研究MapReduce原始碼之實現自定義LineRecordReader完成多行讀取檔案內容
阿新 • • 發佈：2019-02-07
TextInputFormat是Hadoop預設的資料輸入格式,但是它只能一行一行的讀記錄，如果要讀取多行怎麼辦？
很簡單 自己寫一個輸入格式，然後寫一個對應的Recordreader就可以了，但是要實現確不是這麼簡單的
首先看看TextInputFormat是怎麼實現一行一行讀取的
大家看一看原始碼
public class TextInputFormat extends FileInputFormat<LongWritable, Text> {
@Override
public RecordReader<LongWritable, Text>
createRecordReader(InputSplit split,
TaskAttemptContext context) {
String delimiter = context.getConfiguration().get(
"textinputformat.record.delimiter" 我們只要看第一個createRecordReader方法即可，從原始碼分析可知，它new了一個LineRecordReader，那麼我們再來看看LineRecordReader的原始碼，看看這小子的內部世界
public class （裡面96-97行
in = new CompressedSplitLineReader(cIn, job, this.recordDelimiterBytes);
108-109行
in = new CompressedSplitLineReader(cIn, job,this.recordDelimiterBytes);
這是用來壓縮的，大家不用管，知道有這回事就行了
其實這兩個類都繼承自SplitLineReader，是與壓縮有關的，後面我們自定義的時候不用改，貼上複製過來就行。
）
從上面發現了一個問題，看原始碼的第57行
private SplitLineReader in;它引入了一個SplitLineReader 類,用這個小子來讀取每一行，不信？你看原始碼的182-197行，如下（我的基於2.6.4版本的原始碼，不同的版本程式碼應該差別不大）
while (getFilePosition() <= end || in.needAdditionalRecordAfterSplit()) {
if (pos == 0) {
newSize = skipUtfByteOrderMark();
} else {
newSize = in.readLine(value, maxLineLength, maxBytesToConsume(pos));
pos += newSize;
}
if ((newSize == 0) || (newSize < maxLineLength)) {
break;
}
// line too long. try again
LOG.info("Skipped line of size " + newSize + " at pos " +
(pos - newSize));
}發現沒有 ===》 newSize = in.readLine(value, maxLineLength, maxBytesToConsume(pos));
它用了SplitLineReader 裡面的一個方法readLine來讀取，所以我們就得繼續跟蹤去看看SplitLineReader 這個小子的廬山真面目，下面看SplitLineReader 的原始碼
public class SplitLineReader extends org.apache.hadoop.util.LineReader {
public SplitLineReader(InputStream in, byte[] recordDelimiterBytes) {
super(in, recordDelimiterBytes);
}
public SplitLineReader(InputStream in, Configuration conf,
byte[] recordDelimiterBytes) throws IOException {
super(in, conf, recordDelimiterBytes);
}
public boolean needAdditionalRecordAfterSplit() {
return false;
}
}發現這傢伙繼承自LineReader（快接近我們的目標了，堅持看下去），發現這小子裡面根本就沒有readLine方法，大家是不是覺得我在忽悠大家，哈哈，我沒有忽悠大家，它原始碼裡面確實沒有，但是但是，它可是繼承了LineReader這個類，說不定他的父類LineReader有了，好，不信我們去看看LineReader
繼續跟蹤到LineReader的原始碼
public class LineReader implements Closeable {
private static final int DEFAULT_BUFFER_SIZE = 64 * 1024;
private int bufferSize = DEFAULT_BUFFER_SIZE;
private InputStream in;
private byte[] buffer;
// the number of bytes of real data in the buffer
private int bufferLength = 0;
// the current position in the buffer
private int bufferPosn = 0;
private static final byte CR = '\r';
private static final byte LF = '\n';
// The line delimiter
private final byte[] recordDelimiterBytes;
/**
* Create a line reader that reads from the given stream using the
* default buffer-size (64k).
* @param in The input stream
* @throws IOException
*/
public LineReader(InputStream in) {
this(in, DEFAULT_BUFFER_SIZE);
}
/**
* Create a line reader that reads from the given stream using the
* given buffer-size.
