);
 
}

요래요래 구한다.