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


 PemReader pemReader = new PemReader(new InputStreamReader(new
 FileInputStream(filename)));
 PemObject pemObject = pemReader.readPemObject();

 byte[] content = pemObject.getContent();
 X509EncodedKeySpec pubKeySpec = new X509EncodedKeySpec(content);
 RSAPublicKey publicKey =  factory.generatePublic(pubKeySpec);