* @param in The input stream
* @param bufferSize Size of the read buffer
* @throws IOException
*/
public LineReader(InputStream in, int bufferSize) {
this.in = in;
this.bufferSize = bufferSize;
this.buffer = new byte[this.bufferSize];
this.recordDelimiterBytes = null;
}
/**
* Create a line reader that reads from the given stream using the
* <code>io.file.buffer.size</code> specified in the given
* <code>Configuration</code>.
* @param in input stream
* @param conf configuration
* @throws IOException
*/
public LineReader(InputStream in, Configuration conf) throws IOException {
this(in, conf.getInt("io.file.buffer.size", DEFAULT_BUFFER_SIZE));
}
/**
* Create a line reader that reads from the given stream using the
* default buffer-size, and using a custom delimiter of array of
* bytes.
* @param in The input stream
* @param recordDelimiterBytes The delimiter
*/
public LineReader(InputStream in, byte[] recordDelimiterBytes) {
this.in = in;
this.bufferSize = DEFAULT_BUFFER_SIZE;
this.buffer = new byte[this.bufferSize];
this.recordDelimiterBytes = recordDelimiterBytes;
}
/**
* Create a line reader that reads from the given stream using the
* given buffer-size, and using a custom delimiter of array of
* bytes.
* @param in The input stream
* @param bufferSize Size of the read buffer
* @param recordDelimiterBytes The delimiter
* @throws IOException
*/
public LineReader(InputStream in, int bufferSize,
byte[] recordDelimiterBytes) {
this.in = in;
this.bufferSize = bufferSize;
this.buffer = new byte[this.bufferSize];
this.recordDelimiterBytes = recordDelimiterBytes;
}
/**
* Create a line reader that reads from the given stream using the
* <code>io.file.buffer.size</code> specified in the given
* <code>Configuration</code>, and using a custom delimiter of array of
* bytes.
* @param in input stream
* @param conf configuration
* @param recordDelimiterBytes The delimiter
* @throws IOException
*/
public LineReader(InputStream in, Configuration conf,
byte[] recordDelimiterBytes) throws IOException {
this.in = in;
this.bufferSize = conf.getInt("io.file.buffer.size", DEFAULT_BUFFER_SIZE);
this.buffer = new byte[this.bufferSize];
this.recordDelimiterBytes = recordDelimiterBytes;
}
/**
* Close the underlying stream.
* @throws IOException
*/
public void close() throws IOException {
in.close();
}
/**
* Read one line from the InputStream into the given Text.
*
* @param str the object to store the given line (without newline)
* @param maxLineLength the maximum number of bytes to store into str;
* the rest of the line is silently discarded.
* @param maxBytesToConsume the maximum number of bytes to consume
* in this call. This is only a hint, because if the line cross
* this threshold, we allow it to happen. It can overshoot
* potentially by as much as one buffer length.
*
* @return the number of bytes read including the (longest) newline
* found.
*
* @throws IOException if the underlying stream throws
*/
public int readLine(Text str, int maxLineLength,
int maxBytesToConsume) throws IOException {
if (this.recordDelimiterBytes != null) {
return readCustomLine(str, maxLineLength, maxBytesToConsume);
} else {
return readDefaultLine(str, maxLineLength, maxBytesToConsume);
}
}
protected int fillBuffer(InputStream in, byte[] buffer, boolean inDelimiter)
throws IOException {
return in.read(buffer);
}
/**
* Read a line terminated by one of CR, LF, or CRLF.
*/
private int readDefaultLine(Text str, int maxLineLength, int maxBytesToConsume)
throws IOException {
/* We're reading data from in, but the head of the stream may be
* already buffered in buffer, so we have several cases:
* 1. No newline characters are in the buffer, so we need to copy
* everything and read another buffer from the stream.
* 2. An unambiguously terminated line is in buffer, so we just
* copy to str.
* 3. Ambiguously terminated line is in buffer, i.e. buffer ends
* in CR. In this case we copy everything up to CR to str, but
* we also need to see what follows CR: if it's LF, then we
* need consume LF as well, so next call to readLine will read
* from after that.
