HDFS-10784. Implement WebHdfsFileSystem#listStatusIterator.

(cherry picked from commit 85bab5fb572194fda38854f1f21c670925058009)

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/JsonUtilClient.java

@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.hdfs.web;
 
+import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import org.apache.hadoop.fs.ContentSummary;
@@ -33,6 +34,7 @@
 import org.apache.hadoop.fs.permission.FsPermission;
 import org.apache.hadoop.hdfs.DFSUtilClient;
 import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.hadoop.hdfs.protocol.DirectoryListing;
 import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
 import org.apache.hadoop.hdfs.protocol.FsPermissionExtension;
 import org.apache.hadoop.hdfs.protocol.HdfsConstants;
@@ -141,6 +143,25 @@ static HdfsFileStatus toFileStatus(final Map<?, ?> json,
         storagePolicy);
   }
 
+  static DirectoryListing toDirectoryListing(final Map<?, ?> json) {
+    if (json == null) {
+      return null;
+    }
+    final List<?> list = JsonUtilClient.getList(json,
+        "partialListing");
+
+    HdfsFileStatus[] partialListing = new HdfsFileStatus[list.size()];
+    int i = 0;
+    for (Object o : list) {
+      final Map<?, ?> m = (Map<?, ?>) o;
+      partialListing[i++] = toFileStatus(m, false);
+    }
+    int remainingEntries = getInt(json, "remainingEntries", -1);
+    Preconditions.checkState(remainingEntries != -1,
+        "remainingEntries was not set");
+    return new DirectoryListing(partialListing, remainingEntries);
+  }
+
   /** Convert a Json map to an ExtendedBlock object. */
   static ExtendedBlock toExtendedBlock(final Map<?, ?> m) {
     if (m == null) {

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/WebHdfsFileSystem.java

@@ -64,6 +64,7 @@
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.GlobalStorageStatistics;
 import org.apache.hadoop.fs.GlobalStorageStatistics.StorageStatisticsProvider;
+import org.apache.hadoop.fs.RemoteIterator;
 import org.apache.hadoop.fs.StorageStatistics;
 import org.apache.hadoop.hdfs.DFSOpsCountStatistics;
 import org.apache.hadoop.hdfs.DFSOpsCountStatistics.OpType;
@@ -79,6 +80,7 @@
 import org.apache.hadoop.hdfs.DFSUtilClient;
 import org.apache.hadoop.hdfs.HAUtilClient;
 import org.apache.hadoop.hdfs.client.HdfsClientConfigKeys;
+import org.apache.hadoop.hdfs.protocol.DirectoryListing;
 import org.apache.hadoop.hdfs.protocol.HdfsConstants;
 import org.apache.hadoop.hdfs.protocol.HdfsFileStatus;
 import org.apache.hadoop.hdfs.security.token.delegation.DelegationTokenIdentifier;
@@ -106,6 +108,7 @@
 import org.slf4j.LoggerFactory;
 
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Charsets;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 
@@ -1494,6 +1497,58 @@ FileStatus[] decodeResponse(Map<?,?> json) {
     }.run();
   }
 
