hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocol/CacheDirectiveIterator.java

/**
 * 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.protocol;

import java.io.IOException;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.BatchedRemoteIterator;

/**
 * CacheDirectiveIterator is a remote iterator that iterates cache directives.
 * It supports retrying in case of namenode failover.
 */
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class CacheDirectiveIterator
    extends BatchedRemoteIterator<Long, CacheDirectiveEntry> {

  private final CacheDirectiveInfo filter;
  private final ClientProtocol namenode;

  public CacheDirectiveIterator(ClientProtocol namenode,
      CacheDirectiveInfo filter) {
    super(Long.valueOf(0));
    this.namenode = namenode;
    this.filter = filter;
  }

  @Override
  public BatchedEntries<CacheDirectiveEntry> makeRequest(Long prevKey)
      throws IOException {
    return namenode.listCacheDirectives(prevKey, filter);
  }

  @Override
  public Long elementToPrevKey(CacheDirectiveEntry entry) {
    return entry.getInfo().getId();
  }
}