Mac在hadoop3.1.1上运行WordCount例子

搭建好了Hadoop以后，用一个大家都常用的WordCount例子来试一试。

下面是WordCount的代码：

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);
  }
}

选择一个目录下，使用vim WordCount.java，将上面的代码复制进去。 

然后用以下的命令编译WordCount.java文件

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

 编译成功以后，同目录下会出现三个文件

WordCount$IntSumReducer.class 

WordCount$TokenizerMapper.class 

WordCount.class

之后，用以下的命令把文件打包为jar格式

jar cf wc.jar WordCount*.class

在hdfs的根目录下新建一个目录wordcount，方便管理。目录名是可以改的

hdfs dfs -mkdir /wordcount

然后新建一个要用来分析的文件，vim  helloworld.data, 在里面输入数据。 

I love chongqing

I love china

接着，用以下命令将helloworld.data文件上传到hdfs的wordcount目录中 

hdfs dfs -put helloworld.data /wordcount

启动hdfs和yarn，然后运行程序，运行的结果会自动生成一个叫做part-r-00000的文件。

hadoop jar wc.jar WordCount /wordcount /wordcount/output

这个过程没有问题的话，在/wordcount目录下就会出现一个output目录。我们进入该目录查看part-r-00000文件的结果就好了。

hdfs dfs -cat /wordcount/output/part-r-00000

下面就是文件里面打印出来的内容。 可以啦。

 

参考连接：https://blog.youkuaiyun.com/litianxiang_kaola/article/details/71154302

                  https://blog.youkuaiyun.com/u010223750/article/details/52838186