+  private static final byte[] EMPTY_ARRAY = new byte[] {};
+  private class DirListingIterator<T extends FileStatus> implements
+      RemoteIterator<T> {
+
+    private final Path path;
+    private DirectoryListing thisListing;
+    private int i = 0;
+    private byte[] prevKey = EMPTY_ARRAY;
+
+    DirListingIterator(Path path) {
+      this.path = path;
+    }
+
+    @Override
+    public boolean hasNext() throws IOException {
+      if (thisListing == null) {
+        fetchMore();
+      }
+      return i < thisListing.getPartialListing().length ||
+          thisListing.hasMore();
+    }
+
+    private void fetchMore() throws IOException {
+      thisListing = new FsPathResponseRunner<DirectoryListing>(
+          GetOpParam.Op.LISTSTATUS_BATCH,
+          path, new StartAfterParam(new String(prevKey, Charsets.UTF_8))) {
+        @Override
+        DirectoryListing decodeResponse(Map<?, ?> json) throws IOException {
+          return JsonUtilClient.toDirectoryListing(json);
+        }
+      }.run();
+      i = 0;
+      prevKey = thisListing.getLastName();
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public T next() throws IOException {
+      Preconditions.checkState(hasNext(), "No more items in iterator");
+      if (i == thisListing.getPartialListing().length) {
+        fetchMore();
+      }
+      return (T)makeQualified(thisListing.getPartialListing()[i++], path);
+    }
+  }
+
+  @Override
+  public RemoteIterator<FileStatus> listStatusIterator(final Path f)
+      throws FileNotFoundException, IOException {
+    return new DirListingIterator<>(f);
+  }
+
   @Override
   public Token<DelegationTokenIdentifier> getDelegationToken(
       final String renewer) throws IOException {

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/resources/GetOpParam.java

@@ -41,7 +41,8 @@ public enum Op implements HttpOpParam.Op {
 
     NULL(false, HttpURLConnection.HTTP_NOT_IMPLEMENTED),
 
-    CHECKACCESS(false, HttpURLConnection.HTTP_OK);
+    CHECKACCESS(false, HttpURLConnection.HTTP_OK),
+    LISTSTATUS_BATCH(false, HttpURLConnection.HTTP_OK);
 
     final boolean redirect;
     final int expectedHttpResponseCode;

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/resources/StartAfterParam.java

@@ -0,0 +1,38 @@
+/**
+ * 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.hdfs.web.resources;
+
+/**
+ * Used during batched ListStatus operations.
+ */
+public class StartAfterParam extends StringParam {
+
+  public static final String NAME = "startafter";
+  public static final String DEFAULT = "";
+
+  private static final Domain DOMAIN = new Domain(NAME, null);
+
+  public StartAfterParam(final String str) {
+    super(DOMAIN, str != null && !str.equals(DEFAULT) ? str : null);
+  }
+
+  @Override
+  public String getName() {
+    return NAME;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/web/resources/NamenodeWebHdfsMethods.java

@@ -779,11 +779,13 @@ public Response getRoot(
       @QueryParam(TokenServiceParam.NAME) @DefaultValue(TokenServiceParam.DEFAULT)
           final TokenServiceParam tokenService,
       @QueryParam(NoRedirectParam.NAME) @DefaultValue(NoRedirectParam.DEFAULT)
-          final NoRedirectParam noredirect
+          final NoRedirectParam noredirect,
+      @QueryParam(StartAfterParam.NAME) @DefaultValue(StartAfterParam.DEFAULT)
+          final StartAfterParam startAfter
       ) throws IOException, InterruptedException {
     return get(ugi, delegation, username, doAsUser, ROOT, op, offset, length,
         renewer, bufferSize, xattrNames, xattrEncoding, excludeDatanodes, fsAction,
-        tokenKind, tokenService, noredirect);
+        tokenKind, tokenService, noredirect, startAfter);
   }
 
   /** Handle HTTP GET request. */
@@ -822,12 +824,14 @@ public Response get(
       @QueryParam(TokenServiceParam.NAME) @DefaultValue(TokenServiceParam.DEFAULT)
           final TokenServiceParam tokenService,
       @QueryParam(NoRedirectParam.NAME) @DefaultValue(NoRedirectParam.DEFAULT)
-          final NoRedirectParam noredirect
+          final NoRedirectParam noredirect,
+      @QueryParam(StartAfterParam.NAME) @DefaultValue(StartAfterParam.DEFAULT)
+          final StartAfterParam startAfter
       ) throws IOException, InterruptedException {
 
     init(ugi, delegation, username, doAsUser, path, op, offset, length,
         renewer, bufferSize, xattrEncoding, excludeDatanodes, fsAction,
-        tokenKind, tokenService);
+        tokenKind, tokenService, startAfter);
 
