hdfs单词统计java源码

下面是一个简单的Hadoop MapReduce程序，用于对HDFS中的文本文件进行单词计数：

1.创建一个Java类WordCountMapper，继承Mapper类，实现map方法。

2.创建一个Java类WordCountReducer，继承Reducer类，实现reduce方法。

3.创建一个Java类WordCount，其中包含main方法，用于运行MapReduce程序。

WordCountMapper.java：

import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable> {

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

  public void map(LongWritable key, Text value, Context context)
      throws IOException, InterruptedException {
    String line = value.toString();
    String[] words = line.split(" ");
    for (String w : words) {
      word.set(w);
      context.write(word, one);
    }
  }
}

WordCountReducer.java：

import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable> {

  public void reduce(Text key, Iterable<IntWritable> values, Context context)
      throws IOException, InterruptedException {
    int sum = 0;
    for (IntWritable val : values) {
      sum += val.get();
    }
    context.write(key, new IntWritable(sum));
  }
}

WordCount.java：

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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class WordCount {

  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(WordCountMapper.class);
    job.setCombinerClass(WordCountReducer.class);
    job.setReducerClass(WordCountReducer.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);
  }
}

在这个例子中，Mapper将输入文件中的每一行分割成单词，并将每个单词作为键，将值设置为1。Reducer将相同的单词聚合在一起，并将它们的值相加，最终输出每个单词的总计数。