Not sure what you're talking about. UTF-8 is a variable-width (multi-byte-if-needed) encoding that can encode the full unicode character set, so why should there be encoding errors, or an UnmappableCharacterException? An UnmappableCharacterException is thrown if a certain character can't be represented in the specified target encoding, but as all unicode characters can be encoded in UTF-8, this exception cannot occur.
UnmappableCharacterExceptions may happen if you try to encode unicode data to Latin-1, for example, but not with UTF-8.
