Autogenerated userid

Question

i want to create autogenerated userid
like i created password;
but problem is duplication of password is allowed so i don get much difficulty to implemement it
& now when i am trying to generate autogenerated user id constraint is it should be unique
here's code how i generate password automatically
{color:#ff0000}+public String generatePassword() { // generate a semi-random password+
Random rand = new Random(System.currentTimeMillis());
int pwlength = 5 rand.nextInt(4);{color}
+{color:#ff0000}+StringBuilder sb = new StringBuilder(); // generate ascii codes in the range of 48 - 57 (numbers), 65 - 90 (capitals) and 97 - 122 (lowercases){color}+
{color:#ff0000}+while (sb.length() < pwlength) { // 48+ 74 = 122, the maximum value allowed.{color}
+{color:#ff0000}+char chr = (char) (48 {color}+{color:#ff0000}rand.nextInt(74));{color}
+{color:#ff0000}+if ((chr >= '0' && chr <= '9') || (chr >= 'A' && chr <= 'Z') || (chr >= 'a' && chr <= 'z')) {{color}+
{color:#ff0000}+sb.append(chr);+
+}+
+}+
return sb.toString();
+}+
{color}
this code returns me one random password
now i want to generate one random userid
but it should follows following constraints::
1>it should be combination of first 3 character from username and random number of 5 digit
2> it should be unique
3> once id generated by fun. then it should check that weather this id present in db or not, if its not present then its ok; & if present generate another
4> repeate step until we didn find out any unique userid
5> example
if user name is john
then his id will start joh then 5 digit number
like joh12345 or joh00001 or joh56465 & so on...
how should i implement this??

Answer 1

While passwords should be strong and not easily guessed, I think userIDs should be easy for the end user to remember. They don't have to be strong. If an end user enters a bad userID and/or password, you produce an error message that says 'your userID and/or password is bad'. You dont say which one is bad since you will inform him if his guess of the userID is a valid customer's name.
Here are the rules I suggest for userID:
1: userID will consist of first name, period, last name. example: john.smith
2: if there is already a userID by that, include his middle inital. example: john.a.smith
3: if the userID still can't be generated because someone has the same middle inital (or he doesn't supply his middle initial), append the next unused number in a sequence to the name. Example: john.smith1, john.smith2, etc.
I also suggest you let them generate their own password. An auto generated one will be very difficult to remember and they are more likelly to write it down to remember it (which makes it unsafe). Here is my recommendations to validate they created a strong passord:
1: must be at least 8 char
2: two letters must be upper case
3: two letters must be lower case
4: two letters must be numbers
5: two letters must be any of the following special characters:
!@#$% (or specify a set of any special characters you want)
On the form, list the above rules he needs to generate a strong password and validate against it.