1. Consolidate config options for handler detection in the base class
AbstractMethodMessageHandler with sub-classes like RSocketMessageHandler
now only setting the handler predicate by default (e.g. @Controller).

2. Remove autoDetection flag in favor of just having the mutually
exclusive handler Predicate<Object> vs manually registered List<Object>.
Or if both are desired for some reason, then manually register first,
and set the predicate second.

Replace the Publisher argument in RequestSpec's
data(Publisher, Class<T>) and
data(Publisher, ParameterizedTypeReference<T>) methods with Object thus
allowing any reactive type known to the ReactiveAdapterRegistry to be
passed in directly rather than adapted to Publisher first.

See gh-23076

See gh-23159

As of 1.3.40, Kotlin now provides a kotlin-scripting-jsr223-embeddable
dependency which:
 - Fixes classloading related issues
 - Provides out of the box JSR 223 support
 - Is compatible with Spring Boot Fat Jar mechanism

This commit updates Spring Framework tests and documentation accordingly.

Closes gh-23165

* pr/23162:
  Polish FormattingConversionServiceTests

Closes gh-23162

See gh-23162

* pr/23158:
  Polish YamlProcessorTests.flattenedMapIsSameAsPropertiesButOrdered()

Closes gh-23158

See gh-23158

This commit removes the MessageHandlerAcceptor sub-class of
RSocketMessageHandler, and rather than implementing directly the
contracts for RSocket client and server acceptors, RSocketMessageHandler
now exposes clientAcceptor() and serverAcceptor() methods that return
the required adapter instances.

This provides better separation between the RSocketMessageHandler and
the RSocket adapter code, and also avoids implementing generic
interfaces like the BiFunction required for the client acceptor.

Closes gh-23153

See gh-23141

This commit introduces an overloaded jsonPath() method to specify a
target type to coerce into for MockMvcResultMatchers.

 - jsonPath(String, Matcher<T>, Class<T>)

Closes gh-23141

Closes gh-23150

Prior to this commit, RestTemplate and HttpMessageConverterExtractor did
not validate that the supplied HttpMessageConverter list contained no
null elements, which can lead to a NullPointerException when the
converters are accessed.

This commit improves the user experience by failing immediately if the
supplied HttpMessageConverter list contains a null element. This applies
to constructors for RestTemplate and HttpMessageConverterExtractor as
well as to RestTemplate#setMessageConverters().

Note, however, that RestTemplate#getMessageConverters() returns a mutable
list. Thus, if a user modifies that list so that it contains null values,
that will still lead to a NullPointerException when the converters are
accessed.

This commit also introduces noNullElements() variants for collections in
org.springframework.util.Assert.

Closes gh-23151

This commit documents which attributes in @Transactional are supported
for test-managed transactions in the Spring TestContext Framework (TCF).

Closes gh-23149

{@value ...} cannot be used outside of the current type.

Closes gh-23145

* pr/23142:
  Fix typo

Closes gh-23142

See gh-23142

This commit makes sure that in DefaultMultipartMessageReader's
DefaultFilePart, the file is not closed before all bytes are written,
by using DataBufferUtils.write (see c1b6885191d6a50347aeaa14da994f0db88f26fe).

The commit also improves on the logging of the
DefaultMultipartMessageReader.

Closes gh-23130

This commit adds two methods to DataBufferUtils:
- one that reads a Flux<DataBuffer> from a Path
- one that writes a Flux<DataBuffer> to a Path

Closes gh-23122

Closes gh-23128

Prior to this commit, if a subclass of
org.springframework.web.servlet.view.AbstractView or
org.springframework.web.reactive.result.view.AbstractUrlBasedView
configured a custom value for the requestContextAttribute, that value
was overwritten with null whenever the View was dynamically
instantiated by a UrlBasedViewResolver, and this could lead to
confusing behavior for users of the View.

This commit addresses this issue by ensuring that the
UrlBasedViewResolvers in spring-webmvc and spring-webflux do not
override the requestContextAttribute in a View if the
UrlBasedViewResolver has not been explicitly configured with a custom
requestContextAttribute value.

Closes gh-23129

Closes gh-23133

This commit declares the model method parameter as @Nullable and adds
defensive guards against a null model argument.

Closes gh-23105