rakeshadr commented on a change in pull request #2008:
URL: https://github.com/apache/ozone/pull/2008#discussion_r591589474



##########
File path: 
hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/security/acl/OzonePrefixPath.java
##########
@@ -0,0 +1,59 @@
+/**
+ * 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.hadoop.ozone.security.acl;
+
+import org.apache.hadoop.ozone.om.helpers.OzoneFileStatus;
+
+import java.io.IOException;
+import java.util.List;
+
+public interface OzonePrefixPath {
+
+  /**
+   * Lists immediate children(files or a directories) of the given keyPrefix.
+   * It won't do recursive traversal.
+   *
+   * Assume following is the Ozone FS tree structure.
+   *
+   *                  buck-1
+   *                    |
+   *                    a
+   *                    |
+   *      -----------------------------------
+   *     |           |                       |
+   *     b1          b2                      b3
+   *   -----       --------               ----------
+   *   |    |      |    |   |             |    |     |
+   *  c1   c2     d1   d2  d3             e1   e2   e3
+   *                   |                  |
+   *               --------               |
+   *              |        |              |
+   *           d21.txt   d22.txt        e11.txt
+   *
+   * Say, KeyPrefix = "a" will return immediate children [a/b1, a/b2, a/b3].
+   * Say, KeyPrefix = "a/b2" will return children [a/b2/d1, a/b2/d2, a/b2/d3].
+   *
+   * @param volumeName volume name
+   * @param bucketName bucket name
+   * @param keyPrefix  keyPrefix name
+   * @return list of immediate files or directories under the given keyPrefix.
+   * @throws IOException
+   */
+  List<OzoneFileStatus> getChildren(String volumeName,

Review comment:
       Thanks @xiaoyuyao for the review comments. Very good point.
   
   How about to change the List to Iterator ?
   ```
   
   interface OzonePrefixPath {
   
      Iterator<? extends OzoneFileStatus> getChildren(String keyPrefix) throws 
IOException;
   
      class PathIterator implements Iterator<OzoneFileStatus> {
   
         @Override
         public boolean hasNext() {
           // batch wise fetching....constant batchSize=1000
           return false;
         }
   
         @Override
         public OzoneFileStatus next() {
           return null;
         }
       }
   
     }
   ```




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