JIRA: https://jira.spring.io/browse/INT-4430
When Iterator-based `FileSplitter` splits the file, and an exception
throws in downstream flow (in the same thread), the exception propagates
to the caller leaving underlying file reader opened.
This commit changes `AbstractMessageSplitter` the way, that,
when any exception happens, if Iterator implements `java.io.Closeable`,
its `close()` method will be called before propagating exception.
Also `FileSplitter`'s underlying iterator implements `Closeable` now.
* Make `CloseableIterator` to follow `Closeable` contract.
Now `CloseableIterator.close()` declares `IOException` and can be used
as base interface for `FunctionIterator`.
* Adjust tests.
Adjust tests to reflect the fact that we call `close()` on the reader
one more time in the end of iterator.
**Cherry-pick to 5.0.x and 4.3.x**
(cherry picked from commit 7f25cba)
# Conflicts:
# spring-integration-core/src/main/java/org/springframework/integration/splitter/AbstractMessageSplitter.java
# spring-integration-core/src/main/java/org/springframework/integration/util/FunctionIterator.java
# spring-integration-file/src/main/java/org/springframework/integration/file/splitter/FileSplitter.java
# spring-integration-file/src/test/java/org/springframework/integration/file/remote/StreamingInboundTests.java
# spring-integration-file/src/test/java/org/springframework/integration/file/splitter/FileSplitterTests.java
c45f9a6544