Java tutorial
/** * 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 com.geneix.bottle; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FSDataInputStream; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.fs.Seekable; import org.apache.hadoop.io.LongWritable; import org.apache.hadoop.io.Text; import org.apache.hadoop.io.compress.CodecPool; import org.apache.hadoop.io.compress.CompressionCodec; import org.apache.hadoop.io.compress.CompressionCodecFactory; import org.apache.hadoop.io.compress.Decompressor; import org.apache.hadoop.mapreduce.InputSplit; import org.apache.hadoop.mapreduce.RecordReader; import org.apache.hadoop.mapreduce.TaskAttemptContext; import org.apache.hadoop.mapreduce.lib.input.FileSplit; import org.apache.hadoop.mapreduce.lib.input.LineRecordReader; import java.io.IOException; /** * Treats keys as offset in file and value as line. */ @InterfaceAudience.LimitedPrivate({ "MapReduce", "Pig" }) @InterfaceStability.Evolving public class WordRecordReader extends RecordReader<LongWritable, Word> { public static final String MAX_WORD_LENGTH = "mapreduce.input.wordrecordreader.word.maxlength"; private static final Log LOG = LogFactory.getLog(WordRecordReader.class); private final WordParser wordParser = new FakeWordParser(); private long start; private long pos; private long end; private WordReader in; private FSDataInputStream fileIn; private Seekable filePosition; private int maxWordLength; private LongWritable key; private Text value; private Decompressor decompressor; private boolean isCompressedInput = false; public WordRecordReader() { } public void initialize(InputSplit genericSplit, TaskAttemptContext context) throws IOException { if (LOG.isInfoEnabled()) { LOG.info("Initializing WordRecordReader"); } FileSplit split = (FileSplit) genericSplit; Configuration job = context.getConfiguration(); this.maxWordLength = job.getInt(MAX_WORD_LENGTH, Integer.MAX_VALUE); start = split.getStart(); end = start + split.getLength(); final Path file = split.getPath(); // open the file and seek to the start of the split final FileSystem fs = file.getFileSystem(job); fileIn = fs.open(file); CompressionCodec codec = new CompressionCodecFactory(job).getCodec(file); if (null != codec) { throw new IOException("Cannot handle compressed files right now"); } else { fileIn.seek(start); in = new WordReader(fileIn, job); filePosition = fileIn; } // If this is not the first split, we always throw away first record // because we always (except the last split) read one extra line in // next() method. if (start != 0) { start += in.readWord(new Text(), 0, maxBytesToConsume(start)); } this.pos = start; } private int maxBytesToConsume(long pos) { return isCompressedInput ? Integer.MAX_VALUE : (int) Math.max(Math.min(Integer.MAX_VALUE, end - pos), maxWordLength); } private long getFilePosition() throws IOException { long retVal; if (isCompressedInput && null != filePosition) { retVal = filePosition.getPos(); } else { retVal = pos; } return retVal; } //TODO: I'm not sure this works exactly correctly with the code point reader private int skipUtfByteOrderMark() throws IOException { // Strip BOM(Byte Order Mark) // Text only support UTF-8, we only need to check UTF-8 BOM // (0xEF,0xBB,0xBF) at the start of the text stream. int newMaxLineLength = (int) Math.min(3L + (long) maxWordLength, Integer.MAX_VALUE); int newSize = in.readWord(value, newMaxLineLength, maxBytesToConsume(pos)); // Even we read 3 extra bytes for the first line, // we won't alter existing behavior (no backwards incompat issue). // Because the newSize is less than maxLineLength and // the number of bytes copied to Text is always no more than newSize. // If the return size from readLine is not less than maxLineLength, // we will discard the current line and read the next line. pos += newSize; int textLength = value.getLength(); byte[] textBytes = value.getBytes(); if ((textLength >= 3) && (textBytes[0] == (byte) 0xEF) && (textBytes[1] == (byte) 0xBB) && (textBytes[2] == (byte) 0xBF)) { // find UTF-8 BOM, strip it. LOG.info("Found UTF-8 BOM and skipped it"); textLength -= 3; newSize -= 3; if (textLength > 0) { // It may work to use the same buffer and not do the copyBytes textBytes = value.copyBytes(); value.set(textBytes, 3, textLength); } else { value.clear(); } } return newSize; } public boolean nextKeyValue() throws IOException { if (LOG.isInfoEnabled()) { LOG.info("Getting next kvp"); LOG.info(String.format("POS:%s; END:%s; MAX_LENGTH:%s;", pos, end, maxWordLength)); } if (key == null) { key = new LongWritable(); } key.set(pos); if (value == null) { value = new Text(); } int newSize = 0; // We always read one extra line, which lies outside the upper // split limit i.e. (end - 1) while (getFilePosition() <= end) { //|| in.needAdditionalRecordAfterSplit()) { if (pos == 0) { newSize = skipUtfByteOrderMark(); } else { newSize = in.readWord(value, maxWordLength, maxBytesToConsume(pos)); pos += newSize; } if ((newSize == 0) || (newSize < maxWordLength)) { break; } // line too long. try again if (LOG.isInfoEnabled()) { LOG.info("Skipped word of size " + newSize + " at pos " + (pos - newSize)); } } if (newSize == 0) { if (LOG.isInfoEnabled()) { LOG.info("Empty word?"); } key = null; value = null; return false; } else { return true; } } @Override public LongWritable getCurrentKey() { return key; } @Override public Word getCurrentValue() { return Word.fromText(value, wordParser); } /** * Get the progress within the split */ public float getProgress() throws IOException { if (start == end) { return 0.0f; } else { return Math.min(1.0f, (getFilePosition() - start) / (float) (end - start)); } } public synchronized void close() throws IOException { try { if (in != null) { in.close(); } } finally { if (decompressor != null) { CodecPool.returnDecompressor(decompressor); } } } }