第7章的代码-林子雨编著《大数据基础编程、实验和案例教程（第3版）》教材

林子雨编著《大数据基础编程、实验和案例教程（第3版）》(教材官网)教材中的命令行和代码，在纸质教材中的印刷效果不是很好，可能会影响读者对命令行和代码的理解，为了方便读者正确理解命令行和代码或者直接拷贝命令行和代码用于上机实验，这里提供全书配套的所有命令行和代码。
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第7章 MapReduce基础编程

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教材第107页

import java.io.IOException;
import java.util.Iterator;
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.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.GenericOptionsParser;
public class WordCount {
    public WordCount() {
    }
     public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        String[] otherArgs = (new GenericOptionsParser(conf, args)).getRemainingArgs();
        if(otherArgs.length < 2) {
            System.err.println("Usage: wordcount <in> [<in>...] <out>");
            System.exit(2);
        }
        Job job = Job.getInstance(conf, "word count");
        job.setJarByClass(WordCount.class);
        job.setMapperClass(WordCount.TokenizerMapper.class);
        job.setCombinerClass(WordCount.IntSumReducer.class);
        job.setReducerClass(WordCount.IntSumReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class); 
        for(int i = 0; i < otherArgs.length - 1; ++i) {
            FileInputFormat.addInputPath(job, new Path(otherArgs[i]));
        }
        FileOutputFormat.setOutputPath(job, new Path(otherArgs[otherArgs.length - 1]));
        System.exit(job.waitForCompletion(true)?0:1);
    }
    public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable> {
        private static final IntWritable one = new IntWritable(1);
        private Text word = new Text();
        public TokenizerMapper() {
        }
        public void map(Object key, Text value, Mapper<Object, Text, Text, IntWritable>.Context context) throws IOException, InterruptedException {
            StringTokenizer itr = new StringTokenizer(value.toString()); 
            while(itr.hasMoreTokens()) {
                this.word.set(itr.nextToken());
                context.write(this.word, one);
            }
        }
    }
public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
        private IntWritable result = new IntWritable();
        public IntSumReducer() {
        }
        public void reduce(Text key, Iterable<IntWritable> values, Reducer<Text, IntWritable, Text, IntWritable>.Context context) throws IOException, InterruptedException {
            int sum = 0;
            IntWritable val;
            for(Iterator i$ = values.iterator(); i$.hasNext(); sum += val.get()) {
                val = (IntWritable)i$.next();
            }
            this.result.set(sum);
            context.write(key, this.result);
        }
    }
}

教材第109页

cd /usr/local/hadoop

$export CLASSPATH="/usr/local/hadoop/share/hadoop/common/hadoop-common-3.3.5.jar:/usr/local/hadoop/share/hadoop/mapreduce/hadoop-mapreduce-client-core-3.3.5.jar:/usr/local/hadoop/share/hadoop/common/lib/commons-cli-1.2.jar:$CLASSPATH"

javac WordCount.java

jar -cvf WordCount.jar *.class

./bin/hadoop jar WordCount.jar WordCount input output

./bin/hadoop fs -cat output/*

教材第117页

cd /usr/local/hadoop/myapp
ls

教材第118页

cd /usr/local/hadoop
./sbin/start-dfs.sh

cd /usr/local/hadoop
./bin/hdfs dfs -rm -r input
./bin/hdfs dfs -rm -r output

cd /usr/local/hadoop
./bin/hdfs dfs -mkdir input

cd /usr/local/hadoop
./bin/hdfs dfs -put ./wordfile1.txt input
./bin/hdfs dfs -put ./wordfile2.txt input

cd /usr/local/hadoop
./bin/hdfs dfs -rm -r /user/hadoop/output

cd /usr/local/hadoop
./bin/hadoop jar ./myapp/WordCount.jar input output

教材第119页

cd /usr/local/hadoop
./bin/hdfs dfs -cat output/*