question: public static String sign ( String signingString , PrivateKey privateKey ) throws InvalidKeyException , SignatureException { byte [ ] bytes = signingString . getBytes ( StandardCharsets . UTF_8 ) ; Signature sig ; try { sig = Signature . getInstance ( SHA256_WITH_RSA ) ; } catch ( NoSuchAlgorithmException e ) { throw new IllegalArgumentException ( "An error occurred while getting the signature algorithm" , e ) ; } sig . initSign ( privateKey ) ; sig . update ( bytes ) ; return Hex . encodeHexString ( sig . sign ( ) ) ; }
target:  Signs a string using the private key and SHA 256 with RSA signing algorithm, and returns it as a hex-encoded string.