     return ugi.doAs(new PrivilegedExceptionAction<Response>() {
       @Override
@@ -836,7 +840,7 @@ public Response run() throws IOException, URISyntaxException {
           return get(ugi, delegation, username, doAsUser,
               path.getAbsolutePath(), op, offset, length, renewer, bufferSize,
               xattrNames, xattrEncoding, excludeDatanodes, fsAction, tokenKind,
-              tokenService, noredirect);
+              tokenService, noredirect, startAfter);
         } finally {
           reset();
         }
@@ -861,7 +865,8 @@ private Response get(
       final FsActionParam fsAction,
       final TokenKindParam tokenKind,
       final TokenServiceParam tokenService,
-      final NoRedirectParam noredirectParam
+      final NoRedirectParam noredirectParam,
+      final StartAfterParam startAfter
       ) throws IOException, URISyntaxException {
     final NameNode namenode = (NameNode)context.getAttribute("name.node");
     final Configuration conf = (Configuration) context
@@ -984,6 +989,16 @@ private Response get(
       np.checkAccess(fullpath, FsAction.getFsAction(fsAction.getValue()));
       return Response.ok().build();
     }
+    case LISTSTATUS_BATCH:
+    {
+      byte[] start = HdfsFileStatus.EMPTY_NAME;
+      if (startAfter != null && startAfter.getValue() != null) {
+        start = startAfter.getValue().getBytes(Charsets.UTF_8);
+      }
+      final DirectoryListing listing = getDirectoryListing(np, fullpath, start);
+      final String js = JsonUtil.toJsonString(listing);
+      return Response.ok(js).type(MediaType.APPLICATION_JSON).build();
+    }
     default:
       throw new UnsupportedOperationException(op + " is not supported");
     }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/web/JsonUtil.java

@@ -96,6 +96,16 @@ public static String toJsonString(final HdfsFileStatus status,
     if (status == null) {
       return null;
     }
+    final Map<String, Object> m = toJsonMap(status);
+    try {
+      return includeType ?
+          toJsonString(FileStatus.class, m) : MAPPER.writeValueAsString(m);
+    } catch (IOException ignored) {
+    }
+    return null;
+  }
+
+  private static Map<String, Object> toJsonMap(HdfsFileStatus status) {
     final Map<String, Object> m = new TreeMap<String, Object>();
     m.put("pathSuffix", status.getLocalName());
     m.put("type", WebHdfsConstants.PathType.valueOf(status));
@@ -121,12 +131,7 @@ public static String toJsonString(final HdfsFileStatus status,
     m.put("fileId", status.getFileId());
     m.put("childrenNum", status.getChildrenNum());
     m.put("storagePolicy", status.getStoragePolicy());
-    try {
+    return m;
-      return includeType ?
-          toJsonString(FileStatus.class, m) : MAPPER.writeValueAsString(m);
-    } catch (IOException ignored) {
-    }
-    return null;
   }
 
   /** Convert an ExtendedBlock to a Json map. */
@@ -227,6 +232,34 @@ private static Map<String, Object> toJsonMap(final LocatedBlock locatedblock
     return m;
   }
 
+  public static String toJsonString(final DirectoryListing listing) throws
+      IOException {
+
+    if (listing == null) {
+      return null;
+    }
+
+    final Map<String, Object> m = new TreeMap<>();
+    m.put("partialListing", toJsonArray(listing.getPartialListing()));
+    m.put("remainingEntries", listing.getRemainingEntries());
+    return MAPPER.writeValueAsString(m);
+  }
+
+  private static Object[] toJsonArray(HdfsFileStatus[] statuses) throws
+      IOException {
+    if (statuses == null) {
+      return null;
+    }
+    if (statuses.length == 0) {
+      return EMPTY_OBJECT_ARRAY;
+    }
+    final Object[] a = new Object[statuses.length];
+    for (int i = 0; i < statuses.length; i++) {
+      a[i] = toJsonMap(statuses[i]);
+    }
+    return a;
+  }
+
   /** Convert a LocatedBlock[] to a Json array. */
   private static Object[] toJsonArray(final List<LocatedBlock> array
       ) throws IOException {

