Java Data Type - 如何从Date获取一个月的day值

import java.util.Calendar;
import java.util.Date;

public class Main {
  public static void main(String[] argv) {
    System.out.println(getDay(new Date()));
  }

  public static Integer getDay(Date date) {
    if (date == null)
      return 0;
    Calendar cal = Calendar.getInstance();
    cal.setTime(date);
    return cal.get(Calendar.DAY_OF_MONTH);
  }
}