Reduce log level for message re: missing annotation

Previously (since Spring 3.1.1) RecursiveAnnotationAttributesVisitor
logs at level WARN when ASM parsing encounters an annotation or an (enum
used within an annotation) that cannot be classloaded. This is not
necessarily indicative of an error, e.g. JSR-305 annotations such as
@Nonnull may be used only for static analysis purposes, but because
these annotations have runtime retention, they remain present in the
bytecode. Per section 9.6.1.2 of the JLS, "An annotation that is present
in the binary may or may not be available at run-time via the reflective
libraries of the Java platform."

This commit lowers the log level of these messages from warn to debug,
but leaves at warn level other messages dealing with the ability
reflectively read enum values from within annotations.

Issue: SPR-9447
Backport-Issue: SPR-9233
Backport-Commit: f55a4a1ac5a202f00dc427ba0f94d5123ec7b2de
Introduce ConfigurableEnvironment#merge

Prior to this change, AbstractApplicationContext#setParent replaced the
child context's Environment with the parent's Environment if available.
This has the negative effect of potentially changing the type of the
child context's Environment, and in any case causes property sources
added directly against the child environment to be ignored. This
situation could easily occur if a WebApplicationContext child had a
non-web ApplicationContext set as its parent. In this case the parent
Environment type would (likely) be StandardEnvironment, while the child
Environment type would (likely) be StandardServletEnvironment. By
directly inheriting the parent environment, critical property sources
such as ServletContextPropertySource are lost entirely.

This commit introduces the concept of merging an environment through
the new ConfigurableEnvironment#merge method. Instead of replacing the
child's environment with the parent's,
AbstractApplicationContext#setParent now merges property sources as
well as active and default profile names from the parent into the
child. In this way, distinct environment objects are maintained with
specific types and property sources preserved. See #merge Javadoc for
additional details.

Issue: SPR-9446
Backport-Issue: SPR-9444, SPR-9439
Backport-Commit: 9fcfd7e827323a0a47161779ff7fcad224b473d4
Introduce ConfigurableWebEnvironment

Changes introduced in Spring 3.1 for Environment support inadvertently
established a cyclic dependency between the
org.springframework.web.context and
org.springframework.web.context.support packages, specifically through
web.context.ContextLoader's invocation of
web.context.support.WebApplicationContextUtils#initServletPropertySources.

This commit introduces ConfigurableWebEnvironment to break this cyclic
dependency. All web.context.ConfigurableWebApplicationContext types now
return web.context.ConfigurableWebEnvironment from their #getEnvironment
methods; web.context.support.StandardServletEnvironment now implements
ConfigurableWebEnvironment and makes the call to
web.context.support.WebApplicationContextUtils#initServletPropertySources
within its implementation of #initPropertySources. This means that
web.context.ContextLoader now invokes
web.context.ConfigurableWebEnvironment#initPropertySources instead of
web.context.support.WebApplicationContextUtils#initServletPropertySources
and thus the cycle is broken.

Issue: SPR-9440
Backport-Issue: SPR-9439
Backport-Commit: 2a2b6eef9107a877492e965b5e063d6f1712e7f9
Fix package cycle in @EnableSpringConfigured

@EnableSpringConfigured and its @Import'ed
SpringConfiguredConfiguration @Configuration class inadvertently
established a package cycle between beans.factory.aspectj and
context.annotation due to SpringConfiguredConfiguration's
dependency on annotations such as @Configuration, @Bean and @Role.

This commit fixes this architecture bug by moving
@EnableSpringConfigured and SpringConfiguredConfiguration from the
beans.factory.aspectj package to the context.annotation package where
they belong.

This change is assumed to be very low impact as @EnableSpringConfigured
was introduced in 3.1.0 and relocation is happening as quickly as
possible in 3.1.2. @EnableSpringConfigured is assumed to be infrequently
used at this point, and for those that are the migration path
is straightforward. When upgrading from Spring 3.1.0 or 3.1.1, update
import statements in any affected @Configuration classes to reflect the
new packaging.

Backporter's note: this change causes Bundlor warnings in
org.springframework.aspect as its manifest now "imports and exports the
package org.springframework.context.annotation". To 'solve' this
problem, `fail.on.warnings=false` has been added to build.properties.
This means that future Bundlor-based warnings may go unnoticed.

Issue: SPR-9442
Backport-Issue: SPR-9441
Backport-Commit: 5327a7a37d25b67ee2ae7d1ead2a3db6847767c0
Use transactional connection during db population

Previously, DatabasePopulatorUtils#execute looked up a Connection from
the given DataSource directly which resulted in the executed statements
not being executed against a transactional connection (if any) which in
turn resulted in the statements executed by the populator potentially
not being rolled back.

Now DataSourceUtils#getConnection is used to transparently take part in
any active transaction and #releaseConnection is used to ensure the
connection is closed if appropriate.

