5a1846cfe5
JIRA: https://jira.spring.io/browse/INT-2480 * Introduce `headers-function` option into the `aggregator` for merging and computing headers for the output message based on the completed group * Implement a `DefaultAggregateHeadersFunction` and use it in the `AbstractAggregatingMessageGroupProcessor` for default behavior with possible injection for any other implementation * Add `DelegatingMessageGroupProcessor` to wrap any other `MessageGroupProcessor` implementations with possible usage of the `headersFunction` if result is not a `Message` or `MessageBuilder` * Make `AbstractCorrelatingMessageHandler.getOutputProcessor()` as `public` rto give access to this option from the `AggregatorSpec` to be able to inject a `headersFunction` in Java DSL configuration * Add `AbstractIntegrationMessageBuilder.getHeader()` to get access to some underlying header avoiding extra `Map` in case of `getHeaders()` * Change a logic in the `AbstractMessageProducingHandler.produceOutput()` to consult a `reply` for the `replyChannel` as well `routingSlip` header if the `reply` is a `Message` or `MessageBuilder` * Introduce a `AbstractMessageProducingHandler.messageBuilderForReply()` and use it in `AbstractMessageSplitter` to avoid duplication * Validate a new functionality in tests * Fix `FileOutboundGatewayParserTests` to rely on the `TemporaryFolder` to clean up test files after using * JavaDocs for `DefaultAggregateHeadersFunction` * Some `router.adoc` polishing * Fix link to Reactor in the `router.adoc` * Add docs for new `Function<MessageGroup, Map<String, Object>>` strategy * Doc polishing.
Spring Integration 
Checking out and Building
To check out the project and build from source, do the following:
git clone git://github.com/spring-projects/spring-integration.git
cd spring-integration
./gradlew build
NOTE: While Spring Integration runs with Java SE 6 or higher, a Java 8 compiler is required to build the project.
If you encounter out of memory errors during the build, increase available heap and permgen for Gradle:
GRADLE_OPTS='-XX:MaxPermSize=1024m -Xmx1024m'
To build and install jars into your local Maven cache:
./gradlew install
To build api Javadoc (results will be in build/api):
./gradlew api
To build reference documentation (results will be in build/reference):
./gradlew reference
To build complete distribution including -dist, -docs, and -schema zip files (results will be in build/distributions)
./gradlew dist
Using Eclipse
To generate Eclipse metadata (.classpath and .project files), do the following:
./gradlew eclipse
Once complete, you may then import the projects into Eclipse as usual:
File -> Import -> Existing projects into workspace
Browse to the 'spring-integration' root directory. All projects should import free of errors.
Using IntelliJ IDEA
To generate IDEA metadata (.iml and .ipr files), do the following:
./gradlew idea
Resources
For more information, please visit the Spring Integration website at: https://projects.spring.io/spring-integration