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 "";
}