Issue: SPR-9465
Backport-Issue: SPR-9457
Backport-Commit: 49c9a2a9157861bad53ec47b67c8d821b0b4655a
Refactor and deprecate TransactionAspectUtils

TransactionAspectUtils contains a number of methods useful in
retrieving a bean by type+qualifier. These methods are functionally
general-purpose save for the hard coding of PlatformTransactionManager
class literals throughout.

This commit generifies these methods and moves them into
BeanFactoryUtils primarily in anticipation of their use by async method
execution interceptors and aspects when performing lookups for qualified
executor beans e.g. via @Async(qualifier).

The public API of TransactionAspectUtils remains backward compatible;
all methods within have been deprecated, and all calls to those methods
throughout the framework refactored to use the new BeanFactoryUtils
variants instead.

Issue: SPR-9443
Backport-Issue: SPR-6847
Backport-Commit: 096693c46fba6e09b346a498b7002abd4d6540a9
Polish async method execution infrastructure

In anticipation of substantive changes required to implement @Async
executor qualification, the following updates have been made to the
components and infrastructure supporting @Async functionality:

 - Fix trailing whitespace and indentation errors
 - Fix generics warnings
 - Add Javadoc where missing, update to use {@code} tags, etc.
 - Avoid NPE in AopUtils#canApply
 - Organize imports to follow conventions
 - Remove System.out.println statements from tests
 - Correct various punctuation and grammar problems

Issue: SPR-9443
Backport-Issue: SPR-6847
Backport-Commit: 3fb11870d9e9fc47651c08442ac7e85140788579
Support executor qualification with @Async#value

Prior to this change, Spring's @Async annotation support was tied to a
single AsyncTaskExecutor bean, meaning that all methods marked with
@Async were forced to use the same executor. This is an undesirable
limitation, given that certain methods may have different priorities,
etc. This leads to the need to (optionally) qualify which executor
should handle each method.

This is similar to the way that Spring's @Transactional annotation was
originally tied to a single PlatformTransactionManager, but in Spring
3.0 was enhanced to allow for a qualifier via the #value attribute, e.g.

  @Transactional(ptm1)
  public void m() { ... }

where ptm1 is either the name of a PlatformTransactionManager bean or
a qualifier value associated with a PlatformTransactionManager bean,
e.g. via the <qualifier> element in XML or the @Qualifier annotation.

This commit introduces the same approach to @Async and its relationship
to underlying executor beans. As always, the following syntax remains
supported

  @Async
  public void m() { ... }

indicating that calls to #m will be delegated to the default executor,
i.e. the executor provided to

  <task:annotation-driven executor=.../>

or the executor specified when authoring a @Configuration class that
implements AsyncConfigurer and its #getAsyncExecutor method.

However, it now also possible to qualify which executor should be used
on a method-by-method basis, e.g.

  @Async(e1)
  public void m() { ... }

indicating that calls to #m will be delegated to the executor bean
named or otherwise qualified as e1. Unlike the default executor
which is specified up front at configuration time as described above,
the e1 executor bean is looked up within the container on the first
execution of #m and then cached in association with that method for the
lifetime of the container.

Class-level use of Async#value behaves as expected, indicating that all
methods within the annotated class should be executed with the named
executor. In the case of both method- and class-level annotations, any
method-level #value overrides any class level #value.

This commit introduces the following major changes:

 - Add @Async#value attribute for executor qualification

 - Introduce AsyncExecutionAspectSupport as a common base class for
   both MethodInterceptor- and AspectJ-based async aspects. This base
   class provides common structure for specifying the default executor
   (#setExecutor) as well as logic for determining (and caching) which
   executor should execute a given method (#determineAsyncExecutor) and
   an abstract method to allow subclasses to provide specific strategies
   for executor qualification (#getExecutorQualifier).

 - Introduce AnnotationAsyncExecutionInterceptor as a specialization of
   the existing AsyncExecutionInterceptor to allow for introspection of
   the @Async annotation and its #value attribute for a given method.
   Note that this new subclass was necessary for packaging reasons -
   the original AsyncExecutionInterceptor lives in
   org.springframework.aop and therefore does not have visibility to
   the @Async annotation in org.springframework.scheduling.annotation.
   This new subclass replaces usage of AsyncExecutionInterceptor
   throughout the framework, though the latter remains usable and
   undeprecated for compatibility with any existing third-party
   extensions.

 - Add documentation to spring-task-3.2.xsd and reference manual
   explaining @Async executor qualification

 - Add tests covering all new functionality

Note that the public API of all affected components remains backward-
compatible.

Issue: SPR-9443
Backport-Issue: SPR-6847
Backport-Commit: ed0576c1811bbb3a17e2e9aed2810dc3c9097a09
Test meta-@Async executor qualification

Prove that Async#value is respected even when using @Async as a meta
annotation.

