正则表达式判断字符串时间格式

/**
	 * 判断时间格式
	 * @param date
	 * @return
	 */
	public static String getDatetimeFormat(String date){
		date=date.trim();
		String a1 = "[0-9]{4}[0-9]{2}[0-9]{2}[0-9]{2}[0-9]{2}[0-9]{2}";//yyyyMMddHHmmss
		String a2 = "[0-9]{4}[0-9]{2}[0-9]{2}";//yyyyMMdd
		String a3 = "[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2}";//yyyy-MM-dd HH:mm:ss
		String a4 = "[0-9]{4}-[0-9]{2}-[0-9]{2}";//yyyy-MM-dd
		String a5= "[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}";//yyyy-MM-dd  HH:mm
		boolean datea1 = Pattern.compile(a1).matcher(date).matches();
		if(datea1){
			return "yyyyMMddHHmmss";
		}
		boolean datea2 = Pattern.compile(a2).matcher(date).matches();
		if(datea2){
			return "yyyyMMdd";
		}
		boolean datea3 = Pattern.compile(a3).matcher(date).matches();
		if(datea3){
			return "yyyy-MM-dd HH:mm:ss";
		}
		boolean datea4 = Pattern.compile(a4).matcher(date).matches();
		if(datea4){
			return "yyyy-MM-dd";
		}
		boolean datea5 = Pattern.compile(a5).matcher(date).matches();
		if(datea5){
			return "yyyy-MM-dd HH:mm";
		}
		return "";
	}