天津东软实训第八天------倒排索引

倒排索引流程图：（有三个文件，里边有三句话，分别统计每个单词在每个文件中出现的次数）

package com.young;

import org.apache.commons.lang.StringUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
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.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import java.io.IOException;
public class App 
{
    public static class MyMap extends Mapper<LongWritable,Text,Text,IntWritable>{
        @Override
        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String line = value.toString();//按行读取文件
            String[] fields = StringUtils.split(line," ");//按空格进行分片
            FileSplit fileSplit = (FileSplit) context.getInputSplit();
            String fileName = fileSplit.getPath().getName();//获取文件名
            for(String field:fields)
            {
               context.write(new Text(field+"-->" + fileName),new IntWritable(1));
            }
        }
    }
    public static class MyReduce extends Reducer<Text,IntWritable,Text,IntWritable>{
        @Override
        protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            int sum = 0;
            for(IntWritable value:values)
            {
                sum+=value.get();//统计每个key值对应的value值
            }
            context.write(key,new IntWritable(sum));
        }
    }
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS","hdfs://192.168.131.142:9000");
        Job job  = Job.getInstance(conf);
        job.setJarByClass(App.class);
        job.setMapperClass(MyMap.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        job.setReducerClass(MyReduce.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job,new Path("/idea/a.txt"));//读取HDFS上idea目录下的a.txt文件
        FileInputFormat.addInputPath(job,new Path("/idea/b.txt"));
        FileInputFormat.addInputPath(job,new Path("/idea/c.txt"));
        FileOutputFormat.setOutputPath(job,new Path("/idea/out3"));//将结果保存在idea目录下的out3目录下
        job.waitForCompletion(true);
    }

}