Hadoop版Helloworld之wordcount运行示例

时间：2022-05-21 20:50:52

1.编写一个统计单词数量的java程序，并命名为wordcount.java，代码如下：

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.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 {

  public static class TokenizerMapper

       extends Mapper<Object, Text, Text, IntWritable>{

    private final static IntWritable one = new IntWritable(1);

    private Text word = new Text();

    public void map(Object key, Text value, Context context

                    ) throws IOException, InterruptedException {

      StringTokenizer itr = new StringTokenizer(value.toString());

      while (itr.hasMoreTokens()) {

        word.set(itr.nextToken());

        context.write(word, one);

      }

    }

  }

  public static class IntSumReducer

       extends Reducer<Text,IntWritable,Text,IntWritable> {

    private IntWritable result = new IntWritable();

    public void reduce(Text key, Iterable<IntWritable> values,

                       Context context

                       ) throws IOException, InterruptedException {

      int sum = 0;

      for (IntWritable val : values) {

        sum += val.get();

      }

      result.set(sum);

      context.write(key, result);

    }

  }

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

    Configuration conf = new Configuration();

    Job job = Job.getInstance(conf, "word count");

    job.setJarByClass(WordCount.class);

    job.setMapperClass(TokenizerMapper.class);

    job.setCombinerClass(IntSumReducer.class);

    job.setReducerClass(IntSumReducer.class);

    job.setOutputKeyClass(Text.class);

    job.setOutputValueClass(IntWritable.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));

    FileOutputFormat.setOutputPath(job, new Path(args[1]));

    System.exit(job.waitForCompletion(true) ? 0 : 1);

  }

}

2.声明java环境变量：

export JAVA_HOME=/usr/java/default

export PATH=${JAVA_HOME}/bin:${PATH}

export HADOOP_CLASSPATH=${JAVA_HOME}/lib/tools.jar

其中JAVA_HOME根据自己安装java的实际路径进行配置。

注意：如果不声明以上环境变量，那么在以后运行时，将会收到错误提示：

Hadoop版Helloworld之wordcount运行示例

3.编译并创建jar包。

bin/hadoop com.sun.tools.javac.Main WordCount.java

jar cf wc.jar WordCount*.class

4.运行第三步骤生成的wc.jar包。此时要注意，output文件夹不要手工创建，系统运行后会自动创建。

bin/hadoop jar wc.jar WordCount /user/root/wordcount/input /user/root/wordcount/output

正常运行结束后，会在outPut文件夹下生成part-r-00000及__SUCCESS两个文件，其中part-r-00000存储分析结果。运行命令：

bin/hadoop fs -cat /user/root/wordcount/output/part-r-00000

即可查看分析结果，如下图所示：
Hadoop版Helloworld之wordcount运行示例

至此，本示例完成。

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