比较好的日期验证方法（2012.08.02）

今天工作碰到了一个日期验证的东西，写了个方法进行日期的验证，给定的String格式为“yyyy-MM-dd”，这个可以自行更改。

public class DateTools {

public static String PATTERN_DATE_DAY = "yyyy-MM-dd";
public static String PATTERN_DATE_MONTH = "yyyy-MM";
public static String PATTERN_DATE_YEAR = "yyyy";
private static String REGEX_DAY = "^\\d{4}-\\d{1,2}-\\d{1,2}$";
private static String REGEX_MONTH = "^\\d{4}-\\d{1,2}$";
private static String REGEX_YEAR = "^\\d{4}$";

public static Calendar parseStringToDate(String startDate) {
boolean matchesYear = Pattern.matches(REGEX_YEAR, startDate);
boolean matchesMonth = Pattern.matches(REGEX_MONTH, startDate);
boolean matchesDay = Pattern.matches(REGEX_DAY, startDate);

String dateString = PATTERN_DATE_DAY;
if (matchesYear) {
dateString = PATTERN_DATE_YEAR;
} else if (matchesMonth) {
dateString = PATTERN_DATE_MONTH;
} else if (matchesDay) {
dateString = PATTERN_DATE_DAY;
}

SimpleDateFormat dateFormat = new SimpleDateFormat(dateString);
try {
Date date = dateFormat.parse(startDate);
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
if (matchesMonth) {
String month = "" + Integer.parseInt(startDate.substring(startDate.indexOf("-") + 1 ));
String mm = String.valueOf(calendar.get(Calendar.MONTH) + 1);
if (!month.equals(mm)) {
return null;
}
}
if (matchesDay) {
String year = "" + Integer.parseInt(startDate.substring(0, startDate.indexOf("-")));
String month = "" + Integer.parseInt(startDate.substring(startDate.indexOf("-") + 1, startDate.lastIndexOf("-")));
String day = "" + Integer.parseInt(startDate.substring(startDate.lastIndexOf("-") + 1));
String yy = String.valueOf(calendar.get(Calendar.YEAR));
String mm = String.valueOf(calendar.get(Calendar.MONTH) + 1);
String dd = String.valueOf(calendar.get(Calendar.DAY_OF_MONTH));
if (!year.equals(yy) || !month.equals(mm) || !day.equals(dd)) {
return null;
}
}
return calendar;
} catch (ParseException ex) {
ex.printStackTrace();
}
return null;
}

}