?? textinputformat.java
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/** * Copyright 2005 The Apache Software Foundation * * Licensed 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 org.apache.hadoop.mapred;import java.io.IOException;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.FSDataInputStream;import org.apache.hadoop.io.Writable;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.UTF8;/** An {@link InputFormat} for plain text files. Files are broken into lines. * Either linefeed or carriage-return are used to signal end of line. Keys are * the position in the file, and values are the line of text.. */public class TextInputFormat extends InputFormatBase { public RecordReader getRecordReader(FileSystem fs, FileSplit split, JobConf job, Reporter reporter) throws IOException { reporter.setStatus(split.toString()); final long start = split.getStart(); final long end = start + split.getLength(); // open the file and seek to the start of the split final FSDataInputStream in = fs.open(split.getFile()); if (start != 0) { in.seek(start-1); while (in.getPos() < end) { // scan to the next newline in the file char c = (char)in.read(); if (c == '\r' || c == '\n') { break; } } } return new RecordReader() { /** Read a line. */ public synchronized boolean next(Writable key, Writable value) throws IOException { long pos = in.getPos(); if (pos >= end) return false; ((LongWritable)key).set(pos); // key is position ((UTF8)value).set(readLine(in)); // value is line return true; } public synchronized long getPos() throws IOException { return in.getPos(); } public synchronized void close() throws IOException { in.close(); } }; } private static String readLine(FSDataInputStream in) throws IOException { StringBuffer buffer = new StringBuffer(); while (true) { int b = in.read(); if (b == -1) break; char c = (char)b; // bug: this assumes eight-bit characters. if (c == '\r' || c == '\n') break; buffer.append(c); } return buffer.toString(); }}
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