String pubKey = "<Retrieved pkcs8 public key>";

pubKey = pubKey.replaceAll("(-+BEGIN PUBLIC KEY-+\\r?\\n|-+END PUBLIC KEY-+\\r?\\n?)", "");

byte[] keyBytes = Base64.decodeBase64(pubKey);

X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes);

KeyFactory kf = KeyFactory.getInstance("RSA");

PublicKey pk = kf.generatePublic(spec);