计算两个日期之间的天数

public static long getDays(String from,String to,String format){
	long days=0;
	if(from==null||to==null){
		return days;
	}
	SimpleDateFormat sdf=new SimpleDateFormat(format);
	try {
		long tt=sdf.parse(to).getTime();
		long ft=sdf.parse(from).getTime();
		days=(tt-ft)/(1000 * 60 * 60 * 24);
	} catch (ParseException e) {
		e.printStackTrace();
		return days;
	}
	return days;
}