001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.hadoop.mapreduce.lib.join;
019    
020    import java.io.IOException;
021    import java.util.ArrayList;
022    import java.util.Iterator;
023    
024    import org.apache.hadoop.classification.InterfaceAudience;
025    import org.apache.hadoop.classification.InterfaceStability;
026    import org.apache.hadoop.conf.Configuration;
027    import org.apache.hadoop.io.Writable;
028    import org.apache.hadoop.io.WritableUtils;
029    import org.apache.hadoop.util.ReflectionUtils;
030    
031    /**
032     * This class provides an implementation of ResetableIterator. The
033     * implementation uses an {@link java.util.ArrayList} to store elements
034     * added to it, replaying them as requested.
035     * Prefer {@link StreamBackedIterator}.
036     */
037    @InterfaceAudience.Public
038    @InterfaceStability.Stable
039    public class ArrayListBackedIterator<X extends Writable>
040        implements ResetableIterator<X> {
041    
042      private Iterator<X> iter;
043      private ArrayList<X> data;
044      private X hold = null;
045      private Configuration conf = new Configuration();
046    
047      public ArrayListBackedIterator() {
048        this(new ArrayList<X>());
049      }
050    
051      public ArrayListBackedIterator(ArrayList<X> data) {
052        this.data = data;
053        this.iter = this.data.iterator();
054      }
055    
056      public boolean hasNext() {
057        return iter.hasNext();
058      }
059    
060      public boolean next(X val) throws IOException {
061        if (iter.hasNext()) {
062          ReflectionUtils.copy(conf, iter.next(), val);
063          if (null == hold) {
064            hold = WritableUtils.clone(val, null);
065          } else {
066            ReflectionUtils.copy(conf, val, hold);
067          }
068          return true;
069        }
070        return false;
071      }
072    
073      public boolean replay(X val) throws IOException {
074        ReflectionUtils.copy(conf, hold, val);
075        return true;
076      }
077    
078      public void reset() {
079        iter = data.iterator();
080      }
081    
082      public void add(X item) throws IOException {
083        data.add(WritableUtils.clone(item, null));
084      }
085    
086      public void close() throws IOException {
087        iter = null;
088        data = null;
089      }
090    
091      public void clear() {
092        data.clear();
093        reset();
094      }
095    }