Prior to this commit, configuring a custom handshakeHandler when setting
up a stomp-endpoint with SockJS would not be taken into account:

  <websocket:stomp-endpoint path="/foo">
    <websocket:handshake-handler ref="customHandler"/>
    <websocket:sockjs/>
  </websocket:stomp-endpoint>

This commit fixes this by creating and registering a
WebsocketTransportHandler (with this handshakeHandler) as a
transportHandler override for the SockJSService.

Issue: SPR-11568

Issue: SPR-11586

When no @Payload is provided, it is equivalent to @Payload with default
attribute values. Since the default value of required=true, then
an argument that's not annotated is required.

A payload that is required will now throw an appropriate exception
regardless of if a conversion is required or not.

isEmptyPayload now takes the payload instead of the message
so that both the original payload and the converted payload, if
necessary, share the same logic.

JSR-303 validation is now consistently applied.

Issue: SPR-11577

Prior to this commit, the codebase was using a mix of log4j.xml
and log4j.properties for test-related logging configuration. This
can be an issue as log4j takes the xml variant first when looking
for a default bootstrap configuration.

In practice, some modules declaring the properties variant were
taking the xml variant configuration from another module.

The general structure of the configuration has also been
harmonized to provide a standard console output as well as an
easy way to enable trace logs for the current module.

The clientInboundChannel and clientOutboundChannel now use twice
the number of available processors by default to accomodate for some
degree of blocking in task execution on average.

In practice these settings still need to be configured explicitly in
applications but these should serve as better default values than
the default values in ThreadPoolTaskExecutor.

Issue: SPR-11450

Issue: SPR-11239

Prior to this commit, Spring supported meta-annotation attribute
overrides in custom composed annotations with reflection-based
annotation processing but not with ASM-based annotation processing.

This commit ensures that meta-annotation attribute overrides are
supported in AnnotationMetadataReadingVisitor.getAnnotationAttributes().

Issue: SPR-11574

This change exposes the WebSocketSession attributes through a message header.
The StompSubProtocolHandler adds this to incoming messages.
For now messaging handling  methods can access the map via @Header, e.g.:

@Header(StompHeaderAccessor.SESSION_ATTRIBUTES) Map<String, Object> attrs) {

Issue: SPR-11566

Issue: SPR-11566

Issue: SPR-11580

This commit sets the DB_CLOSE_ON_EXIT flag to false for embedded H2
databases loaded using H2EmbeddedDatabaseConfigurer (i.e., via Spring's
<jdbc:embedded-database /> XML namespace, EmbeddedDatabaseBuilder,
EmbeddedDatabaseFactory, and EmbeddedDatabaseFactoryBean).

Issue: SPR-11573

This commit improves the configurability of EmbeddedDatabaseBuilder by
exposing the following new configuration methods.

 - setDataSourceFactory(DataSourceFactory)
 - addScripts(String...)
 - setScriptEncoding(String)
 - setSeparator(String)
 - setCommentPrefix(String)
 - setBlockCommentStartDelimiter(String)
 - setBlockCommentEndDelimiter(String)
 - continueOnError(boolean)
 - ignoreFailedDrops(boolean)

If more fine grained control over the configuration of the embedded
database is required, users are recommended to use
EmbeddedDatabaseFactory with a ResourceDatabasePopulator and forego use
of the builder.

Issue: SPR-11410

Issue: SPR-11570

Issue: SPR-11574

Prior to this commit, AnnotationAttributesReadingVisitor treated Class
annotation attributes as Strings instead of Classes. As a result,
look-ups for Class attributes in meta-annotations failed with an
IllegalArgumentException.

This commit fixes this issue by consistently treating Class attributes
as Classes in AnnotationAttributesReadingVisitor.

Issue: SPR-11557

A temporary measure related to intermittent CI build server failures.

In Tiles v3 integration, underscores in filenames are
intended to identify the definition locale. This behavior
is now documented in order to avoid unexpected results
with filenames like tiles_definitions.xml.

This commit also updates Tiles v2 references to Tiles v3
in the Spring reference documentation.

Issue: SPR-11491

This commit updates reference documentation in order
to specify that ServletServerContainerFactoryBean is for
server side use and WebSocketContainerFactoryBean
for client side use.

Issue: SPR-11565

Use a custom ConfigReader to enforce the use of SynchronousDispatcher
and no other dispatchers otherwise created by default. Avoids the
creation thread pools never to be used.

Issue: SPR-11567

Ignore DISCONNECT messages if already disconnected. This can occur if
the client explicitly sends a DISCONNECT frame and then closes the
socket quickly. The closing of the WebSocket sessions also sends a
DISCONNECT upstream to ensure the broker is aware.

In ScriptUtils and related classes, SQLExceptions are now caught and
wrapped in ScriptExceptions wherever feasible.

Affected "throws" declarations have also been revised as appropriate.

Issue: SPR-11564

Extracted simple MethodInvokingBean as alternative to (and base class for) MethodInvokingFactoryBean

Issue: SPR-11196

Includes javadoc revision covering all supported EntityManager types as of JPA 2.1.

Issue: SPR-11451

This commit continues the work began in SPR-9531 as follows.

 - ScriptException now extends DataAccessException.

 - DatabasePopulator.populate() now explicitly throws ScriptException.

 - Introduced UncategorizedScriptException.

 - DatabasePopulatorUtils.execute() now throws an
   UncategorizedScriptException instead of a
   DataAccessResourceFailureException.

Issue: SPR-11564

Even though Netty is a required dependency of reactor-tcp at present,
there is no hard dependency in the spring-messaging Reactor-based
implementation.

Configure explicitly use of SynchronousDispatcher instead of the one
used otherwise by default (RingBufferDispatcher). As a result TCP
optations are now scoped to Netty's threads.

Remove Environment field. It is no longer required to shut it down
since we're now using SynchronousDispatcher by default.

Replace connection.in() with connection.consume() when composing
connection handling. The former creates a Stream for further composing,
e.g. via map(), filter() but all we need is to read a message.

Provide additional constructor that aceepts a pre-configured Reactor
TcpClient instance.

Issue: SPR-11531

Add accessor for brokerAvailable in AbstractBrokerMessageHandler
Ensure brokerAvailable is set even if eventPublisher is not
Add tests BrokerMessageHandlerTests

Turn off brokerAvailable when StompBrokerRelayMessageHandler stops
Actually stop message handling when brokerAvailable=false
Improve log messages

Issue: SPR-11563