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}