Issue: SPR-11393

Issue: SPR-11393

Issue: SPR-11393

Issue: SPR-11393

Issue: SPR-11393

This commit introduces first-class support for aliases for annotation
attributes. Specifically, this commit introduces a new @AliasFor
annotation that can be used to declare a pair of aliased attributes
within a single annotation or an alias from an attribute in a custom
composed annotation to an attribute in a meta-annotation.

To support @AliasFor within annotation instances, AnnotationUtils has
been overhauled to "synthesize" any annotations returned by "get" and
"find" searches. A SynthesizedAnnotation is an annotation that is
wrapped in a JDK dynamic proxy which provides run-time support for
@AliasFor semantics. SynthesizedAnnotationInvocationHandler is the
actual handler behind the proxy.

In addition, the contract for @AliasFor is fully validated, and an
AnnotationConfigurationException is thrown in case invalid
configuration is detected.

For example, @ContextConfiguration from the spring-test module is now
declared as follows:

    public @interface ContextConfiguration {

        @AliasFor(attribute = "locations")
        String[] value() default {};

        @AliasFor(attribute = "value")
        String[] locations() default {};

        // ...
    }

The following annotations and their related support classes have been
modified to use @AliasFor.

- @ManagedResource
- @ContextConfiguration
- @ActiveProfiles
- @TestExecutionListeners
- @TestPropertySource
- @Sql
- @ControllerAdvice
- @RequestMapping

Similarly, support for AnnotationAttributes has been reworked to
support @AliasFor as well. This allows for fine-grained control over
exactly which attributes are overridden within an annotation hierarchy.
In fact, it is now possible to declare an alias for the 'value'
attribute of a meta-annotation.

For example, given the revised declaration of @ContextConfiguration
above, one can now develop a composed annotation with a custom
attribute override as follows.

    @ContextConfiguration
    public @interface MyTestConfig {

        @AliasFor(
           annotation = ContextConfiguration.class,
           attribute = "locations"
        )
        String[] xmlFiles();

        // ...
    }

Consequently, the following are functionally equivalent.

- @MyTestConfig(xmlFiles = "test.xml")
- @ContextConfiguration("test.xml")
- @ContextConfiguration(locations = "test.xml").

Issue: SPR-11512, SPR-11513

`BeanWrapperImpl` and `DirectFieldAccessor` are two
`ConfigurablePropertyAccessor` implementations with different features
set.

This commit harmonizes the two implementations to use a common base class
that delegates the actual property handling to the sub-classes:

* `BeanWrapperImpl`:  `PropertyDescriptor` and introspection utilities
* `DirectFieldAccessor`: reflection on `java.lang.Field`

Issues: SPR-12206 - SPR-12805

Issue: SPR-13035

Issue: SPR-12926

Remove unused imports

Issue: SPR-12893

This commit introduces support for OkHttp
(http://square.github.io/okhttp/) as a backing implementation for
ClientHttpRequestFactory and AsyncClientHttpRequestFactory.

Issue: SPR-12893

After this change CorsProcessor has a single processRequest method and
it also explicitly deals with a null CorsConfiguration, which for
pre-flight requests results in a rejection while for simple requests
results in no CORS headers added.

The AbstractHandlerMapping now uses a LinkedHashMap to preserve the
order in which global patterns are provided.

This commit adds JavaConfig based global CORS configuration
capabilities to Spring MVC. It is now possible to specify
multiple CORS configurations, each mapped on a path pattern,
by overriding
WebMvcConfigurerAdapter#configureCrossOrigin(CrossOriginConfigurer).

It is also possible to combine global and @CrossOrigin based
CORS configuration.

Issue: SPR-12933

Issue: SPR-12750, SPR-12942

This change introduces a strategy for expanding a URI template into a
URI and makes it a property of the RestTemplate and AsyncRestTemplate
so that they can be pre-configured with such a strategy.

The DefaultUriTemplateHandler relies on UriComponentsBuilder internally
and provides functionality equivalent to using the UriTemplate.
A DefaultUriTemplateHandler can also be configured to parse the path
of a URI template into path segments in order to allow expanding URI
variables according to path segment encoding rules.

Issue: SPR-12750

Issue: SPR-12750

(cherry picked from commit 9e925aa8)

(cherry picked from commit a8f75399)

Issue: SPR-11694

Issue: SPR-12983

Before this change AbstractHandlerMethodMapping used a map from Method
to CorsConfiguration. That works for regular @RequestMapping methods.
However frameworks like Spring Boot and Spring Integration may
programmatically register the same Method under multiple mappings,
i.e. adapter/gateway type classes.

This change ensures that CorsConfiguraiton is indexed by HandlerMethod
so that we can store CorsConfiguration for different handler instances
even when the method is the same.

In order for to make this work, HandlerMethod now provides an
additional field called resolvedFromHandlerMethod that returns the
original HandlerMethod (with the String bean name). This makes it
possible to  perform reliable lookups.

Issue: SPR-11541

CorsConfiguration now provides methods to check and determine the
allowed origin, method, and headers according to its own configuration.

This simplifies significantly the work that needs to be done from
DefaultCorsProcessor. However an alternative CorsProcessor can still
access the raw CorsConfiguration and perform its own checks.

Issue: SPR-12885

This commit adds CORS related headers to HttpHeaders
and update DefaultCorsProcessor implementation to
use ServerHttpRequest and ServerHttpResponse instead
of HttpServletRequest and HttpServletResponse. Usage
of ServerHttpResponse allows to avoid using Servlet 3.0
specific methods in order keep CORS support Servlet 2.5
compliant.

Issue: SPR-12885

Issue: SPR-12960

Issue: SPR-12956

Issue: SPR-12296

Issue: SPR-12597

Issue: SPR-12925