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
019package org.apache.hadoop.mapred.lib;
020
021import java.io.*;
022import java.lang.reflect.*;
023
024import org.apache.hadoop.fs.FileSystem;
025
026import org.apache.hadoop.mapred.*;
027import org.apache.hadoop.classification.InterfaceAudience;
028import org.apache.hadoop.classification.InterfaceStability;
029import org.apache.hadoop.conf.Configuration;
030
031/**
032 * A generic RecordReader that can hand out different recordReaders
033 * for each chunk in a {@link CombineFileSplit}.
034 * A CombineFileSplit can combine data chunks from multiple files. 
035 * This class allows using different RecordReaders for processing
036 * these data chunks from different files.
037 * @see CombineFileSplit
038 */
039@InterfaceAudience.Public
040@InterfaceStability.Stable
041public class CombineFileRecordReader<K, V> implements RecordReader<K, V> {
042
043  static final Class [] constructorSignature = new Class [] 
044                                         {CombineFileSplit.class, 
045                                          Configuration.class, 
046                                          Reporter.class,
047                                          Integer.class};
048
049  protected CombineFileSplit split;
050  protected JobConf jc;
051  protected Reporter reporter;
052  protected Class<RecordReader<K, V>> rrClass;
053  protected Constructor<RecordReader<K, V>> rrConstructor;
054  protected FileSystem fs;
055  
056  protected int idx;
057  protected long progress;
058  protected RecordReader<K, V> curReader;
059  
060  public boolean next(K key, V value) throws IOException {
061
062    while ((curReader == null) || !curReader.next(key, value)) {
063      if (!initNextRecordReader()) {
064        return false;
065      }
066    }
067    return true;
068  }
069
070  public K createKey() {
071    return curReader.createKey();
072  }
073  
074  public V createValue() {
075    return curReader.createValue();
076  }
077  
078  /**
079   * return the amount of data processed
080   */
081  public long getPos() throws IOException {
082    return progress;
083  }
084  
085  public void close() throws IOException {
086    if (curReader != null) {
087      curReader.close();
088      curReader = null;
089    }
090  }
091  
092  /**
093   * return progress based on the amount of data processed so far.
094   */
095  public float getProgress() throws IOException {
096    return Math.min(1.0f,  progress/(float)(split.getLength()));
097  }
098  
099  /**
100   * A generic RecordReader that can hand out different recordReaders
101   * for each chunk in the CombineFileSplit.
102   */
103  public CombineFileRecordReader(JobConf job, CombineFileSplit split, 
104                                 Reporter reporter,
105                                 Class<RecordReader<K, V>> rrClass)
106    throws IOException {
107    this.split = split;
108    this.jc = job;
109    this.rrClass = rrClass;
110    this.reporter = reporter;
111    this.idx = 0;
112    this.curReader = null;
113    this.progress = 0;
114
115    try {
116      rrConstructor = rrClass.getDeclaredConstructor(constructorSignature);
117      rrConstructor.setAccessible(true);
118    } catch (Exception e) {
119      throw new RuntimeException(rrClass.getName() + 
120                                 " does not have valid constructor", e);
121    }
122    initNextRecordReader();
123  }
124  
125  /**
126   * Get the record reader for the next chunk in this CombineFileSplit.
127   */
128  protected boolean initNextRecordReader() throws IOException {
129
130    if (curReader != null) {
131      curReader.close();
132      curReader = null;
133      if (idx > 0) {
134        progress += split.getLength(idx-1);    // done processing so far
135      }
136    }
137
138    // if all chunks have been processed, nothing more to do.
139    if (idx == split.getNumPaths()) {
140      return false;
141    }
142
143    // get a record reader for the idx-th chunk
144    try {
145      curReader =  rrConstructor.newInstance(new Object [] 
146                            {split, jc, reporter, Integer.valueOf(idx)});
147
148      // setup some helper config variables.
149      jc.set(JobContext.MAP_INPUT_FILE, split.getPath(idx).toString());
150      jc.setLong(JobContext.MAP_INPUT_START, split.getOffset(idx));
151      jc.setLong(JobContext.MAP_INPUT_PATH, split.getLength(idx));
152    } catch (Exception e) {
153      throw new RuntimeException (e);
154    }
155    idx++;
156    return true;
157  }
158}