Re: Understanding Exceptions
On Tue, 09 Nov 2010 19:26:29 -0800, markspace wrote in
Message-Id: <ibd3d5$9kl$1@news.eternal-september.org>:
I don't like this solution above. Why? Why inform the calling code
that you might not find the algorithm you were looking for? They did
not pass the name of the algorithm in as a parameter. There's nothing
the caller could do about it. There's a maxim, I believe, about only
throwing exceptions when the caller could take some action to rectify
the situation.
I think it depends on what scope of action the calling code can take
when the exception occurs. As this is an application specific problem,
I don't think there is a correct solution for all possibilities.
Three scenarios spring to mind:-
i) Where the alternative is also a function of MessageDigest it would be
best for the calling code to pass the digest as a parameter so that the
alternative digest can be provided if an exception is thrown.
ii) If SHA-256 is the only possible solution within MessageDigest but an
alternative can be provided by another function, then it would seem best
to hardcode the Digest and let the calling code take a secondary course
of action if an exception is thrown.
iii) It's SHA-256 or nothing. In this case, throwing an exception is
pointless as there is no alternative course of action. Better to catch
it, report the problem and stop.
So I'd write you code thusly:
private static String sha256(byte[] password, byte[] iv) {
MessageDigest md = MessageDigest.getInstance("SHA-256");
md.update(iv);
byte[] hash = md.digest(password);
return byteArrayToHexString(hash);
}
Is this even an option? Without catching or throwing the exception, I
get a compile error, regardless of whether SHA-256 is supported or not.
The only thing I might add is a log statement. Since the exception is
unchecked, no one else is likely to log it. Plus you can add some extra
information to the log, since you have a better idea than higher level
code what is going on.
This is a nice solution to my scenario(iii) above where no alternative
exists.