Use HandlerList instead of HandlerCollection

[gregw]

The HandlerCollection class is both a concrete class and the base class for HandlerList and ContextHandlerCollection. Behaviours are:

• HandlerCollection has a list of handlers that are called in order regardless of errors or handled status
• HandlerList calls handlers in order until isHandled()==true or an exception
• ContextHandlerCollection attempts to map a request to a handler by contextPath and virtual host and then calls matching in order until isHandled()==true` or an exception

Originally the basic jetty.xml setup was:

Server
  +-- HandlerCollection
       +-- ContextHandlerCollection
       +-- DefaultHandler

Which with some optional modules was extended to something like:

Server
  +-- HandlerCollection
       +-- RewriteHandler
       +-- ContextHandlerCollection
       +-- RequestLogHandler
       +-- DefaultHandler

So the HandlerCollection behaviour was needed so that the request was always rewritten and always logged. The DefaultHandler does it's own isHandled()==true check so it only handles unhandled requests.

However, now in Jetty-10 the extended structure is

Server
  +-- RewriteHandler
  |   +-- HandlerCollection
  |       +-- ContextHandlerCollection
  |       +-- DefaultHandler
  +-- RequestLog

So the HandlerCollection semantic is no longer needed. This PR replaces the common usage of HandlerCollection with the more intuitive HandlerList

[gregw]

I've given this a wide review list as I want knowledge of change this spread.

[gregw]

@sbordet @joakime @janbartel nudge

[gregw]

@sbordet @joakime @janbartel nudge2

[joakime]

It looks good.

But I would have liked it if you had left some of the HandlerList.addHandler(Handler) usages in place, as that's an important API that still needs to be tested properly.

[sbordet]

LGTM, but I would like to clarify the case where there is (ServletContextHandler, DefaultHandler).
If ServletContextHandler is a terminal Handler, then there is no point in having a DefaultHandler afterwards.
If ServletContextHandler can be configured to be non-terminal, why can it be configured so at all - seems counter intuitive that it can be both.

[joakime]

Is there a filed issue for this PR?

[sbordet]

After discussion with @gregw, LGTM.