HADOOP-11421. Add IOUtils#listDirectory (cmccabe)

(cherry picked from commit 9937eef7f7)

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -74,6 +74,8 @@ Release 2.7.0 - UNRELEASED
     HADOOP-11248. Add hadoop configuration to disable Azure Filesystem metrics
     collection. (Shanyu Zhao via cnauroth)
 
+    HADOOP-11421. Add IOUtils#listDirectory (cmccabe)
+
   OPTIMIZATIONS
 
     HADOOP-11323. WritableComparator#compare keeps reference to byte array.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/IOUtils.java

@@ -23,12 +23,19 @@ import java.net.Socket;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.nio.channels.WritableByteChannel;
+import java.nio.file.DirectoryStream;
+import java.nio.file.DirectoryIteratorException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
 
 import org.apache.commons.logging.Log;
 
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.util.ChunkedArrayList;
 
 /**
  * An utility class for I/O related functionality. 
@@ -310,4 +317,33 @@ public class IOUtils {
       offset += fc.write(buf, offset);
     } while (buf.remaining() > 0);
   }
+
+  /**
+   * Return the complete list of files in a directory as strings.<p/>
+   *
+   * This is better than File#listDir because it does not ignore IOExceptions.
+   *
+   * @param dir              The directory to list.
+   * @param filter           If non-null, the filter to use when listing
+   *                         this directory.
+   * @return                 The list of files in the directory.
+   *
+   * @throws IOException     On I/O error
+   */
+  public static List<String> listDirectory(File dir, FilenameFilter filter)
+      throws IOException {
+    ArrayList<String> list = new ArrayList<String> ();
+    try (DirectoryStream<Path> stream =
+             Files.newDirectoryStream(dir.toPath())) {
+      for (Path entry: stream) {
+        String fileName = entry.getFileName().toString();
+        if ((filter == null) || filter.accept(dir, fileName)) {
+          list.add(fileName);
+        }
+      }
+    } catch (DirectoryIteratorException e) {
+      throw e.getCause();
+    }
+    return list;
+  }
 }

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/TestIOUtils.java

@@ -24,14 +24,21 @@ import static org.junit.Assert.fail;
 import java.io.ByteArrayInputStream;
 import java.io.EOFException;
 import java.io.File;
+import java.io.FilenameFilter;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.RandomAccessFile;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
+import java.nio.file.Files;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
 
+import org.apache.commons.io.FileUtils;
 import org.apache.hadoop.test.GenericTestUtils;
+import org.junit.Assert;
 import org.junit.Test;
 import org.mockito.Mockito;
 
@@ -214,4 +221,41 @@ public class TestIOUtils {
       in.close();
     }
   }
+
+  private static enum NoEntry3Filter implements FilenameFilter {
+    INSTANCE;
+
+    @Override
+    public boolean accept(File dir, String name) {
+      return !name.equals("entry3");
+    }
+  }
+
+  @Test
+  public void testListDirectory() throws IOException {
+    File dir = new File("testListDirectory");
+    Files.createDirectory(dir.toPath());
+    try {
+      Set<String> entries = new HashSet<String>();
+      entries.add("entry1");
+      entries.add("entry2");
+      entries.add("entry3");
+      for (String entry : entries) {
+        Files.createDirectory(new File(dir, entry).toPath());
+      }
+      List<String> list = IOUtils.listDirectory(dir,
+          NoEntry3Filter.INSTANCE);
+      for (String entry : list) {
+        Assert.assertTrue(entries.remove(entry));
+      }
+      Assert.assertTrue(entries.contains("entry3"));
+      list = IOUtils.listDirectory(dir, null);
+      for (String entry : list) {
+        entries.remove(entry);
+      }
+      Assert.assertTrue(entries.isEmpty());
+    } finally {
+      FileUtils.deleteDirectory(dir);
+    }
+  }
 }