* We use a flag prevCharCR to signal if previous character was CR
* and, if it happens to be at the end of the buffer, delay
* consuming it until we have a chance to look at the char that
* follows.
*/
str.clear();
int txtLength = 0; //tracks str.getLength(), as an optimization
int newlineLength = 0; //length of terminating newline
boolean prevCharCR = false; //true of prev char was CR
long bytesConsumed = 0;
do {
int startPosn = bufferPosn; //starting from where we left off the last time
if (bufferPosn >= bufferLength) {
startPosn = bufferPosn = 0;
if (prevCharCR) {
++bytesConsumed; //account for CR from previous read
}
bufferLength = fillBuffer(in, buffer, prevCharCR);
if (bufferLength <= 0) {
break; // EOF
}
}
for (; bufferPosn < bufferLength; ++bufferPosn) { //search for newline
if (buffer[bufferPosn] == LF) {
newlineLength = (prevCharCR) ? 2 : 1;
++bufferPosn; // at next invocation proceed from following byte
break;
}
if (prevCharCR) { //CR + notLF, we are at notLF
newlineLength = 1;
break;
}
prevCharCR = (buffer[bufferPosn] == CR);
}
int readLength = bufferPosn - startPosn;
if (prevCharCR && newlineLength == 0) {
--readLength; //CR at the end of the buffer
}
bytesConsumed += readLength;
int appendLength = readLength - newlineLength;
if (appendLength > maxLineLength - txtLength) {
appendLength = maxLineLength - txtLength;
}
if (appendLength > 0) {
str.append(buffer, startPosn, appendLength);
txtLength += appendLength;
}
} while (newlineLength == 0 && bytesConsumed < maxBytesToConsume);
if (bytesConsumed > Integer.MAX_VALUE) {
throw new IOException("Too many bytes before newline: " + bytesConsumed);
}
return (int)bytesConsumed;
}
/**
* Read a line terminated by a custom delimiter.
*/
private int readCustomLine(Text str, int maxLineLength, int maxBytesToConsume)
throws IOException {
/* We're reading data from inputStream, but the head of the stream may be
* already captured in the previous buffer, so we have several cases:
*
* 1. The buffer tail does not contain any character sequence which
* matches with the head of delimiter. We count it as a
* ambiguous byte count = 0
*
* 2. The buffer tail contains a X number of characters,
* that forms a sequence, which matches with the
* head of delimiter. We count ambiguous byte count = X
*
* // *** eg: A segment of input file is as follows
*
* " record 1792: I found this bug very interesting and
* I have completely read about it. record 1793: This bug
* can be solved easily record 1794: This ."
*
* delimiter = "record";
*
* supposing:- String at the end of buffer =
* "I found this bug very interesting and I have completely re"
* There for next buffer = "ad about it. record 179 ...."
*
* The matching characters in the input
* buffer tail and delimiter head = "re"
* Therefore, ambiguous byte count = 2 **** //
*
* 2.1 If the following bytes are the remaining characters of
* the delimiter, then we have to capture only up to the starting
* position of delimiter. That means, we need not include the
* ambiguous characters in str.
*
* 2.2 If the following bytes are not the remaining characters of
* the delimiter ( as mentioned in the example ),
* then we have to include the ambiguous characters in str.
