[IO-632] Add PathUtils for operations on NIO Path.

Add PathUtils.cleanDirectory(Path).

src/main/java/org/apache/commons/io/file/Counters.java

@@ -37,7 +37,7 @@ private static class AbstractPathCounters implements PathCounters {
 
         /**
          * Constructs a new instance.
-         * 
+         *
          * @param byteCounter the byte counter.
          * @param directoryCounter the directory counter.
          * @param fileCounter the file counter.

src/main/java/org/apache/commons/io/file/CountingPathVisitor.java

@@ -87,7 +87,7 @@ public String toString() {
 
     /**
      * Updates the counters for visiting the given file.
-     * 
+     *
      * @param file the visited file.
      * @param attrs the visited file attributes.
      */

src/main/java/org/apache/commons/io/file/PathUtils.java

@@ -35,6 +35,17 @@
  */
 public final class PathUtils {
 
+    /**
+     * Cleans a directory including sub-directories without deleting directories.
+     *
+     * @param directory directory to clean.
+     * @return The visitor used to clean the given directory.
+     * @throws IOException if an I/O error is thrown by a visitor method.
+     */
+    public static PathCounters cleanDirectory(final Path directory) throws IOException {
+        return visitFileTree(CleaningPathVisitor.withLongCounters(), directory).getPathCounters();
+    }
+
     /**
      * Counts aspects of a directory including sub-directories.
      *
@@ -74,7 +85,7 @@ public static PathCounters delete(final Path path) throws IOException {
      * @throws IOException if an I/O error is thrown by a visitor method.
      */
     public static PathCounters deleteDirectory(final Path directory) throws IOException {
-        return visitFileTree(new DeletingPathVisitor(Counters.longPathCounters()), directory).getPathCounters();
+        return visitFileTree(DeletingPathVisitor.withLongCounters(), directory).getPathCounters();
     }
 
     /**
@@ -168,8 +179,8 @@ public static <T extends FileVisitor<? super Path>> T visitFileTree(final T visi
      *
      * @throws IOException if an I/O error is thrown by a visitor method
      */
-    public static <T extends FileVisitor<? super Path>> T visitFileTree(final T visitor, final String first, final String... more)
-            throws IOException {
+    public static <T extends FileVisitor<? super Path>> T visitFileTree(final T visitor, final String first,
+            final String... more) throws IOException {
         return visitFileTree(visitor, Paths.get(first, more));
     }
 

src/test/java/org/apache/commons/io/file/CleaningPathVisitorTest.java

@@ -50,6 +50,11 @@ public void afterEach() throws IOException {
         }
     }
 
+    private void applyCleanEmptyDirectory(final CleaningPathVisitor visitor) throws IOException {
+        Files.walkFileTree(tempDir, visitor);
+        assertCounts(1, 0, 0, visitor);
+    }
+
     @BeforeEach
     public void beforeEach() throws IOException {
         tempDir = Files.createTempDirectory(getClass().getCanonicalName());
@@ -64,11 +69,6 @@ public void testCleanEmptyDirectory(final CleaningPathVisitor visitor) throws IO
         applyCleanEmptyDirectory(visitor);
     }
 
-    private void applyCleanEmptyDirectory(final CleaningPathVisitor visitor) throws IOException {
-        Files.walkFileTree(tempDir, visitor);
-        assertCounts(1, 0, 0, visitor);
-    }
-
     /**
      * Tests an empty folder.
      */

src/test/java/org/apache/commons/io/file/DeletingPathVisitorTest.java

@@ -47,6 +47,11 @@ public void afterEach() throws IOException {
         }
     }
 
+    private void applyDeleteEmptyDirectory(final DeletingPathVisitor visitor) throws IOException {
+        Files.walkFileTree(tempDir, visitor);
+        assertCounts(1, 0, 0, visitor);
+    }
+
     @BeforeEach
     public void beforeEach() throws IOException {
         tempDir = Files.createTempDirectory(getClass().getCanonicalName());
@@ -63,11 +68,6 @@ public void testDeleteEmptyDirectory(final DeletingPathVisitor visitor) throws I
         Files.deleteIfExists(tempDir);
     }
 
