This commit updates Spring Integration to depend upon Spring 4, making
use of the message types that have moved from Spring Integration into
Spring's new spring-messaging module.
The default message converter no longer supports conversion of a
message that is null, throwing an IllegalArgumentException if an
attempt is made to convert null. Furthermore, GenericMessagingTemplate
does not support sending null, again throwing an
IllegalArgumentException. Previously, MessagingTemplate had no-oped an
attempt to send null.
ConcurrentAggregatorTests and AggregatorTests both had a single test
that was specifically testing the behaviour of an aggregator that
returns null for its message. These tests have been removed.
CorrelatingMessageHandlerTests have been updated to specify some
additional behaviour for its mocks so that null messages are not
returned.
These are the only functional changes that have been made. All other
changes are simply for moving to the repackaged and/or renamed types.
In the move to being part of core Spring, a number of constants and
header accessor methods have moved from MessageHeaders to
MessageHeaderAccessor. This commit continues this pattern for
the enterprise integration headers that are specific to Spring
Integration. A new class, EiMessageHeaderAccessor, has been created.
This class provides constants and methods for working with SI-specific
headers. The main code and tests have been updated to use this new
class.
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