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/WebHDFS.md

@@ -37,6 +37,7 @@ WebHDFS REST API
         * [Truncate a File](#Truncate_a_File)
         * [Status of a File/Directory](#Status_of_a_FileDirectory)
         * [List a Directory](#List_a_Directory)
+        * [Iteratively List a Directory](#Iteratively_List_a_Directory)
     * [Other File System Operations](#Other_File_System_Operations)
         * [Get Content Summary of a Directory](#Get_Content_Summary_of_a_Directory)
         * [Get File Checksum](#Get_File_Checksum)
@@ -143,6 +144,7 @@ The HTTP REST API supports the complete [FileSystem](../../api/org/apache/hadoop
     * [`OPEN`](#Open_and_Read_a_File) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).open)
     * [`GETFILESTATUS`](#Status_of_a_FileDirectory) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getFileStatus)
     * [`LISTSTATUS`](#List_a_Directory) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).listStatus)
+    * [`LISTSTATUS_BATCH`](#Iteratively_List_a_Directory) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).listStatusIterator)
     * [`GETCONTENTSUMMARY`](#Get_Content_Summary_of_a_Directory) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getContentSummary)
     * [`GETFILECHECKSUM`](#Get_File_Checksum) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getFileChecksum)
     * [`GETHOMEDIRECTORY`](#Get_Home_Directory) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getHomeDirectory)
@@ -590,6 +592,109 @@ See also: [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getFileSt
 
 See also: [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).listStatus
 
+### Iteratively List a Directory
+
+* Submit a HTTP GET request.
+
+        curl -i  "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=LISTSTATUS_BATCH&startAfter=<CHILD>"
+
+    The client receives a response with a batch of [`FileStatuses` JSON object](#FileStatuses_JSON_Schema), as well as iteration information:
+
+        HTTP/1.1 200 OK
+        Cache-Control: no-cache
+        Expires: Tue, 30 Aug 2016 16:42:16 GMT
+        Date: Tue, 30 Aug 2016 16:42:16 GMT
+        Pragma: no-cache
+        Expires: Tue, 30 Aug 2016 16:42:16 GMT
+        Date: Tue, 30 Aug 2016 16:42:16 GMT
+        Pragma: no-cache
+        Content-Type: application/json
+        X-FRAME-OPTIONS: SAMEORIGIN
+        Transfer-Encoding: chunked
+        Server: Jetty(6.1.26)
+
+        {
+            "partialListing": [
+                {
+                    "accessTime": 0,
+                    "blockSize": 0,
+                    "childrenNum": 0,
+                    "fileId": 16389,
+                    "group": "supergroup",
+                    "length": 0,
+                    "modificationTime": 1472575493064,
+                    "owner": "andrew",
+                    "pathSuffix": "anotherdir",
+                    "permission": "755",
+                    "replication": 0,
+                    "storagePolicy": 0,
+                    "type": "DIRECTORY"
+                },
+                {
+                    "accessTime": 0,
+                    "blockSize": 0,
+                    "childrenNum": 0,
+                    "fileId": 16386,
+                    "group": "supergroup",
+                    "length": 0,
+                    "modificationTime": 1472575274776,
+                    "owner": "andrew",
+                    "pathSuffix": "somedir",
+                    "permission": "755",
+                    "replication": 0,
+                    "storagePolicy": 0,
+                    "type": "DIRECTORY"
+                }
+            ],
+            "remainingEntries": 1
+        }
+
+
+If `remainingEntries` is non-zero, there are additional entries in the directory.
+To query the next batch, set the `startAfter` parameter to the `pathSuffix` of the last item returned in the current batch. For example:
+
+        curl -i  "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=LISTSTATUS_BATCH&startAfter=somedir"
+
+Which will return the next batch of directory entries:
+
+        HTTP/1.1 200 OK
+        Cache-Control: no-cache
+        Expires: Tue, 30 Aug 2016 16:46:23 GMT
+        Date: Tue, 30 Aug 2016 16:46:23 GMT
+        Pragma: no-cache
+        Expires: Tue, 30 Aug 2016 16:46:23 GMT
+        Date: Tue, 30 Aug 2016 16:46:23 GMT
+        Pragma: no-cache
+        Content-Type: application/json
+        X-FRAME-OPTIONS: SAMEORIGIN
+        Transfer-Encoding: chunked
+        Server: Jetty(6.1.26)
+
+        {
+            "partialListing": [
+                {
+                    "accessTime": 1472575333568,
+                    "blockSize": 1024,
+                    "childrenNum": 0,
+                    "fileId": 16388,
+                    "group": "supergroup",
+                    "length": 224,
+                    "modificationTime": 1472575334222,
+                    "owner": "andrew",
+                    "pathSuffix": "somefile",
+                    "permission": "644",
+                    "replication": 3,
+                    "storagePolicy": 0,
+                    "type": "FILE"
+                }
+            ],
+            "remainingEntries": 0
+        }
+
+Batch size is controlled by the `dfs.ls.limit` option on the NameNode.
+
+See also: [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).listStatusIterator
+
 Other File System Operations
 ----------------------------
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/web/TestWebHDFS.java