Issue: SPR-9443
Backport-Issue: SPR-6847
Backport-Commit: 37e024c6ebfdc57874e5024b3e9efa69de05fa44
Introduce BeanFactoryAnnotationUtils

Commit 3f387eb9cf710e8e902861e74f7d6c5981a0b5ea refactored and
deprecated TransactionAspectUtils, moving its #qualifiedBeanOfType
and related methods into BeanFactoryUtils. This created a package cycle
between beans.factory and beans.factory.annotation due to use of the
beans.factory.annotation.Qualifier annotation in these methods.

This commit breaks the package cycle by introducing
beans.factory.annotation.BeanFactoryAnnotationUtils and moving these
@Qualifier-related methods to it. It is intentionally similar in name
and style to the familiar BeanFactoryUtils class for purposes of
discoverability.

There are no backward-compatibilty concerns associated with this change
as the cycle was introduced, caught and now fixed before a release.

Issue: SPR-9443
Backport-Issue: SPR-6847
Backport-Commit: a4b00c732b13aa1628161cb35d49463c5c39d38c
Fix scoped-proxy memory leak w/ @Resource injection

Prior to this change, request-scoped components having
@Resource-injected dependencies caused a memory leak in
DefaultListableBeanFactory#dependenciesForBeanMap.

Consider the following example:

    @Component
    @Scope(value="request", proxyMode=ScopedProxyMode.TARGET_CLASS)
    public class MyComponent {

        @Resource
        private HttpServletRequest request;

        // ...
    }

The bean name for "MyComponent" will end up being
'scopedTarget.myComponent', which will become a key in
the #dependenciesForBeanMap structure.

On the first request, the injected HttpServletRequest bean will be a
proxy and will internally have a bean name of the form
"$Proxy10@1a3a2a52". This name will be added to the Set value associated
with the 'scopedTarget.myComponent' entry in #dependenciesForBeanMap.

On the second request, the process will repeat, but the injected
HttpServletRequest will be a different proxy instance, thus having a
different identity hex string, e.g. "$Proxy10@5eba06ff". This name will
also be added to the Set value associated with the
'scopedTarget.myComponent' entry in #dependenciesForBeanMap, and this
is the source of the leak: a new entry is added to the set on each
request but should be added only once.

This commit fixes the leak by introducing caching to
CommonAnnotationBeanPostProcessor#ResourceElement similar to that already
present in AutowiredAnnotationBeanPostProcessor#AutowiredFieldElement
and #AutowiredMethodElement. Essentially, each ResourceElement instance
now tracks whether it has been created, caches the ultimate value to be
injected and returns it eagerly if necessary. Besides solving the memory
leak, this has the side effect of avoiding unnecessary proxy creation.

This fix also explains clearly why injection into request-scoped
components using @Autowired never suffered this memory leak: because the
correct caching was already in place. Because @Resource is considerably
less-frequently used than @Autowired, and given that this particular
injection arrangement is relatively infrequent, it becomes
understandable how this bug has been present without being reported
since the introduction of @Resource support in Spring 2.5: developers
were unlikely to encounter it in the first place; and if they did, the
leak was minor enough (adding strings to a Set), that it could
potentially go unnoticed indefinitely depending on request volumes and
available memory.

Issue: SPR-9363
Backport-Issue: SPR-9176
Backport-Commit: f779c199ea272cf61781e120b1ab2efc50de0cbb
Fix regression in ClassPathResource descriptions

ClassPathResource.getDescription() now returns consistent, meaningful
results for all variants of ClassPathResource's constructors.

Issue: SPR-9415
Backport-Issue: SPR-9413
Backport-Commit: b50f6e19a6820a8e735a89dfee1a85077e804ec5
Polish

Issue: SPR-9448
Backport-Issue: SPR-6870
Backport-Commit: db1cb13448dcdc11c6ebd087d0a436614d541d90
Cache by-type lookups in DefaultListableBeanFactory

Prior to this change, by-type lookups using DLBF#getBeanNamesForType
required traversal of all bean definitions within the bean factory
in order to inspect their bean class for assignability to the target
type. These operations are comparatively expensive and when there are a
large number of beans registered within the container coupled with a
large number of by-type lookups at runtime, the performance impact can
be severe. The test introduced here demonstrates such a scenario clearly.

This performance problem is likely to manifest in large Spring-based
applications using non-singleton beans, particularly request-scoped
beans that may be created and wired many thousands of times per second.

This commit introduces a simple ConcurrentHashMap-based caching strategy
for by-type lookups; container-wide assignability checks happen only
once on the first by-type lookup and are afterwards cached by type
with the values in the map being an array of all bean names assignable
to that type. This means that at runtime when creating and autowiring
non-singleton beans, the cost of by-type lookups is reduced to that of
ConcurrentHashMap#get.

Issue: SPR-9448
Backport-Issue: SPR-6870
Backport-Commit: 4c7a1c0a5403b35dd812dae1f2a753538928bb32
Reflect 3.2=>3.1.2 backports in @since tags etc

Issue: SPR-9443, SPR-6847, SPR-9446, SPR-9444, SPR-9439, SPR-9302,
       SPR-9507, SPR-9238, SPR-9397, SPR-9406, SPR-9502