编写WordCount程序之一固定格式讲解

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WordCount因果图

MapReduce中 map和reduce函数格式

MapReduce中，map和reduce函数遵循如下常规格式：

代码语言：javascript复制

map: (K1, V1) → list(K2, V2)
reduce: (K2, list(V2)) → list(K3, V3)

Mapper的基类：

代码语言：javascript复制

protected void map(KEY key, VALUE value, 
    Context context) throws     IOException, InterruptedException {   
 }

Reducer的基类：

代码语言：javascript复制

protected void reduce(KEY key, Iterable<VALUE> values,
     Context context) throws IOException, InterruptedException { 
 }

Context是上下文对象

代码模板

wordcount 代码

代码编写依据，也就是固定写法 input–>map—>reduce->output 以下java代码实现此命令的功能bin/hdfs dfs jar share/hadoop/mapreduce/hadoop-mapreduce-examples-2.5.0.jar input output

代码语言：javascript复制

package com.lizh.hadoop.mapreduce;

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
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.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class WordCount {

    private static Log logger = LogFactory.getLog(WordCount.class);
    //step1 Mapper class
    
    public static class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable>{
        private Text mapoutputKey = new Text();
        private static final IntWritable mapOutputValues =  new IntWritable(1);//全局只有一个
        @Override
        protected void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            // TODO Auto-generated method stubl
            
            
            String linevalue = value.toString();
            StringTokenizer stringTokenizer = new StringTokenizer(linevalue);
            while(stringTokenizer.hasMoreTokens()){
                String workvalue = stringTokenizer.nextToken();
                mapoutputKey.set(workvalue);
                context.write(mapoutputKey, mapOutputValues);
                logger.info("-----WordCountMapper-----" mapOutputValues.get());
            }
        }
        
    }
    
    //step2 Reduce class
    public static class WordCountReduces extends Reducer<Text, IntWritable, Text, IntWritable>{

        private IntWritable reduceOutputValues =  new IntWritable();
        
        @Override
        protected void reduce(Text key, Iterable<IntWritable> vaues,Context context)
                throws IOException, InterruptedException {
            int sum =0;
            for(IntWritable iv:vaues){
                sum=sum iv.get();
            }
            reduceOutputValues.set(sum);
            context.write(key, reduceOutputValues);
        }
        
    }
    
    //step3 driver component job 
    
    public int run(String[] args) throws Exception{
        //1 get configration file core-site.xml hdfs-site.xml 
        Configuration configuration = new Configuration();
        
        //2 create job
        Job job = Job.getInstance(configuration, this.getClass().getSimpleName());
        //3 run jar
        job.setJarByClass(this.getClass());
        
        //4 set job
        //input-->map--->reduce-->output
        //4.1 input
        Path path = new Path(args[0]);
        FileInputFormat.addInputPath(job, path);
        
        //4.2 map
        job.setMapperClass(WordCountMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        
        //4.3 reduce
        job.setReducerClass(WordCountReduces.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        
        //4.4 output
        Path outputpath = new Path(args[1]);
        FileOutputFormat.setOutputPath(job, outputpath);
        
        //5 submit job
        boolean rv = job.waitForCompletion(true);
        
        return rv ? 0:1;
        
    }
    
    public static void main(String[] args) throws Exception{
        
        int rv = new WordCount().run(args);
        System.exit(rv);
    }
}

map类业务处理

map 业务处理逻辑 ————–input——– <0,hadoop yarn> ————–处理——— hadoop yarn –>split->hadoop,yarn ————-output——- <hadoop,1> <yarn,1>

代码语言：javascript复制

public static class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable>{
        private Text mapoutputKey = new Text();
        //全局只有一个
        private static final IntWritable mapOutputValues =  new IntWritable(1);
        @Override
        protected void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            // TODO Auto-generated method stubl
            
            
            String linevalue = value.toString();
            StringTokenizer stringTokenizer = new StringTokenizer(linevalue);
            while(stringTokenizer.hasMoreTokens()){
                String workvalue = stringTokenizer.nextToken();
                mapoutputKey.set(workvalue);
                context.write(mapoutputKey, mapOutputValues);
                logger.info("-----WordCountMapper-----" mapOutputValues.get());
            }
        }
        
    }

reduce类业务处理过程

reduce 业务处理过程 map–>shuffle–>mapreduce

代码语言：javascript复制

------------input（map的输出结果）-----------------
<hadoop,1>
<hadoop,1>
<hadoop,1>
----------------分组----------------
将相同key的值合并到一起，放到一个集合
<hadoop,1>
<hadoop,1>    ->  <hadoop,list(1,1,1)>
<hadoop,1>

代码语言：javascript复制

    //step2 Reduce class
    public static class WordCountReduces extends Reducer<Text, IntWritable, Text, IntWritable>{

        private IntWritable reduceOutputValues =  new IntWritable();
        
        @Override
        protected void reduce(Text key, Iterable<IntWritable> vaues,Context context)
                throws IOException, InterruptedException {
            int sum =0;
            for(IntWritable iv:vaues){
                sum=sum iv.get();
            }
            reduceOutputValues.set(sum);
            context.write(key, reduceOutputValues);
        }
        
