How to generate a secure random alphanumeric string in Java efficiently?

Question

How do you generate a secure random (or pseudo-random) alphanumeric string in Java efficiently?

Answer 1

Generate a public key for an open-key encryption algorithm and convert the byte sequence to string via Base64 algorithm.

Answer 2

If you use Apache Commons Lang, the easiest way is

RandomStringUtils.random(20, 0, 0, true, true, null, new SecureRandom());

Answer 3

http://download.oracle.com/javase/6/docs/api/java/security/SecureRandom.html

From the Javadoc:

SecureRandom random = new SecureRandom();
byte bytes[] = new byte[20];
random.nextBytes(bytes);