Issue: SPR-12181

Prior to this commit, given an enum which implements some interface,
GenericConversionService would select the String -> Enum converter even
if a converter for String -> SomeInterface was registered.  This also
affected converters that were registered for String ->
SomeBaseInterface, when SomeInterface extended SomeBaseInterface.

This change modifies the behavior of the private method
getClassHierarchy() by placing Enum.class as late as possible, pretty
much the same way as Object.class is handled.

Issue: SPR-12050

After this change, java.util.Optional is supported with @RequestParam,
@RequestHeader, and @MatrixVariable arguments in Java 8. When Optional
is used the required flag is effectively ignored.

Issue: SPR-11829

Issue: SPR-11608

CollectionToCollectionConverter avoids collection copy for untyped collection when simply returning source anyway

Also uses addAll instead of iteration over untyped collection now, supporting optimized addAll in target collection type, and avoids repeated getElementTypeDescriptor calls.

Issue: SPR-11479

Issue: SPR-11369

GenericConversionService matches converters by full generic target type, allowing for the registration of multiple converters from the same source type to different collection types

Issue: SPR-11369

Issue: SPR-11259

Issue: SPR-11242

Refactor TypeDescriptor to use ResolvableType in order to retain full
generic type information, in the process fixing MultiValueMap support
in MapToMapConverter.

Issue: SPR-9499

Issue: SPR-1528

Add ByteBufferConverter that is registered by default with the
DefaultConversionService. Allows conversion from/to a ByteBuffer and
byte[] or to any type that can be converted via a byte[].

Issue: SPR-10712

Issue: SPR-10130

Update StringToEnumConverterFactory to search superclasses until
Class.isEnum() returns true. This allows conversion when the
enum class is obtained from the enum value:

    public static enum SubFoo {
        BAR { String s() { return "x"; } };
        abstract String s();
    }

    conversionService.convert("BAR", SubFoo.BAR.getClass())

This fix is particularly important when converting collections of
enums.

Issue: SPR-10329

Issue: SPR-9793

Move code from spring-build-junit into spring-core/src/test along with
several other test utility classes. This commit removes the temporary
spring-build-junit project introduced in commit
b083bbde.

Fix deprecation compiler warnings by refactoring code or applying
@SuppressWarnings("deprecation") annotations. JUnit tests of
internally deprecated classes are now themselves marked as
@Deprecated.

Numerous EasyMock deprecation warnings will remain until the
migration to mockito can be completed.

Make use of the new JUnit functionality introduced in the previous
commit to 'Assume' that perfomance- and timing-sensitive tests should
run only when TestGroup.PERFORMANCE is selected, i.e. when
-PtestGroups="performance" has been provided at the Gradle command line.

The net effect is that these tests are now ignored by default, which
will result in far fewer false-negative CI build failures due to
resource contention and other external factors that cause slowdowns.

We will set up a dedicated performance CI build to run these tests on
an isolated machine, etc.

Issue: SPR-9984

Issue: SPR-10129

Fix serialization warnings by applying @SuppressWarnings("serial")
when appropriate.

In certain cases and for unknown reasons, a correctly-placed
@SuppressWarnings("serial") annotation will fix the warning at the
javac level (i.e. the Gradle command-line), but will produce an
"unnecessary @SuppressWarnings" warning within Eclipse. In these
cases, a private static final serialVersionUID field has been added
with the default value of 1L.

Previously the algorithm used by GenericConversionService to find
converters incorrectly searched for interfaces working up from the
base class. This caused particular problems with custom List
converters as as the Collection interface would be considered before
the List interface giving CollectionToObjectConverter precedence
over the custom converter.

The updated algorithm restores the class search order to behave in the
same way as Spring 3.1.

Issue: SPR-10116
Backport-Issue: SPR-10117
Backport-Commit: aa914497

Previously the algorithm used by GenericConversionService to find
converters incorrectly searched for interfaces working up from the
base class. This caused particular problems with custom List
converters as as the Collection interface would be considered before
the List interface giving CollectionToObjectConverter precedence
over the custom converter.

The updated algorithm restores the class search order to behave in the
same way as Spring 3.1.

Issue: SPR-10116

Bypass ObjectToObject conversion when source and object types are
identical and protect against a null source object.

Prior to this commit the TypeDescriptor was used to determine if
conversion was necessary.  This caused issues when comparing a
descriptor with annotations to one without.  The updated code
now compares using TypeDescriptor.getType().

The ObjectToObject converter will now no longer attempt to convert
null source objects.

Issue: SPR-9933

Content:

 - Rename Conditional{Conversion=>Converter}
 - Add @since tags where appropriate
 - Update Apache date headers to read 2002-2012 (not just 2012)
 - Correct minor Javadoc typo

Style:

 - Polish line breaks / whitespace
 - Use wildcard static imports where appropriate

Issue: SPR-9566, SPR-9692, SPR-9928, SPR-9927

EnumToStringConverter in now conditional and only matches Enums that
do not implement interfaces that can be converted.

Issue: SPR-9692

Prior to this commit conversion between like types would often result in
a copy of the object. This can be problematic in the case of large byte
arrays and objects that do not have a default constructor.

The ConversionService SPI now includes canBypassConvert methods that can
be used to deduce when conversion is not needed. Several existing
converters have been updated to ensure they only apply when source and
target types differ.

This change introduces new methods to the ConversionService that will
break existing implementations. However, it anticipated that most users
are consuming the ConversionService interface rather then extending it.

Issue: SPR-9566

Introduce new ConditionalConversion interface that can be applied to
Converter, ConverterFactory or GenericConverter interfaces to make
them conditional. Prior to this commit the only
ConditionalGenericConverter could be conditional.

Issue: SPR-9928

Conversion to and from UUID objects is now supported by the
DefaultConversionService.

Issue: SPR-9765

default constructor (as long as a new map copy is not required).

Issue: SPR-9284

This renaming more intuitively expresses the relationship between
subprojects and the JAR artifacts they produce.

Tracking history across these renames is possible, but it requires
use of the --follow flag to `git log`, for example

    $ git log spring-aop/src/main/java/org/springframework/aop/Advisor.java

will show history up until the renaming event, where

    $ git log --follow spring-aop/src/main/java/org/springframework/aop/Advisor.java

will show history for all changes to the file, before and after the
renaming.

See http://chrisbeams.com/git-diff-across-renamed-directories