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.hn.cluster.hadoop.mrs; import java.io.DataInput; import java.io.DataOutput; import java.io.IOException; import java.util.StringTokenizer; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.IntWritable; import org.apache.hadoop.io.LongWritable; import org.apache.hadoop.io.RawComparator; import org.apache.hadoop.io.Text; import org.apache.hadoop.io.WritableComparable; import org.apache.hadoop.io.WritableComparator; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.input.LineRecordReader; import org.apache.hadoop.mapreduce.lib.input.TextInputFormat; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.Mapper; import org.apache.hadoop.mapreduce.Partitioner; import org.apache.hadoop.mapreduce.Reducer; /** * This is an example Hadoop Map/Reduce application. It reads the text input * files that must contain two integers per a line. The output is sorted by the * first and second number and grouped on the first number. * * * key?MapRduce??MapMerge * * MR? WritableComparableRawComparator? * writableComparable????????? * RawComparator???????????? * ?compareToKey?Hadoop???? * HadoopcompareTokey????mapreduce * mapmapreducereduce?compareTo???? * ?? * * To run: bin/hadoop jar build/hadoop-examples.jar secondarysort <i>in-dir</i> * <i>out-dir</i> */ public class SecondarySort { /** * Define a pair of integers that are writable. They are serialized in a * byte comparable format. */ public static class IntPair implements WritableComparable<IntPair> { private int first = 0; private int second = 0; /** * Set the left and right values. */ public void set(int left, int right) { first = left; second = right; } public int getFirst() { return first; } public int getSecond() { return second; } /** * Read the two integers. Encoded as: MIN_VALUE -> 0, 0 -> -MIN_VALUE, * MAX_VALUE-> -1 */ @Override public void readFields(DataInput in) throws IOException { first = in.readInt() + Integer.MIN_VALUE; second = in.readInt() + Integer.MIN_VALUE; } @Override public void write(DataOutput out) throws IOException { out.writeInt(first - Integer.MIN_VALUE); out.writeInt(second - Integer.MIN_VALUE); } @Override public int hashCode() { return first * 157 + second; } @Override public boolean equals(Object right) { if (right instanceof IntPair) { IntPair r = (IntPair) right; return r.first == first && r.second == second; } else { return false; } } /** A Comparator that compares serialized IntPair. */ public static class Comparator extends WritableComparator { public Comparator() { super(IntPair.class); } public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) { return compareBytes(b1, s1, l1, b2, s2, l2); } } static { // register this comparator WritableComparator.define(IntPair.class, new Comparator()); } @Override public int compareTo(IntPair o) { if (first != o.first) { return first < o.first ? -1 : 1; } else if (second != o.second) { return second < o.second ? -1 : 1; } else { return 0; } } } /** * Partition based on the first part of the pair. * map?key???reduce???? * HadoopHash Partitioner * ??Partition?? * ?123? ??;1 ?;2 ;3 ;4 ;1 ?;3 ;11 * ??Partition * ??3reduce?3 * partition????hash?? */ public static class FirstPartitioner extends Partitioner<IntPair, IntWritable> { /** * getPartition()0Reducerint?<key,value>?Reducer */ @Override public int getPartition(IntPair key, IntWritable value, int numPartitions) { return Math.abs(key.getFirst() * 127) % numPartitions; } } /** * Compare only the first part of the pair, so that reduce is called once * for each value of the first part. */ public static class FirstGroupingComparator implements RawComparator<IntPair> { @Override public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) { return WritableComparator.compareBytes(b1, s1, Integer.SIZE / 8, b2, s2, Integer.SIZE / 8); } @Override public int compare(IntPair o1, IntPair o2) { int l = o1.getFirst(); int r = o2.getFirst(); return l == r ? 0 : (l < r ? -1 : 1); } } /** * Read two integers from each line and generate a key, value pair as * ((left, right), right). */ public static class MapClass extends Mapper<LongWritable, Text, IntPair, IntWritable> { private final IntPair key = new IntPair(); private final IntWritable value = new IntWritable(); /** * map a#1 1 z#3 3 b#2 2 a#100 100 a#3 3 b#1 1 */ @Override public void map(LongWritable inKey, Text inValue, Context context) throws IOException, InterruptedException { StringTokenizer itr = new StringTokenizer(inValue.toString()); int left = 0; int right = 0; if (itr.hasMoreTokens()) { left = Integer.parseInt(itr.nextToken()); if (itr.hasMoreTokens()) { right = Integer.parseInt(itr.nextToken()); } key.set(left, right); value.set(right); context.write(key, value); } } } public static class Reduce extends Reducer<IntPair, IntWritable, Text, IntWritable> { private static final Text SEPARATOR = new Text("------------------------------------------------"); private final Text first = new Text(); @Override public void reduce(IntPair key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { context.write(SEPARATOR, null); first.set(Integer.toString(key.getFirst())); for (IntWritable value : values) { context.write(first, value); } } } public static void main(String[] args) throws Exception { // ?hadoop? Configuration conf = new Configuration(); // ? Job job = new Job(conf, "secondary sort"); job.setJarByClass(SecondarySort.class); // Mapper job.setMapperClass(MapClass.class); // Reducer job.setReducerClass(Reduce.class); // job.setPartitionerClass(FirstPartitioner.class); // job.setGroupingComparatorClass(FirstGroupingComparator.class); // map Key job.setMapOutputKeyClass(IntPair.class); // mapValue job.setMapOutputValueClass(IntWritable.class); // rduceKeyTextOutputFormatClassTextOutputFormat job.setOutputKeyClass(Text.class); // rduceValue job.setOutputValueClass(IntWritable.class); /** * ?????splites???RecordReder * ??RecordReder?keyvalue * Map<LongWritable, Text> * Mapmap<LongWritable, Text>Mapmap * ?List<IntPair, IntWritable> * map?job.setPartitionerClassList?reducer */ job.setInputFormatClass(TextInputFormat.class); // ??RecordWriter? job.setOutputFormatClass(TextOutputFormat.class); // hdfs FileInputFormat.addInputPath(job, new Path("hdfs://192.1168.1.12:9000/input/input/soso.txt")); // hdfs FileOutputFormat.setOutputPath(job, new Path("hdfs://192.1168.1.12:9000/output/sort/")); // ??job System.exit(job.waitForCompletion(true) ? 0 : 1); } }