@@ -19,6 +19,7 @@
 package org.apache.hadoop.hdfs.web;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
@@ -50,6 +51,7 @@
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.fs.RemoteIterator;
 import org.apache.hadoop.fs.StorageType;
 import org.apache.hadoop.fs.permission.FsAction;
 import org.apache.hadoop.fs.permission.FsPermission;
@@ -299,11 +301,50 @@ public Void run() throws IOException, URISyntaxException {
                   WebHdfsConstants.WEBHDFS_SCHEME);
               Path d = new Path("/my-dir");
             Assert.assertTrue(fs.mkdirs(d));
-            for (int i=0; i < listLimit*3; i++) {
+            // Iterator should have no items when dir is empty
-              Path p = new Path(d, "file-"+i);
+            RemoteIterator<FileStatus> it = fs.listStatusIterator(d);
+            assertFalse(it.hasNext());
+            Path p = new Path(d, "file-"+0);
+            Assert.assertTrue(fs.createNewFile(p));
+            // Iterator should have an item when dir is not empty
+            it = fs.listStatusIterator(d);
+            assertTrue(it.hasNext());
+            it.next();
+            assertFalse(it.hasNext());
+            for (int i=1; i < listLimit*3; i++) {
+              p = new Path(d, "file-"+i);
               Assert.assertTrue(fs.createNewFile(p));
             }
-            Assert.assertEquals(listLimit*3, fs.listStatus(d).length);
+            // Check the FileStatus[] listing
+            FileStatus[] statuses = fs.listStatus(d);
+            Assert.assertEquals(listLimit*3, statuses.length);
+            // Check the iterator-based listing
+            GenericTestUtils.setLogLevel(WebHdfsFileSystem.LOG, Level.TRACE);
+            GenericTestUtils.setLogLevel(NamenodeWebHdfsMethods.LOG, Level
+                .TRACE);
+            it = fs.listStatusIterator(d);
+            int count = 0;
+            while (it.hasNext()) {
+              FileStatus stat = it.next();
+              assertEquals("FileStatuses not equal", statuses[count], stat);
+              count++;
+            }
+            assertEquals("Different # of statuses!", statuses.length, count);
+            // Do some more basic iterator tests
+            it = fs.listStatusIterator(d);
+            // Try advancing the iterator without calling hasNext()
+            for (int i = 0; i < statuses.length; i++) {
+              FileStatus stat = it.next();
+              assertEquals("FileStatuses not equal", statuses[i], stat);
+            }
+            assertFalse("No more items expected", it.hasNext());
+            // Try doing next when out of items
+            try {
+              it.next();
+              fail("Iterator should error if out of elements.");
+            } catch (IllegalStateException e) {
+              // pass
+            }
             return null;
           }
         });
@@ -446,9 +487,9 @@ public void testWebHdfsDeleteSnapshot() throws Exception {
 
