INT-4215: ChainFileListFilter Exit When Empty

JIRA: https://jira.spring.io/browse/INT-4215

Due to type erasure we can't create an empty generic array from an empty list.
Don't attempt to call remaining filters when the list is empty.

spring-integration-file/src/main/java/org/springframework/integration/file/filters/ChainFileListFilter.java

@@ -23,13 +23,15 @@ import org.springframework.util.Assert;
 
 /**
  * The {@link CompositeFileListFilter} extension which chains the result
- * of the previous filter to the next one.
+ * of the previous filter to the next one. If a filter in the chain returns
+ * an empty list, the remaining filters are not invoked.
+ * @param <F> The type that will be filtered.
  *
  * @author Artem Bilan
+ * @author Gary Russell
  *
  * @since 4.3.7
  *
- * @param <F> The type that will be filtered.
  */
 public class ChainFileListFilter<F> extends CompositeFileListFilter<F> {
 
@@ -38,6 +40,9 @@ public class ChainFileListFilter<F> extends CompositeFileListFilter<F> {
 		Assert.notNull(files, "'files' should not be null");
 		List<F> leftOver = Arrays.asList(files);
 		for (FileListFilter<F> fileFilter : this.fileFilters) {
+			if (leftOver.size() == 0) {
+				break;
+			}
 			@SuppressWarnings("unchecked")
 			F[] fileArray = (F[]) leftOver.toArray();
 			leftOver = fileFilter.filterFiles(fileArray);

spring-integration-file/src/test/java/org/springframework/integration/file/CompositeFileListFilterTests.java

@@ -21,6 +21,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.isA;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 import static org.mockito.hamcrest.MockitoHamcrest.argThat;
@@ -102,7 +103,7 @@ public class CompositeFileListFilterTests {
 		assertEquals(noFiles, compositeFileFilter.filterFiles(new File[] { this.fileMock }));
 
 		verify(fileFilterMock1).filterFiles(argThat(arrayWithSize(1)));
-		verify(fileFilterMock2).filterFiles(argThat(arrayWithSize(0)));
+		verify(fileFilterMock2, never()).filterFiles(isA(File[].class));
 
 		compositeFileFilter.close();
 	}

src/reference/asciidoc/file.adoc

@@ -118,6 +118,7 @@ Say we have files `a.txt`, `a.done`, and `b.txt`.
 The pattern filter only passes `a.txt` and `b.txt`, the "done" filter will see all three files and only pass `a.txt`.
 The final result of the composite filter is only `a.txt` is released.
 
+NOTE: With the `ChainFileListFilter`, if any filter in the chain returns an empty list, the remaining filters are not invoked.
 
 Starting with _version 5.0_ an `ExpressionFileListFilter` has been introduced to allow to execute SpEL expression against file as a context evaluation root object.
 For this purpose all the XML components for file handling (local and remote), alongside with an existing `filter` attribute, have been supplied with the `filter-expression` option: