大小写字母,数字,特殊字符中的至少3种.8位以上,正确返回true     public static boolean rexCheckPassword(String input) {
          // 8-20 位，字母、数字、字符         String regStr = "^(?![a-zA-Z]+$)(?![A-Z0-9]+$)(?![A-Z\\W_]+$)(?![a-z0-9]+$)(?![a-z\\W_]+$)(?![0-9\\W_]+$)[a-zA-Z0-9\\W_]{8,20}$";         return input.matches(regStr);     }     @Test     public static void main(String[] args){
          System.out.println(rexCheckPassword("abcd"));         System.out.println(rexCheckPassword("abcd1234"));         System.out.println(rexCheckPassword("abcd1234#"));         System.out.println(rexCheckPassword("Abcd1234"));         System.out.println(rexCheckPassword("Abcd#$%")); }}