Binary compatibility with 2.0.X

[tomaswolf]

Make the method IoHandler.event() a default method.

This restores binary and source compatibility with 2.0.X except for classes that implement the IoHandler interface and also some other interface that would have a conflicting event() method. See JLS8 13.5.6.[1] However, since the event() method refers to the new type FilterEvent, there can be no such other conflicting method in existing code that was written and compiled against 2.0.X.

[1] https://docs.oracle.com/javase/specs/jls/se8/html/jls-13.html#jls-13.5.6

[tomaswolf]

@elecharny : you might want to consider doing this on the 2.1.X branch, too.

The point is that I want over in MINA SSHD the sshd-mina transport to work with either 2.0.X or 2.2.X. Currently that is not the case because we have our own class implementing IoHandler, so there'd be problems at run-time if sshd-mina is used together with mina-core:2.2.X.

The subclass in sshd-mina doesn't implement that event() method, and unless we bump the dependency in sshd-mina to 2.2.X, we can't since there is not FilterEvent type in 2.0.X. If we bump the dependency, then sshd-mina will not work anymore with mina-code 2.0.X. But we need to maintain compatibility with 2.0.X in sshd-mina; otherwise clients would be forced to upgrade mina-core, which they might not want to--if they've been using 2.0.X and it worked fine for them, forcing them to upgrade to 2.2.X with the (potentially huge) effort to re-test and re-validate their product is no good. One application I know of that uses sshd-mina with mina-core 2.0.X is Gerrit.

[elecharny]

I see what you'd like to have, and that somehow makes sense: helping you coping with the changes, and having no impact for the 2.2.X branch.