add servlet support

[jiacai2050]

ref: weavejester/compojure#176

Add a new option to define servlet mapping

{:servlet-mapping {"/hello" (HelloServlet.)}}

[weavejester]

I think this would be better tested in a third-party library first.

[jiacai2050]

This adapter has been used for almost two years in my company, it use the same tricks:

If requests are not matched against servlet contexts, they are passed to the original handler.

[weavejester]

What's your reasoning for including this change in the Ring Jetty adapter itself if there is a third-party adapter already available? Do you believe it's a common enough use-case to include an option for?

Have you considered other solutions, such as converting a Java servlet into a Ring handler?

[jiacai2050]

Well, the adapter I referred is mainly to be used with hystrix, what if you have another servlet? Maybe write another adapter. And I have done this when using druid's StatViewServlet.

Converting a Java servlet into a Ring handler is indeed another solution, and I have done this several times when port a Java web application into a Ring-based one. I'm not sure if sevlet-mapping integration is common for others, I just want this feature now and then.
I hope Ring can support servlet out of box, no more no less.

[weavejester]

Could this be achieved instead with the existing :configurator option? Or a function that converts a servlet into a handler function?

[jiacai2050]

configurator option doesn't work for this. Since the adapter has already defined a handler, if set to another, then the original one will be lost.

I can't image what a general function converting servlet into a handler look like, after all it's servlet that does the real business, turning a request map to a HttpServletRequest is reasonable, but not otherwise.

[weavejester]

One possibility is that we provide an option to allow the adapter to include the servlet keys that are already added when a handler is compiled into a servlet. Given this, converting a servlet into a handler becomes more straightforward.

I'm leery about adding a :servlet-mapping key to the adapter, as it provides a "back door" that exists outside the adapter specification. I'd prefer to have this tested in a third-party adapter first - one more general purpose than ring-jetty-hystrix-adapter - than add this as an option to Ring's official adapter without fully thinking through the consequences.

[jiacai2050]

OK, I get your point.
I'm fine with the solution. I will contribute another adapter based on my code, and let the time tell.
Thanks for the hard work you have done with Ring.

[jiacai2050]

Done. https://github.com/jiacai2050/ring-jetty-servlet-adapter