| /** |
| * 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.fs; |
| |
| import java.io.IOException; |
| import java.util.List; |
| import java.util.NoSuchElementException; |
| |
| /** |
| * A RemoteIterator that fetches elements in batches. |
| */ |
| public abstract class BatchedRemoteIterator<K, E> implements RemoteIterator<E> { |
| public interface BatchedEntries<E> { |
| public E get(int i); |
| public int size(); |
| public boolean hasMore(); |
| } |
| |
| public static class BatchedListEntries<E> implements BatchedEntries<E> { |
| private final List<E> entries; |
| private final boolean hasMore; |
| |
| public BatchedListEntries(List<E> entries, boolean hasMore) { |
| this.entries = entries; |
| this.hasMore = hasMore; |
| } |
| |
| public E get(int i) { |
| return entries.get(i); |
| } |
| |
| public int size() { |
| return entries.size(); |
| } |
| |
| public boolean hasMore() { |
| return hasMore; |
| } |
| } |
| |
| private K prevKey; |
| private BatchedEntries<E> entries; |
| private int idx; |
| |
| public BatchedRemoteIterator(K prevKey) { |
| this.prevKey = prevKey; |
| this.entries = null; |
| this.idx = -1; |
| } |
| |
| /** |
| * Perform the actual remote request. |
| * |
| * @param prevKey The key to send. |
| * @return A list of replies. |
| */ |
| public abstract BatchedEntries<E> makeRequest(K prevKey) throws IOException; |
| |
| private void makeRequest() throws IOException { |
| idx = 0; |
| entries = null; |
| entries = makeRequest(prevKey); |
| if (entries.size() == 0) { |
| entries = null; |
| } |
| } |
| |
| private void makeRequestIfNeeded() throws IOException { |
| if (idx == -1) { |
| makeRequest(); |
| } else if ((entries != null) && (idx >= entries.size())) { |
| if (!entries.hasMore()) { |
| // Last time, we got fewer entries than requested. |
| // So we should be at the end. |
| entries = null; |
| } else { |
| makeRequest(); |
| } |
| } |
| } |
| |
| @Override |
| public boolean hasNext() throws IOException { |
| makeRequestIfNeeded(); |
| return (entries != null); |
| } |
| |
| /** |
| * Return the next list key associated with an element. |
| */ |
| public abstract K elementToPrevKey(E element); |
| |
| @Override |
| public E next() throws IOException { |
| makeRequestIfNeeded(); |
| if (entries == null) { |
| throw new NoSuchElementException(); |
| } |
| E entry = entries.get(idx++); |
| prevKey = elementToPrevKey(entry); |
| return entry; |
| } |
| } |