Make Server::setDefaultHandler and Server::setErrorHandler arguments consistent

[scrat98]

Jetty version(s)
12.0.16

Enhancement Description
There is an inconsistency in arguments between Server::setDefaultHandler and Server::setErrorHandler.

• Server::setDefaultHandler accepts org.eclipse.jetty.server.Handler
• Server::setErrorHandler accepts org.eclipse.jetty.server.Request.Handler

I would like to use in Application code only org.eclipse.jetty.server.Handler and if I do so and use it with Server::setErrorHandler then I'll get a warning
WARN o.e.jetty.server.Handler$Abstract - No Server set for csclhs.UnhandledErrorsHandler@5ace1ed4{STARTING} and due to this I need to implement my hanlder as a org.eclipse.jetty.server.Request.Handler to suppress this warning.

Nothing serious, but I think it should be easy to change.

[janbartel]

@scrat98 I'm not sure it's a good idea to have a single handler that performs both error handling and also last resort handling of a request. I think it makes your code more monolithic and less flexible, but, ymmv.

As a org.eclipse.jetty.server.Handler is-a org.eclipse.jetty.server.Request.Handler, then you should be ok, assuming you're using the same instance for both setDefaultHandler and setErrorHandler and you call them in that order: the server will be set on the instance by setDefaultHandler so it's ready for the call to setErrorHandler. Are you in fact using different instances? If so, I think it's indicative that you should probably split your code. If you really don't want to/can't do that, then you'll have to call setServer on the instance before you pass it into setErrorHandler.

[scrat98]

@janbartel I'm using different instances (have ErrorsHandler and DefaultHandler classes). My point was that in the application code I have plenty of handlers (20 for example) and all of them implement server.Handler.

But to avoid warn log, only single ErrorHandler implements server.Request.Handler also with a comment if someone decided to change it to server.Handler. And this inconsistency just gives my eye no rest, nothing serious.

[janbartel]

I think we will have to leave the published method signatures as they are - definitely at least for 12.0 - but maybe in setErrorHandler we could call setServer iff the handler isinstanceof org.eclipse.jetty.server.Handler. Let me take a look.