The XDH KeyFactory now accepts and returns the JDK's own java.security.spec.XECPublicKeySpec and XECPrivateKeySpec on JDK 11 and later, through the jdk1.11 XDHKeys twin that already produces the XEC-implementing key classes, so an X25519 or X448 key round-trips through the standard spec as an Edwards key has done since the JDK 15 EdEC specs, with the u-coordinate reduced modulo the field prime and encoded little-endian by the conversion an incoming XECPublicKey already went through, RFC 7748 sec. 5 requiring a value at or past the prime to be taken as though it had been reduced.