-    private void applyDeleteEmptyDirectory(final DeletingPathVisitor visitor) throws IOException {
-        Files.walkFileTree(tempDir, visitor);
-        assertCounts(1, 0, 0, visitor);
-    }
-
     /**
      * Tests an empty folder.
      */

src/test/java/org/apache/commons/io/file/PathUtilsCleanDirectoryTest.java

@@ -0,0 +1,92 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.commons.io.file;
+
+import static org.apache.commons.io.file.CounterAssertions.assertCounts;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests {@link DeletingPathVisitor}.
+ */
+public class PathUtilsCleanDirectoryTest {
+
+    private Path tempDir;
+
+    @AfterEach
+    public void afterEach() throws IOException {
+        // temp dir should still exist since we are cleaning and not deleting.
+        assertTrue(Files.exists(tempDir));
+        // backstop
+        if (Files.exists(tempDir) && PathUtils.isEmptyDirectory(tempDir)) {
+            Files.deleteIfExists(tempDir);
+        }
+    }
+
+    @BeforeEach
+    public void beforeEach() throws IOException {
+        tempDir = Files.createTempDirectory(getClass().getCanonicalName());
+    }
+
+    /**
+     * Tests a directory with one file of size 0.
+     */
+    @Test
+    public void testCleanDirectory1FileSize0() throws IOException {
+        FileUtils.copyDirectory(Paths.get("src/test/resources/org/apache/commons/io/dirs-1-file-size-0").toFile(),
+                tempDir.toFile());
+        assertCounts(1, 1, 0, PathUtils.cleanDirectory(tempDir));
+    }
+
+    /**
+     * Tests a directory with one file of size 1.
+     */
+    @Test
+    public void testCleanDirectory1FileSize1() throws IOException {
+        FileUtils.copyDirectory(Paths.get("src/test/resources/org/apache/commons/io/dirs-1-file-size-1").toFile(),
+                tempDir.toFile());
+        assertCounts(1, 1, 1, PathUtils.cleanDirectory(tempDir));
+    }
+
+    /**
+     * Tests a directory with two subdirectorys, each containing one file of size 1.
+     */
+    @Test
+    public void testCleanDirectory2FileSize2() throws IOException {
+        FileUtils.copyDirectory(Paths.get("src/test/resources/org/apache/commons/io/dirs-2-file-size-2").toFile(),
+                tempDir.toFile());
+        assertCounts(3, 2, 2, PathUtils.cleanDirectory(tempDir));
+    }
+
+    /**
+     * Tests an empty folder.
+     */
+    @Test
+    public void testCleanEmptyDirectory() throws IOException {
+        assertCounts(1, 0, 0, PathUtils.cleanDirectory(tempDir));
+    }
+}

src/test/java/org/apache/commons/io/file/TestArguments.java

@@ -23,11 +23,11 @@
 
 class TestArguments {
 
-    static Stream<Arguments> numberCounters() {
+    static Stream<Arguments> cleaningPathVisitors() {
         // @formatter:off
         return Stream.of(
-          Arguments.of(Counters.longCounter()),
-          Arguments.of(Counters.bigIntegerCounter()));
+          Arguments.of(CleaningPathVisitor.withBigIntegerCounters()),
+          Arguments.of(CleaningPathVisitor.withLongCounters()));
         // @formatter:on
     }
 
@@ -39,19 +39,19 @@ static Stream<Arguments> countingPathVisitors() {
         // @formatter:on
     }
 
-    static Stream<Arguments> cleaningPathVisitors() {
+    static Stream<Arguments> deletingPathVisitors() {
         // @formatter:off
         return Stream.of(
-          Arguments.of(CleaningPathVisitor.withBigIntegerCounters()),
-          Arguments.of(CleaningPathVisitor.withLongCounters()));
+          Arguments.of(DeletingPathVisitor.withBigIntegerCounters()),
+          Arguments.of(DeletingPathVisitor.withLongCounters()));
         // @formatter:on
     }
 
-    static Stream<Arguments> deletingPathVisitors() {
+    static Stream<Arguments> numberCounters() {
         // @formatter:off
         return Stream.of(
-          Arguments.of(DeletingPathVisitor.withBigIntegerCounters()),
-          Arguments.of(DeletingPathVisitor.withLongCounters()));
+          Arguments.of(Counters.longCounter()),
+          Arguments.of(Counters.bigIntegerCounter()));
         // @formatter:on
     }