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 org.apache.hadoop.mapred; import java.io.IOException; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.io.LongWritable; import org.apache.hadoop.io.Text; /** * This class treats a line in the input as a key/value pair separated by a * separator character. The separator can be specified in config file * under the attribute name mapreduce.input.keyvaluelinerecordreader.key.value.separator. The default * separator is the tab character ('\t'). */ @InterfaceAudience.Public @InterfaceStability.Stable public class KeyValueLineRecordReader implements RecordReader<Text, Text> { private final LineRecordReader lineRecordReader; private byte separator = (byte) '\t'; private LongWritable dummyKey; private Text innerValue; public Class getKeyClass() { return Text.class; } public Text createKey() { return new Text(); } public Text createValue() { return new Text(); } public KeyValueLineRecordReader(Configuration job, FileSplit split) throws IOException { lineRecordReader = new LineRecordReader(job, split); dummyKey = lineRecordReader.createKey(); innerValue = lineRecordReader.createValue(); String sepStr = job.get("mapreduce.input.keyvaluelinerecordreader.key.value.separator", "\t"); this.separator = (byte) sepStr.charAt(0); } public static int findSeparator(byte[] utf, int start, int length, byte sep) { return org.apache.hadoop.mapreduce.lib.input.KeyValueLineRecordReader.findSeparator(utf, start, length, sep); } /** Read key/value pair in a line. */ public synchronized boolean next(Text key, Text value) throws IOException { byte[] line = null; int lineLen = -1; if (lineRecordReader.next(dummyKey, innerValue)) { line = innerValue.getBytes(); lineLen = innerValue.getLength(); } else { return false; } if (line == null) return false; int pos = findSeparator(line, 0, lineLen, this.separator); org.apache.hadoop.mapreduce.lib.input.KeyValueLineRecordReader.setKeyValue(key, value, line, lineLen, pos); return true; } public float getProgress() throws IOException { return lineRecordReader.getProgress(); } public synchronized long getPos() throws IOException { return lineRecordReader.getPos(); } public synchronized void close() throws IOException { lineRecordReader.close(); } }