不重复的数字加字母。不可以有1，l，o，0

main(){    puDhm();}       //判断六位数是否重复，如果重复重新生成           public String puDhm(){               String dhm = puDhm1();               SuRedNewPacket redNewPacket = redNewPacketService.selectDhm(dhm);//兑换码去重               if(redNewPacket != null){                  return puDhm();                }else{                   return dhm;               }           }           //生成六位数           public static String puDhm1(){               String dhm = "";               for(int a=0;a<6;a++){                   dhm += returnDhm1();               }               return dhm;           }         //此如果带有一下字母或数字那么重新生成           public  static String returnDhm1(){               String val = returnDhm();                if(val.contains("o") || val.contains("l") || val.contains("0") || val.contains("1")){                   return returnDhm1();               }else{                   return val;               }          }          //生成一个数字   或字母        public static String returnDhm(){              String val = "";                Random random = new Random();                      String charOrNum = random.nextInt(2) % 2 == 0 ? "char" : "num";                //输出字母还是数字                if( "char".equalsIgnoreCase(charOrNum) ) {                    //输出是大写字母还是小写字母                    int temp = 97;//小写字母                  val = (char)(random.nextInt(26) + temp)+"";                } else if( "num".equalsIgnoreCase(charOrNum) ) {                    val = String.valueOf(random.nextInt(10));                }                return val;          }