Here you can find the source of getDay(String aDate)
public static int getDay(String aDate)
//package com.java2s; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.GregorianCalendar; public class Main { public static int getDay(String aDate) { int myDay = -1; if (isValidObjectModelDate(aDate)) { Integer Day = new Integer(aDate.substring(8)); myDay = Day.intValue();/* w w w . jav a2s . co m*/ } return myDay; } /** * * @param aDate * @return * */ /*==============================================================*/ public static boolean isValidObjectModelDate(String aDate) { if (aDate == null) { return true; } if (aDate.equals("")) { return true; } SimpleDateFormat myFormatter = new SimpleDateFormat("yyyy-MM-dd"); if (aDate.length() != 10) { return false; } if (!(aDate.substring(4, 5).equals("-")) || !(aDate.substring(7, 8).equals("-"))) { return false; } try { Date myDate = myFormatter.parse(aDate); } catch (ParseException myParseException) { return false; } //YYYY-MM-DD //0123456789 String year = aDate.substring(0, 4); Integer Year = new Integer(year); int myYear = Year.intValue(); String month = aDate.substring(5, 7); Integer Month = new Integer(month); int myMonth = Month.intValue(); String day = aDate.substring(8); Integer Day = new Integer(day); int myDay = Day.intValue(); if (isValidObjectModelYear(myYear)) { if (isValidObjectModelMonth(myMonth)) { if (isValidObjectModelDay(myYear, myMonth, myDay)) { return true; } else { return false; } } else { return false; } } else { return false; } } /** * * @param aYear * @return boolean * */ /*==============================================================*/ public static boolean isValidObjectModelYear(int aYear) { boolean validYear = false; if (aYear > 1800) { validYear = true; } return validYear; } /** * * @param aMonth * @return boolean * */ /*==============================================================*/ public static boolean isValidObjectModelMonth(int aMonth) { boolean result = false; if (aMonth > 0 && aMonth < 13) { result = true; } else { result = false; } return result; } /** * * @param aYear * @param aMonth * @param aDay * * @return boolean * */ /*==============================================================*/ public static boolean isValidObjectModelDay(int aYear, int aMonth, int aDay) { boolean result = false; result = isValidObjectModelYear(aYear); if (!result) { return result; } result = isValidObjectModelMonth(aMonth); if (!result) { return result; } //If they day is 0 or negative then it is an invalid date if (aDay <= 0) { return false; } switch (aMonth) { case 4: case 6: case 9: case 11: if (aDay > 30) { result = false; } else { result = true; } break; case 1: case 3: case 5: case 7: case 8: case 10: case 12: if (aDay > 31) { result = false; } else { result = true; } break; case 2: GregorianCalendar gc = new GregorianCalendar(); if (gc.isLeapYear(aYear)) { if (aDay > 29) { result = false; } else { result = true; } } else { if (aDay > 28) { result = false; } else { result = true; } } break; default: result = false; } return result; } }