*/
str.clear();
int txtLength = 0; // tracks str.getLength(), as an optimization
long bytesConsumed = 0;
int delPosn = 0;
int ambiguousByteCount=0; // To capture the ambiguous characters count
do {
int startPosn = bufferPosn; // Start from previous end position
if (bufferPosn >= bufferLength) {
startPosn = bufferPosn = 0;
bufferLength = fillBuffer(in, buffer, ambiguousByteCount > 0);
if (bufferLength <= 0) {
if (ambiguousByteCount > 0) {
str.append(recordDelimiterBytes, 0, ambiguousByteCount);
bytesConsumed += ambiguousByteCount;
}
break; // EOF
}
}
for (; bufferPosn < bufferLength; ++bufferPosn) {
if (buffer[bufferPosn] == recordDelimiterBytes[delPosn]) {
delPosn++;
if (delPosn >= recordDelimiterBytes.length) {
bufferPosn++;
break;
}
} else if (delPosn != 0) {
bufferPosn--;
delPosn = 0;
}
}
int readLength = bufferPosn - startPosn;
bytesConsumed += readLength;
int appendLength = readLength - delPosn;
if (appendLength > maxLineLength - txtLength) {
appendLength = maxLineLength - txtLength;
}
bytesConsumed += ambiguousByteCount;
if (appendLength >= 0 && ambiguousByteCount > 0) {
//appending the ambiguous characters (refer case 2.2)
str.append(recordDelimiterBytes, 0, ambiguousByteCount);
ambiguousByteCount = 0;
// since it is now certain that the split did not split a delimiter we
// should not read the next record: clear the flag otherwise duplicate
// records could be generated
unsetNeedAdditionalRecordAfterSplit();
}
if (appendLength > 0) {
str.append(buffer, startPosn, appendLength);
txtLength += appendLength;
}
if (bufferPosn >= bufferLength) {
if (delPosn > 0 && delPosn < recordDelimiterBytes.length) {
ambiguousByteCount = delPosn;
bytesConsumed -= ambiguousByteCount; //to be consumed in next
}
}
} while (delPosn < recordDelimiterBytes.length
&& bytesConsumed < maxBytesToConsume);
if (bytesConsumed > Integer.MAX_VALUE) {
throw new IOException("Too many bytes before delimiter: " + bytesConsumed);
}
return (int) bytesConsumed;
}
/**
* Read from the InputStream into the given Text.
* @param str the object to store the given line
* @param maxLineLength the maximum number of bytes to store into str.
* @return the number of bytes read including the newline
* @throws IOException if the underlying stream throws
*/
public int readLine(Text str, int maxLineLength) throws IOException {
return readLine(str, maxLineLength, Integer.MAX_VALUE);
}
/**
* Read from the InputStream into the given Text.
* @param str the object to store the given line
* @return the number of bytes read including the newline
* @throws IOException if the underlying stream throws
*/
public int readLine(Text str) throws IOException {
return readLine(str, Integer.MAX_VALUE, Integer.MAX_VALUE);
}
protected int getBufferPosn() {
return bufferPosn;
}
protected int getBufferSize() {
return bufferSize;
}
protected void unsetNeedAdditionalRecordAfterSplit() {
// needed for custom multi byte line delimiters only
// see MAPREDUCE-6549 for details
}
}它裡面有很多方法，真的有我們要的readLine方法，說明我的推斷沒有錯，沒有忽悠大家，它過載了好幾個readLine方法
其他我們不去管，我們只管對我們有用的，如下
public int readLine(Text str, int maxLineLength,
int maxBytesToConsume) throws IOException {
if (this.recordDelimiterBytes != null) {
return readCustomLine(str, maxLineLength, maxBytesToConsume);
} else {
return readDefaultLine(str, maxLineLength, maxBytesToConsume);
}
}它裡面呼叫了readCustomLine方法和readDefaultLine方法，下面看看這兩個方法
private int readCustomLine(Text str, int maxLineLength, int maxBytesToConsume)
throws IOException {
str.clear();
int txtLength = 0; // tracks str.getLength(), as an optimization
long bytesConsumed = 0;
int delPosn = 0;
int ambiguousByteCount=0; // To capture the ambiguous characters count
do {
