Java PBKDF2 With Hmac SHA512 high concurrent issue
<pre><code>        SecretKeyFactory kf = SecretKeyFactory.getInstance(PBKDF2WithHmacSHA512);
        PBEKeySpec ks = new PBEKeySpec(password.toCharArray(), salt, count, keylen);
        SecretKey pbeKey = kf.generateSecret(ks);
        System.out.println(new BASE64Encoder().encode(pbeKey.getEncoded()));
</code></pre>

<p>Hello everyone, 
      I just use above code to generate encrypted key. But I found an urgent issue.  When I do a 30k high concurrent test, I find sometimes I will get some "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=" key. I think this should not be happened.
Do you guys have any suggestion? thanks a lot!</p>