List files within directory

Issue: BAEL-2447

core-java-io/src/main/java/com/baeldung/files/ListFiles.java

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+package com.baeldung.files;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.DirectoryStream;
+import java.nio.file.FileVisitResult;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class ListFiles {
+    public static final int DEPTH = 1;
+
+    public Set<String> listFilesUsingJavaIO(String dir) {
+        return Stream.of(new File(dir).listFiles())
+            .filter(file -> !file.isDirectory())
+            .map(File::getName)
+            .collect(Collectors.toSet());
+    }
+
+    public Set<String> listFilesUsingFileWalk(String dir, int depth) throws IOException {
+        try (Stream<Path> stream = Files.walk(Paths.get(dir), depth)) {
+            return stream.filter(file -> !Files.isDirectory(file))
+                .map(Path::getFileName)
+                .map(Path::toString)
+                .collect(Collectors.toSet());
+        }
+    }
+
+    public Set<String> listFilesUsingFileWalkAndVisitor(String dir) throws IOException {
+        Set<String> fileList = new HashSet<>();
+        Files.walkFileTree(Paths.get(dir), new SimpleFileVisitor<Path>() {
+            @Override
+            public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
+                if (!Files.isDirectory(file)) {
+                    fileList.add(file.getFileName()
+                        .toString());
+                }
+                return FileVisitResult.CONTINUE;
+            }
+        });
+        return fileList;
+    }
+
+    public Set<String> listFilesUsingDirectoryStream(String dir) throws IOException {
+        Set<String> fileList = new HashSet<>();
+        try (DirectoryStream<Path> stream = Files.newDirectoryStream(Paths.get(dir))) {
+            for (Path path : stream) {
+                if (!Files.isDirectory(path)) {
+                    fileList.add(path.getFileName()
+                        .toString());
+                }
+            }
+        }
+        return fileList;
+    }
+
+}

core-java-io/src/test/java/com/baeldung/file/ListFilesUnitTest.java

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+package com.baeldung.file;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.IOException;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.junit.Test;
+
+import com.baeldung.files.ListFiles;
+
+public class ListFilesUnitTest {
+
+    private ListFiles listFiles = new ListFiles();
+    private String DIRECTORY = "src/test/resources/listFilesUnitTestFolder";
+    private static final int DEPTH = 1;
+    private Set<String> EXPECTED_FILE_LIST = new HashSet<String>() {
+        {
+            add("test.xml");
+            add("employee.json");
+            add("students.json");
+            add("country.txt");
+        }
+    };
+
+    @Test
+    public void givenDir_whenUsingJAVAIO_thenListAllFiles() throws IOException {
+        assertEquals(EXPECTED_FILE_LIST, listFiles.listFilesUsingJavaIO(DIRECTORY));
+    }
+
+    @Test
+    public void givenDir_whenWalkingTree_thenListAllFiles() throws IOException {
+        assertEquals(EXPECTED_FILE_LIST, listFiles.listFilesUsingFileWalk(DIRECTORY,DEPTH));
+    }
+
+    @Test
+    public void givenDir_whenWalkingTreeWithVisitor_thenListAllFiles() throws IOException {
+        assertEquals(EXPECTED_FILE_LIST, listFiles.listFilesUsingFileWalkAndVisitor(DIRECTORY));
+    }
+
+    @Test
+    public void givenDir_whenUsingDirectoryStream_thenListAllFiles() throws IOException {
+        assertEquals(EXPECTED_FILE_LIST, listFiles.listFilesUsingDirectoryStream(DIRECTORY));
+    }
+}

core-java-io/src/test/resources/listFilesUnitTestFolder/country.txt

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+This is a sample txt file for unit test ListFilesUnitTest

core-java-io/src/test/resources/listFilesUnitTestFolder/employee.json

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+{}

core-java-io/src/test/resources/listFilesUnitTestFolder/students.json

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+{}

core-java-io/src/test/resources/listFilesUnitTestFolder/test.xml

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+<xml></xml>