My current solution is:
import org.apache.commons.codec.binary.Base64;
log.info("Decoding base64 format");
String response = "b3JpZ2luYWwgU3RyaW5nIGJlZm9yZSBiYXNlNjQgZW5jb2RpbmcgaW4gSmF2YQ==";
byte[] decoded_response = Base64.decodeBase64(response);
log.info(new String(decoded_response));
Which is based on the solution provided by http://javarevisited.blogspot.pt/2012/02/how-to-encode-decode-string-in-java.html .
EDIT: Check Dmitri solution for more details.
Thanks