Issue: SPR-16420

Issue: SPR-14753
Issue: SPR-15801

Issue: SPR-15986

Issue: SPR-15455

Issue: SPR-16188

Issue: SPR-16416

Ensure that the method returns the correct number of bytes that can be
read without blocking

Issue: #SPR-16416

Issue: SPR-16415

Issue: SPR-16409

The resolved URI instance is also being cached now. This should not make a difference in a real Servlet environment but does affect tests which assumed they could modify an HttpServletRequest path behind a pre-created ServletServerHttpRequest instance. Our WebSocket test base class has been revised accordingly, re-creating the ServletServerHttpRequest in such a case.

Issue: SPR-16414

* pr/1650:
  Polish "Remove an unnecessary intermediate variable"
  Remove an unnecessary intermediate variable

Closes gh-1650

See gh-1650

Issue: SPR-16053

Issue: SPR-16203

Issue: SPR-16385

Issue: SPR-16407

Issue: SPR-16365

Issue: SPR-16210

This commit makes sure there is no custom Content-Disposition header
before setting one automatically.

This commit also adds a headers(Consumer<HttpHeaders>) method, so that
one can user the nicer methods of HttpHeaders, as opposed to basic
strings.

Issue: SPR-16376

Issue: SPR-16267

Issue: SPR-16404

Since Java7 HttpURLConnection offers setFixedLengthStreamingMode method with long parameter which should be prefered over version with int argument, therefore casting ContentLength to int is no longer needed. Moreover it makes impossible to stream payload larger than Integer.MAX_VALUE