VOTE: one line can do the trick is much better forever,
how to generate a random alpha-numeric string
Here's a simple one-liner using UUIDs as the character base and being able to specify (almost) any length. (Yes, I know that using a UUID has been suggested before.)
public static String randString(int length) {
return UUID.randomUUID().toString().replace("-", "").substring(0, Math.min(length, 32)) + (length > 32 ? randString(length - 32) : "");