    }

优化MapReduce写法

mapReduce 继承configured类， 并实现 Tool接口 tool接口类中的run方法重写 configured 提供初始化工作。

代码语言：javascript复制

package com.lizh.hadoop.mapreduce;

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class WordCountMapReduce extends Configured implements Tool {

    private static Log logger = LogFactory.getLog(WordCountMapReduce.class);
    //step1 Mapper class
    
    public static class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable>{
        private Text mapoutputKey = new Text();
        private static final IntWritable mapOutputValues =  new IntWritable(1);//全局只有一个
        @Override
        protected void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            // TODO Auto-generated method stubl
            
            
            String linevalue = value.toString();
            StringTokenizer stringTokenizer = new StringTokenizer(linevalue);
            while(stringTokenizer.hasMoreTokens()){
                String workvalue = stringTokenizer.nextToken();
                mapoutputKey.set(workvalue);
                context.write(mapoutputKey, mapOutputValues);
                logger.info("-----WordCountMapper-----" mapOutputValues.get());
            }
        }
        
    }
    
    //step2 Reduce class
    public static class WordCountReduces extends Reducer<Text, IntWritable, Text, IntWritable>{

        private IntWritable reduceOutputValues =  new IntWritable();
        
        @Override
        protected void reduce(Text key, Iterable<IntWritable> vaues,Context context)
                throws IOException, InterruptedException {
            int sum =0;
            for(IntWritable iv:vaues){
                sum=sum iv.get();
            }
            reduceOutputValues.set(sum);
            context.write(key, reduceOutputValues);
        }
        
    }
    
    //step3 driver component job 
    
    public int run(String[] args) throws Exception{
        //1 get configration file core-site.xml hdfs-site.xml 
        Configuration configuration = super.getConf();//优化
        
        //2 create job
        Job job = Job.getInstance(configuration, this.getClass().getSimpleName());
        //3 run jar
        job.setJarByClass(this.getClass());
        
        //4 set job
        //input-->map--->reduce-->output
        //4.1 input
        Path path = new Path(args[0]);
        FileInputFormat.addInputPath(job, path);
        
        //4.2 map
        job.setMapperClass(WordCountMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        
        //4.3 reduce
        job.setReducerClass(WordCountReduces.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        
        //4.4 output
        Path outputpath = new Path(args[1]);
        FileOutputFormat.setOutputPath(job, outputpath);
        
        //5 submit job
        boolean rv = job.waitForCompletion(true);//true的时候打印日志
        
        return rv ? 0:1;
        
    }
    
    public static void main(String[] args) throws Exception{
        
        //int rv = new WordCountMapReduce().run(args);
        Configuration configuration = new Configuration();
        //使用工具类运行
        int rv  = ToolRunner.run(configuration, new WordCountMapReduce(), args);
        System.exit(rv);
    }
}

抽象出模板

代码语言：javascript复制

package org.apache.hadoop.mapreduce;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class WordCountMapReduce extends Configured implements Tool {

    /**
     * Mapper Class : public class Mapper<KEYIN, VALUEIN, KEYOUT, VALUEOUT>
     * 
     * @param args
     */
    public static class WordCountMapper extends //
            Mapper<LongWritable, Text, Text, LongWritable> {

        private Text mapOutputKey = new Text();
        private LongWritable mapOutputValue = new LongWritable(1);

        @Override
        protected void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            
        }
    }

    /**
     * Reducer Class : public class Reducer<KEYIN,VALUEIN,KEYOUT,VALUEOUT>
     * 
     * @param args
     */
    public static class WordCountReducer extends //
            Reducer<Text, LongWritable, Text, LongWritable> {

        private LongWritable outputValue = new LongWritable();

        @Override
        protected void reduce(Text key, Iterable<LongWritable> values,
                Context context) throws IOException, InterruptedException {
            // temp sum
            
        }
    }

    /**
     * Driver : Createsetsubmit Job
     * 
     * @param args
     * @throws Exception
     */
    public int run(String[] args) throws Exception {
        // 1.Get Configuration
        Configuration conf = super.getConf();

        // 2.Create Job
        Job job = Job.getInstance(conf);
        job.setJarByClass(getClass());

        // 3.Set Job
        // Input --> map --> reduce --> output
        // 3.1 Input
        Path inPath = new Path(args[0]);
        FileInputFormat.addInputPath(job, inPath);

        // 3.2 Map class
        job.setMapperClass(WordCountMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);

        // 3.3 Reduce class
        job.setReducerClass(WordCountReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongWritable.class);

        // 3.4 Output
        Path outPath = new Path(args[1]);

        FileSystem dfs = FileSystem.get(conf);
        if (dfs.exists(outPath)) {
            dfs.delete(outPath, true);
        }

        FileOutputFormat.setOutputPath(job, outPath);

        // 4.Submit Job
        boolean isSuccess = job.waitForCompletion(true);
        return isSuccess ? 0 : 1;
    }

    public static void main(String[] args) throws Exception {
        

        Configuration conf = new Configuration();
    
        
        // run job
        int status = ToolRunner.run(//
                conf,//
                new WordCountMapReduce(),//
                args);

        // exit program
        System.exit(status);
    }
}

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