Shulou(Shulou.com)06/01 Report--

This article introduces the knowledge of "how to set delimiters in TopKey". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

The default delimiter for key and value is the tab key

Set delimiter

Program one

Package org.conan.myhadoop.TopKey;import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat / / single file maximum value public class TopKMapReduce {static class TopKMapper extends Mapper {/ / output key private Text mapOutputKey = new Text (); / / output value private LongWritable mapOutputValue = new LongWritable (); / / store maximum and initial values long topkValue = Long.MIN_VALUE @ Override protected void map (LongWritable key, Text value, Context context) throws IOException, InterruptedException {String lineValue = value.toString (); String [] strs = lineValue.split ("\ t"); / / median long tempValue = Long.valueOf (strs [1]); if (topkValue)

< tempValue) { topkValue = tempValue; mapOutputKey.set(strs[0]); } } @Override protected void cleanup(Context context) throws IOException, InterruptedException { mapOutputValue.set(topkValue); context.write(mapOutputKey, mapOutputValue); } @Override protected void setup(Context context) throws IOException, InterruptedException { super.setup(context); } } public int run(String[] args) throws Exception { Configuration conf = new Configuration(); Job job = new Job(conf, TopKMapReduce.class.getSimpleName()); job.setJarByClass(TopKMapReduce.class); Path inputDir = new Path(args[0]); FileInputFormat.addInputPath(job, inputDir); job.setInputFormatClass(TextInputFormat.class); job.setMapperClass(TopKMapper.class); job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(LongWritable.class); // job.setReducerClass(ModuleReducer.class); // job.setOutputKeyClass(LongWritable.class); // job.setOutputValueClass(Text.class); job.setNumReduceTasks(0); Path outputDir = new Path(args[1]); FileOutputFormat.setOutputPath(job, outputDir); Boolean isCompletion = job.waitForCompletion(true); return isCompletion ? 0 : 1; } public static void main(String[] args) throws Exception { args = new String[] { "hdfs://hadoop-master:9000/data/wcoutput", "hdfs://hadoop-master:9000/data/topkoutput" }; int status = new TopKMapReduce().run(args); System.exit(status); }} 程序二 package org.conan.myhadoop.TopKey;import java.io.IOException;import java.util.Set;import java.util.TreeMap;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;//单文件 top n TreeMap实现public class TopKMapReduceV2 { static class TopKMapper extends Mapper { public static final int K=3;//前三名 private LongWritable mapKey = new LongWritable(); private Text mapValue = new Text(); TreeMap topMap = null;//默认按key的升序排列 @Override protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { String lineValue = value.toString(); String[] strs = lineValue.split("\t"); long tempValue = Long.valueOf(strs[1]); String tempKey=strs[0]; mapKey.set(tempValue); mapValue.set(tempKey); topMap.put(mapKey, mapValue); if(topMap.size()>

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