INT-4216: Fix ClassCast in ChainFileListFilter

JIRA: https://jira.spring.io/browse/INT-4216

Add test for running empty array through `ChainFileListFilter`

Assure no exceptions are throw when filter input is empty.

INT-4216: Add fix for ChainFileListFilter edge case

INT-4216: Fix checkstyle error on test class

Add copyright header to test file

* Polishing for `ChainFileListFilter` JavaDocs
* Move `CompositeFileListFilterTests` and `ChainFileListFilterIntegrationTests` to the `filters` package instead of `file` core

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

@@ -16,6 +16,7 @@
 
 package org.springframework.integration.file.filters;
 
+import java.lang.reflect.Array;
 import java.util.Arrays;
 import java.util.List;
 
@@ -25,6 +26,7 @@ import org.springframework.util.Assert;
  * The {@link CompositeFileListFilter} extension which chains the result
  * 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
@@ -44,7 +46,7 @@ public class ChainFileListFilter<F> extends CompositeFileListFilter<F> {
 				break;
 			}
 			@SuppressWarnings("unchecked")
-			F[] fileArray = (F[]) leftOver.toArray();
+			F[] fileArray = leftOver.toArray((F[]) Array.newInstance(leftOver.get(0).getClass(), leftOver.size()));
 			leftOver = fileFilter.filterFiles(fileArray);
 		}
 		return leftOver;

spring-integration-file/src/test/java/org/springframework/integration/file/filters/ChainFileListFilterIntegrationTests.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.file.filters;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+
+import org.junit.Test;
+
+/**
+ * @author Aaron Grant
+ *
+ * @since 4.3.8
+ */
+public class ChainFileListFilterIntegrationTests {
+
+	private File[] noFiles = new File[0];
+
+	private File[] oneFile = new File[] { new MockOldFile("file.txt") };
+
+	@Test
+	public void singleModifiedFilterNoFiles() throws IOException {
+		try (ChainFileListFilter<File> chain = new ChainFileListFilter<>()) {
+			chain.addFilter(new LastModifiedFileListFilter());
+			List<File> result = chain.filterFiles(noFiles);
+			assertEquals(0, result.size());
+		}
+	}
+
+	@Test
+	public void singlePatternFilter() throws IOException {
+		try (ChainFileListFilter<File> chain = new ChainFileListFilter<>()) {
+			chain.addFilter(new SimplePatternFileListFilter("*.txt"));
+			List<File> result = chain.filterFiles(oneFile);
+			assertEquals(1, result.size());
+		}
+	}
+
+	@Test
+	public void singleModifiedFilter() throws IOException {
+		try (ChainFileListFilter<File> chain = new ChainFileListFilter<>()) {
+			chain.addFilter(new LastModifiedFileListFilter());
+			List<File> result = chain.filterFiles(oneFile);
+			assertEquals(1, result.size());
+		}
+	}
+
+	@Test
+	public void patternThenModifiedFilters() throws IOException {
+		try (ChainFileListFilter<File> chain = new ChainFileListFilter<>()) {
+			chain.addFilter(new SimplePatternFileListFilter("*.txt"));
+			chain.addFilter(new LastModifiedFileListFilter());
+			List<File> result = chain.filterFiles(oneFile);
+			assertEquals(1, result.size());
+		}
+	}
+
+	@Test
+	public void modifiedThenPatternFilters() throws IOException {
+		try (ChainFileListFilter<File> chain = new ChainFileListFilter<>()) {
+			chain.addFilter(new LastModifiedFileListFilter());
+			chain.addFilter(new SimplePatternFileListFilter("*.txt"));
+			List<File> result = chain.filterFiles(oneFile);
+			assertEquals(1, result.size());
+		}
+	}
+
+	private static class MockOldFile extends File {
+
+		private static final long serialVersionUID = 1L;
+
+		MockOldFile(String pathname) {
+			super(pathname);
+		}
+
+		@Override
+		public long lastModified() {
+			return 1;
+		}
+
+	}
+
+}

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

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.integration.file;
+package org.springframework.integration.file.filters;
 
 import static org.hamcrest.Matchers.arrayWithSize;
 import static org.junit.Assert.assertEquals;
@@ -33,10 +33,6 @@ import java.util.List;
 
 import org.junit.Test;
 
-import org.springframework.integration.file.filters.ChainFileListFilter;
-import org.springframework.integration.file.filters.CompositeFileListFilter;
-import org.springframework.integration.file.filters.FileListFilter;
-
 /**
  * @author Iwein Fuld
  * @author Gary Russell