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MapReduce Java API实例-统计单词出现频率

在已实现单次单词频率统计的基础上，本文将详细说明如何处理多个数据集文件（如多个txt文件）的输入问题。

多文件输入的实现方法如下：

多文件输入可以通过Hadoop提供的MultipleInputs类的addInputPath方法来实现。这种方法允许将多个文件路径添加到MapReduce任务中，从而支持批量处理。

以下是完整的代码实现：

package com.badao.multinput;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Mapper;import java.io.IOException;import java.util.StringTokenizer;public class MultInputMapper extends Mapper
   
     {    private Text word = new Text();    private IntWritable one = new IntWritable(1);    @Override    public void map(LongWritable key, Text value, Context context)            throws IOException, InterruptedException {        StringTokenizer stringTokenizer = new StringTokenizer(value.toString());        while (stringTokenizer.hasMoreTokens()) {            word.set(stringTokenizer.nextToken());            context.write(word, one);        }    }}
   

2. Reduce类

package com.badao.multinput;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Reducer;import java.io.IOException;public class MultInputReducer extends Reducer
    
      {    private IntWritable result = new IntWritable();    @Override    public void reduce(Text key, Iterable
     
       values, Context context)            throws IOException, InterruptedException {        int sum = 0;        for (IntWritable val : values) {            sum += val.get();        }        result.set(sum);        context.write(key, result);    }}
     
    

3. Job类

package com.badao.multinput;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.input.MultipleInputs;import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import java.io.IOException;public class MultInputJob {    public static void main(String[] args)            throws InterruptedException, IOException, ClassNotFoundException {        wordCountLocal();    }    public static void wordCountLocal()            throws IOException, ClassNotFoundException, InterruptedException {        Configuration conf = new Configuration();        Job job = Job.getInstance(conf, "multinputwordcount");        job.setJarByClass(MultInputJob.class);        job.setMapperClass(MultInputMapper.class);        job.setCombinerClass(IntSumReducer.class);        job.setReducerClass(MultInputReducer.class);        job.setOutputKeyClass(Text.class);        job.setOutputValueClass(IntWritable.class);        Path path1 = new Path("D:\\words.txt");        Path path2 = new Path("D:\\words2.txt");        MultipleInputs.addInputPath(job, path1, TextInputFormat.class, MultInputMapper.class);        MultipleInputs.addInputPath(job, path2, TextInputFormat.class, MultInputMapper.class);        FileOutputFormat.setOutputPath(job, new Path("D:\\mulinputOut"));        job.waitForCompletion(true);    }}

运行Job类查看效果：

以上实现展示了如何在MapReduce框架中处理多个输入文件。通过MultipleInputs.addInputPath方法，可以轻松地将多个输入路径添加到同一个MapReduce任务中，从而实现多文件批量处理。

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