[IO-631] Add a CountingFileVisitor (as the basis for a forthcoming

DeletingFileVisitor).

Author: Gary Gregory

src/changes/changes.xml

@@ -143,6 +143,9 @@ The <action> type attribute can be add,update,fix,remove.
       <action issue="IO-630" dev="ggregory" type="update" due-to="Gary Gregory">
         Deprecate org.apache.commons.io.output.NullOutputStream.NullOutputStream() in favor of org.apache.commons.io.output.NullOutputStream.NULL_OUTPUT_STREAM.
       </action>
+      <action issue="IO-631" dev="ggregory" type="add" due-to="Gary Gregory">
+        Add a CountingFileVisitor (as the basis for a forthcoming DeletingFileVisitor).
+      </action>
     </release>
 
     <release version="2.6" date="2017-10-15" description="Java 7 required, Java 9 supported.">

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

@@ -0,0 +1,85 @@
+/*
+ * 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 java.io.IOException;
+import java.nio.file.FileVisitResult;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * Counts files, directories, and sizes, as a visit proceeds.
+ */
+public class CountingFileVisitor extends SimpleFileVisitor<Path> {
+
+    private final AtomicLong byteCount = new AtomicLong();
+    private final AtomicLong directoryCount = new AtomicLong();
+    private final AtomicLong fileCount = new AtomicLong();
+
+    /**
+     * Gets the byte count of visited files.
+     * 
+     * @return the byte count of visited files.
+     */
+    public long getByteCount() {
+        return this.byteCount.get();
+    }
+
+    /**
+     * Gets the count of visited directories.
+     * 
+     * @return the count of visited directories.
+     */
+    public long getDirectoryCount() {
+        return this.directoryCount.get();
+    }
+
+    /**
+     * Gets the count of visited files.
+     * 
+     * @return the byte count of visited files.
+     */
+    public long getFileCount() {
+        return this.fileCount.get();
+    }
+
+    @Override
+    public FileVisitResult postVisitDirectory(final Path dir, final IOException exc) throws IOException {
+        directoryCount.incrementAndGet();
+        return FileVisitResult.CONTINUE;
+    }
+
+    @Override
+    public String toString() {
+        return String.format("%,d files in %,d directories for %,d bytes", Long.valueOf(fileCount.longValue()),
+                Long.valueOf(directoryCount.longValue()), Long.valueOf(byteCount.longValue()));
+    }
+
+    @Override
+    public FileVisitResult visitFile(final Path file, final BasicFileAttributes attrs) throws IOException {
+        if (Files.exists(file)) {
+            fileCount.incrementAndGet();
+            byteCount.addAndGet(attrs.size());
+        }
+        return FileVisitResult.CONTINUE;
+    }
+
+}

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

@@ -0,0 +1,85 @@
+/*
+ * 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 java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests {@link CountingFileVisitor}.
+ */
+public class CountingFileVisitorTest {
+
+    /**
+     * Tests an empty folder.
+     */
+    @Test
+    public void testEmptyFolder() throws IOException {
+        final Path tempDirectory = Files.createTempDirectory(getClass().getCanonicalName());
+        try {
+            final CountingFileVisitor visitor = new CountingFileVisitor();
+            Files.walkFileTree(tempDirectory, visitor);
+            Assertions.assertEquals(1, visitor.getDirectoryCount());
+            Assertions.assertEquals(0, visitor.getFileCount());
+            Assertions.assertEquals(0, visitor.getByteCount());
+        } finally {
+            Files.delete(tempDirectory);
+        }
+    }
+
+    /**
+     * Tests a directory with one file of size 0.
+     */
+    @Test
+    public void testFolders1FileSize0() throws IOException {
+        final CountingFileVisitor visitor = new CountingFileVisitor();
+        Files.walkFileTree(Paths.get("src/test/resources/org/apache/commons/io/dirs-1-file-size-0"), visitor);
+        Assertions.assertEquals(1, visitor.getDirectoryCount());
+        Assertions.assertEquals(1, visitor.getFileCount());
+        Assertions.assertEquals(0, visitor.getByteCount());
+    }
+
+    /**
+     * Tests a directory with one file of size 1.
+     */
+    @Test
+    public void testFolders1FileSize1() throws IOException {
+        final CountingFileVisitor visitor = new CountingFileVisitor();
+        Files.walkFileTree(Paths.get("src/test/resources/org/apache/commons/io/dirs-1-file-size-1"), visitor);
+        Assertions.assertEquals(1, visitor.getDirectoryCount());
+        Assertions.assertEquals(1, visitor.getFileCount());
+        Assertions.assertEquals(1, visitor.getByteCount());
+    }
+
+    /**
+     * Tests a directory with two subdirectorys, each containing one file of size 1.
+     */
+    @Test
+    public void testFolders2FileSize2() throws IOException {
+        final CountingFileVisitor visitor = new CountingFileVisitor();
+        Files.walkFileTree(Paths.get("src/test/resources/org/apache/commons/io/dirs-2-file-size-2"), visitor);
+        Assertions.assertEquals(3, visitor.getDirectoryCount());
+        Assertions.assertEquals(2, visitor.getFileCount());
+        Assertions.assertEquals(2, visitor.getByteCount());
+    }
+}

src/test/resources/org/apache/commons/io/dirs-1-file-size-0/file-size-0.bin

@@ -0,0 +1 @@
+a

src/test/resources/org/apache/commons/io/dirs-1-file-size-1/file-size-1.bin

@@ -0,0 +1 @@
+a

src/test/resources/org/apache/commons/io/dirs-2-file-size-2/dirs-a-file-size-1/file-size-1.bin

@@ -0,0 +1 @@
+a