On Sat, 10 Jul 2010 08:15:52 -0700, markspace wrote:
Robert Klemme wrote:
This is even better because you don't even need a cast:
final Class<? extends Authenticator> cl =
Class.forName(className).asSubclass(Authenticator.class);
Interesting. Although "asSubclass(Class<?>)" is a cast and the
documentation even says "Casts this Class object to represent a subclass
of...." It will throw ClassCastException if the named class is not a
type of Authenticator, which should be caught, imo, because you probably
want to provide a better error mechanism that just halting.
Definitely more than one way to do it, I agree.
No, but that solution definitely looks interesting and tidy. I wasn't
aware of the asSubclass() refinement, that's useful.
The solution I've ended up with is as follows:
1 String authClassName = config
2 .getValueAsString( AUTHENTICATORCLASSMAGICTOKEN);
3
4 if (authClassName != null) {
5 try {
6 this.authenticator = Class.forName( authClassName).asSubclass(
7 Authenticator.class).newInstance();
8 } catch (ClassCastException cce) {
9 throw new InitialisationException(
10 "Specified class 'v' was not an authenticator".replace(
11 "v", authClassName), cce);
12 } catch (ClassNotFoundException cnfe) {
13 throw new InitialisationException(
14 "Specified class 'v' was not found".replace( "v",
15 authClassName), cnfe);
16 } catch (InstantiationException ie) {
17 throw new InitialisationException(
18 "Could not create an instance of " + authClassName, ie);
19 } catch (IllegalAccessException iae) {
20 throw new InitialisationException( "Operation not permitted",
21 iae);
22 }
23 }
24
25 authenticator.init( config);
This still makes the code quite hard to read because there are so many
different exceptions being thrown; while I agree with the general
statement that one should only seek to catch the exceptions once expects
to occur (because unexpected exceptions ought to give rise to some
further escalation) given that all I'm going to do with any of these
exceptions is log it, I can't help wishing they were all subclasses of
some common 'WhileInstantiatingClassException' superclass which I could
catch just once!
code out into a separate method - even if it's just a private one. This