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 */
018package org.apache.hadoop.mapreduce.lib.join;
019
020import java.io.ByteArrayInputStream;
021import java.io.ByteArrayOutputStream;
022import java.io.DataInputStream;
023import java.io.DataOutputStream;
024import java.io.IOException;
025
026import org.apache.hadoop.classification.InterfaceAudience;
027import org.apache.hadoop.classification.InterfaceStability;
028import org.apache.hadoop.io.Writable;
029
030/**
031 * This class provides an implementation of ResetableIterator. This
032 * implementation uses a byte array to store elements added to it.
033 */
034@InterfaceAudience.Public
035@InterfaceStability.Stable
036public class StreamBackedIterator<X extends Writable>
037    implements ResetableIterator<X> {
038
039  private static class ReplayableByteInputStream extends ByteArrayInputStream {
040    public ReplayableByteInputStream(byte[] arr) {
041      super(arr);
042    }
043    public void resetStream() {
044      mark = 0;
045      reset();
046    }
047  }
048
049  private ByteArrayOutputStream outbuf = new ByteArrayOutputStream();
050  private DataOutputStream outfbuf = new DataOutputStream(outbuf);
051  private ReplayableByteInputStream inbuf;
052  private DataInputStream infbuf;
053
054  public StreamBackedIterator() { }
055
056  public boolean hasNext() {
057    return infbuf != null && inbuf.available() > 0;
058  }
059
060  public boolean next(X val) throws IOException {
061    if (hasNext()) {
062      inbuf.mark(0);
063      val.readFields(infbuf);
064      return true;
065    }
066    return false;
067  }
068
069  public boolean replay(X val) throws IOException {
070    inbuf.reset();
071    if (0 == inbuf.available())
072      return false;
073    val.readFields(infbuf);
074    return true;
075  }
076
077  public void reset() {
078    if (null != outfbuf) {
079      inbuf = new ReplayableByteInputStream(outbuf.toByteArray());
080      infbuf =  new DataInputStream(inbuf);
081      outfbuf = null;
082    }
083    inbuf.resetStream();
084  }
085
086  public void add(X item) throws IOException {
087    item.write(outfbuf);
088  }
089
090  public void close() throws IOException {
091    if (null != infbuf)
092      infbuf.close();
093    if (null != outfbuf)
094      outfbuf.close();
095  }
096
097  public void clear() {
098    if (null != inbuf)
099      inbuf.resetStream();
100    outbuf.reset();
101    outfbuf = new DataOutputStream(outbuf);
102  }
103}