[Netty 5] Lambda-friendly future listeners

[Bennett-Lynch]

Java 8, which introduced lambdas, allows for the following code:

channel.writeAndFlush(msg).addListener(new ChannelFutureListener() {
    @Override
    public void operationComplete(ChannelFuture future) {
        ...
    }
});

to become:

channel.writeAndFlush(msg).addListener((ChannelFutureListener) future -> {
    ...
});

However, this requires adding a type declaration to the lambda parameter, e.g., (ChannelFutureListener).

Given the prominence of ChannelFutureListener, would it be worth adding a method signature to ChannelFuture that explicitly supports ChannelFutureListener?

Perhaps it would actually be worth renaming the current addListener in the Future interface to addGenericListener and then introducing type-explicit methods in extensions of Future.

E.g., the ChannelFuture interface would add:

ChannelFuture addListener(ChannelFutureListener listener);

Resulting in the slightly less verbose:

channel.writeAndFlush(msg).addListener(future -> {
    ...
});

[normanmaurer]

@Bennett-Lynch yeah... That said I think we may want to cleanup all of this a bit for Netty 5. See https://github.com/netty/netty/milestone/195

[Bennett-Lynch]

Thanks, @normanmaurer.

If I can sneak one more feature request in here, I'd also like to see onSuccess() and onFailure() convenience listeners added. E.g.,

ctx.write(msg).addListener((ChannelFutureListener) future -> {
    if (future.isSuccess()) {
        ...
    }
});

would become:

ctx.write(msg).onSuccess((ChannelFutureListener) future -> {
    ...
});

And ChannelFutureListener.CLOSE_ON_FAILURE could be deprecated in favor of:

ctx.write(msg).onFailure(ChannelFutureListener.CLOSE);