Concrete server and client, reactive request and response
implementations should not have to be accessed outside their package.
They could be seen as private to their HttpHandler adapters and
ClientHttpConnector's respectively.
The one exception, WebSocket upgrades in spring-webflux, is an internal
framework use case, accommodated via downcast + accessors in the
abstract base classes.
Prior to this commit, the `WebClient` always throws a `ClassCastException`
when an error occurs in `bodyToMono(ParameterizedTypeReference)``, and
not the expected exception, as set up by `onStatus`
Issue: SPR-16025
Extract WebClient content into a separate file that is now included
both in the WebFlux and in the Integration sections.
This allows having RestTemplate and WebClient documented in one place
under Integration while also keeping the same included in the WebFlux
section too.
Prior to this commit, asking for a `Void` type using any of the
`ClientResponse#bodyTo*` methods would immediately return an empty
`Publisher` without consuming the response body.
Not doing so can lead to HTTP connection pool inconsistencies and/or
memory leaks, since:
* a connection that still has a response body being written to it cannot
be properly recycled in the connection pool
* incoming `DataBuffer` might not be released
This commit detects when `Void` types are asked as body types and in
those cases does the following:
1. Subscribe to the response body `Publisher` to allow the connection to
be returned to the connection pool
2. `cancel()` the body `Publisher` if the response body is not empty; in
that case, we choose to close the connection vs. consume the whole
response body
Those changes imply that `ClientHttpResponse` and other related
contracts don't need a `close()` method anymore.
Issue: SPR-16018
Includes unified detection of Kotlin's optional parameters in MethodParameter.isOptional(), reduces BeanUtils.findPrimaryConstructor to Kotlin semantics (for reuse in AutowiredAnnotationBeanPostProcessor), and finally introduces a common KotlinDetector delegate with an isKotlinType(Class) check.
Issue: SPR-15877
Issue: SPR-16020