int startPosn = bufferPosn; // Start from previous end position
if (bufferPosn >= bufferLength) {
startPosn = bufferPosn = 0;
bufferLength = fillBuffer(in, buffer, ambiguousByteCount > 0);
if (bufferLength <= 0) {
if (ambiguousByteCount > 0) {
str.append(recordDelimiterBytes, 0, ambiguousByteCount);
bytesConsumed += ambiguousByteCount;
}
break; // EOF
}
}
for (; bufferPosn < bufferLength; ++bufferPosn) {
if (buffer[bufferPosn] == recordDelimiterBytes[delPosn]) {
delPosn++;
if (delPosn >= recordDelimiterBytes.length) {
bufferPosn++;
break;
}
} else if (delPosn != 0) {
bufferPosn--;
delPosn = 0;
}
}
int readLength = bufferPosn - startPosn;
bytesConsumed += readLength;
int appendLength = readLength - delPosn;
if (appendLength > maxLineLength - txtLength) {
appendLength = maxLineLength - txtLength;
}
bytesConsumed += ambiguousByteCount;
if (appendLength >= 0 && ambiguousByteCount > 0) {
//appending the ambiguous characters (refer case 2.2)
str.append(recordDelimiterBytes, 0, ambiguousByteCount);
ambiguousByteCount = 0;
// since it is now certain that the split did not split a delimiter we
// should not read the next record: clear the flag otherwise duplicate
// records could be generated
unsetNeedAdditionalRecordAfterSplit();
}
if (appendLength > 0) {
str.append(buffer, startPosn, appendLength);
txtLength += appendLength;
}
if (bufferPosn >= bufferLength) {
if (delPosn > 0 && delPosn < recordDelimiterBytes.length) {
ambiguousByteCount = delPosn;
bytesConsumed -= ambiguousByteCount; //to be consumed in next
}
}
} while (delPosn < recordDelimiterBytes.length
&& bytesConsumed < maxBytesToConsume);
if (bytesConsumed > Integer.MAX_VALUE) {
throw new IOException("Too many bytes before delimiter: " + bytesConsumed);
}
return (int) bytesConsumed;
} private int readDefaultLine(Text str, int maxLineLength, int maxBytesToConsume)
throws IOException {
str.clear();
int txtLength = 0; //tracks str.getLength(), as an optimization
int newlineLength = 0; //length of terminating newline
boolean prevCharCR = false; //true of prev char was CR
long bytesConsumed = 0;
do {
int startPosn = bufferPosn; //starting from where we left off the last time
if (bufferPosn >= bufferLength) {
startPosn = bufferPosn = 0;
if (prevCharCR) {
++bytesConsumed; //account for CR from previous read
}
bufferLength = fillBuffer(in, buffer, prevCharCR);
if (bufferLength <= 0) {
break; // EOF
}
}
for (; bufferPosn < bufferLength; ++bufferPosn) { //search for newline
if (buffer[bufferPosn] == LF) {
newlineLength = (prevCharCR) ? 2 : 1;
++bufferPosn; // at next invocation proceed from following byte
break;
}
if (prevCharCR) { //CR + notLF, we are at notLF
newlineLength = 1;
break;
}
prevCharCR = (buffer[bufferPosn] == CR);
}
int readLength = bufferPosn - startPosn;
if (prevCharCR && newlineLength == 0) {
--readLength; //CR at the end of the buffer
}
bytesConsumed += readLength;
int appendLength = readLength - newlineLength;
if (appendLength > maxLineLength - txtLength) {
appendLength = maxLineLength - txtLength;
}
if (appendLength > 0) {
str.append(buffer, startPosn, appendLength);
txtLength += appendLength;
}
} while (newlineLength == 0 && bytesConsumed < maxBytesToConsume);
if (bytesConsumed > Integer.MAX_VALUE) {
throw new IOException("Too many bytes before newline: " + bytesConsumed);
}
return (int)bytesConsumed;
}注意注意readCustomLine和readDefaultLine方法的第一句都用了一句程式碼（重點，後面我們自定義時要改的地方）
他們都用了str.clear();
這句程式碼什麼意思，意思是系統每讀完一行，它會清空這一行的值！！！
如果我們自定義讀取多行的時候，肯定不能清空它，因為我們需要它來計數第二行的位置
比如
123，
456
789，
111
如果一次讀兩行的話 假如我把第一行清空了，那麼我第二行的偏移量就得不到正確的值了，讀出來的值本應該是
123，456
789，111
但是如果清空了的話 就讀出來少了一行
變成了
456
111
所以我們只有獨到最後一行才清空值，它前面的行都不能清空
這就要求我們到時候自己過載一個方法了，到時候再說，大家接著看