       // delete the two snapshots
       webHdfs.deleteSnapshot(foo, "s1");
-      Assert.assertFalse(webHdfs.exists(s1path));
+      assertFalse(webHdfs.exists(s1path));
       webHdfs.deleteSnapshot(foo, spath.getName());
-      Assert.assertFalse(webHdfs.exists(spath));
+      assertFalse(webHdfs.exists(spath));
     } finally {
       if (cluster != null) {
         cluster.shutdown();
@@ -504,12 +545,12 @@ public void testWebHdfsRenameSnapshot() throws Exception {
 
       // rename s1 to s2
       webHdfs.renameSnapshot(foo, "s1", "s2");
-      Assert.assertFalse(webHdfs.exists(s1path));
+      assertFalse(webHdfs.exists(s1path));
       final Path s2path = SnapshotTestHelper.getSnapshotRoot(foo, "s2");
       Assert.assertTrue(webHdfs.exists(s2path));
 
       webHdfs.deleteSnapshot(foo, "s2");
-      Assert.assertFalse(webHdfs.exists(s2path));
+      assertFalse(webHdfs.exists(s2path));
     } finally {
       if (cluster != null) {
         cluster.shutdown();

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/web/TestWebHdfsUrl.java

@@ -39,6 +39,7 @@
 import org.apache.hadoop.hdfs.web.resources.DoAsParam;
 import org.apache.hadoop.hdfs.web.resources.GetOpParam;
 import org.apache.hadoop.hdfs.web.resources.PutOpParam;
+import org.apache.hadoop.hdfs.web.resources.StartAfterParam;
 import org.apache.hadoop.hdfs.web.resources.TokenArgumentParam;
 import org.apache.hadoop.hdfs.web.resources.UserParam;
 import org.apache.hadoop.hdfs.web.resources.FsActionParam;
@@ -306,6 +307,30 @@ public void testCheckAccessUrl() throws IOException {
         },
         checkAccessUrl);
   }
+
+  @Test(timeout=60000)
+  public void testBatchedListingUrl() throws Exception {
+    Configuration conf = new Configuration();
+
+    UserGroupInformation ugi =
+        UserGroupInformation.createRemoteUser("test-user");
+    UserGroupInformation.setLoginUser(ugi);
+
+    WebHdfsFileSystem webhdfs = getWebHdfsFileSystem(ugi, conf);
+    Path fsPath = new Path("/p1");
+
+    final StartAfterParam startAfter =
+        new StartAfterParam("last");
+    URL url = webhdfs.toUrl(GetOpParam.Op.LISTSTATUS_BATCH,
+        fsPath, startAfter);
+    checkQueryParams(
+        new String[]{
+            GetOpParam.Op.LISTSTATUS_BATCH.toQueryString(),
+            new UserParam(ugi.getShortUserName()).toString(),
+            StartAfterParam.NAME + "=" + "last"
+        },
+        url);
+  }
   
   private void checkQueryParams(String[] expected, URL url) {
     Arrays.sort(expected);

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/web/resources/TestParam.java

@@ -453,4 +453,11 @@ public void testFsActionParam() {
       LOG.info("EXPECTED: " + e);
     }
   }
+
+  @Test
+  public void testStartAfterParam() throws Exception {
+    String s = "/helloWorld";
+    StartAfterParam param = new StartAfterParam(s);
+    Assert.assertEquals(s, param.getValue());
+  }
 }