有沒有暈了，沒有？ 那就好，我都說得這麼清楚了，還暈的話，大家就先休息一下
我幫大家理一理：看都用到了哪些類
最開始TextInputFormat裡面用到了LineRecordReader，LineRecordReader裡面用到了SplitLineReader，而SplitLineReader裡面用到了LineReader
自定義的時候思路按這個來
TextInputFormat–》LineRecordReader–》SplitLineReader–》LineReader
下面寫第一個自定義的TextInputFormat
package com.my.input;
import java.io.IOException;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.CompressionCodecFactory;
import org.apache.hadoop.io.compress.SplittableCompressionCodec;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
public class myInputFormat extends FileInputFormat<Text,Text> {
//用來壓縮的
@Override
protected boolean isSplitable(JobContext context, Path file) {
final CompressionCodec codec =
new CompressionCodecFactory(context.getConfiguration()).getCodec(file);
if (null == codec) {
return true;
}
return codec instanceof SplittableCompressionCodec;
}
@Override
public RecordReader<Text, Text> createRecordReader(InputSplit genericSplit, TaskAttemptContext context)
throws IOException, InterruptedException {
context.setStatus(genericSplit.toString());
return new MyRecordReader(context.getConfiguration());
}
}接著寫一個自定義的LineRecordReader
其中修改了182行開始的以下程式碼
因為我這裡要實現輸出多行，所以寫了一個for迴圈,又由於我前面說得前面的行不能清空，所以要加一個boolean標誌量
把
while (getFilePosition() <= end || in.needAdditionalRecordAfterSplit()) {
if (pos == 0) {
newSize = skipUtfByteOrderMark();
} else {
newSize = in.readLine(value, maxLineLength, maxBytesToConsume(pos));
pos += newSize;
}
if ((newSize == 0) || (newSize < maxLineLength)) {
break;
}
// line too long. try again
LOG.info("Skipped line of size " + newSize + " at pos " +
(pos - newSize));
}改為
boolean clear = true;
for (int i = 1; i <= 2; i++) {
if (i == 2) {
clear = false;
}
while (getFilePosition() <= end || in.needAdditionalRecordAfterSplit()) {
if (pos == 0) {
newSize = skipUtfByteOrderMark();
} else {
newSize = in.readLine(value, maxLineLength, maxBytesToConsume(pos), clear);
pos += newSize;
}
if ((newSize == 0) || (newSize < maxLineLength)) {
break;
}
// line too long. try again
LOG.info("Skipped line of size " + newSize + " at pos " + (pos - newSize));
}
}再寫自定義SplitLineReader
package com.my.lingRecordReader;
import java.io.IOException;
import java.io.InputStream;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class MySplitLineReader extends MyLineReader {
public MySplitLineReader(InputStream in, byte[] recordDelimiterBytes) {
super(in, recordDelimiterBytes);
}
public MySplitLineReader(InputStream in, Configuration conf,
byte[] recordDelimiterBytes) throws IOException {
super(in, conf, recordDelimiterBytes);
}
public boolean needAdditionalRecordAfterSplit() {
return false;
}
}最後寫自定義LineReader
它過載了一個readLine(Text str, int maxLineLength, int maxBytesToConsume, boolean clear)方法來實現不清空前面讀取的行的值
package com.my.lingRecordReader;
/**
* 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.
*/
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Text;
/**
* A class that provides a line reader from an input stream. Depending on the
* constructor used, lines will either be terminated by:
* <ul>
* <li>one of the following: '\n' (LF) , '\r' (CR), or '\r\n' (CR+LF).</li>
* <li><em>or</em>, a custom byte sequence delimiter</li>
* </ul>
* In both cases, EOF also terminates an otherwise unterminated line.
*/
@InterfaceAudience.LimitedPrivate({ "MapReduce" })
@InterfaceStability.Unstable
public class MyLineReader implements Closeable {
private static final int DEFAULT_BUFFER_SIZE = 64 * 1024;
private int bufferSize = DEFAULT_BUFFER_SIZE;
private InputStream in;
private byte[] buffer;
// the number of bytes of real data in the buffer
private int bufferLength = 0;
// the current position in the buffer
private