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.input.FileSplit;

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

import org.apache.hadoop.util.GenericOptionsParser;

public  class InvertedIndex {

     public  static  class Map  extends Mapper<Object, Text, Text, Text> {

         private Text keyInfo =  new Text(); // 存储单词和URL组合

         private Text valueInfo =  new Text(); // 存储词频

         private FileSplit split; // 存储Split对象

        // 实现map函数

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

                 throws IOException, InterruptedException {

            // 获得<key,value>对所属的FileSplit对象

            split = (FileSplit) context.getInputSplit();

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

             while (itr.hasMoreTokens()) {

                // key值由单词和URL组成，如"MapReduce：file1.txt"

                 int splitIndex = split.getPath().toString().indexOf("file");

                keyInfo.set(itr.nextToken() + ":"

                    + split.getPath().toString().substring(splitIndex));

                // 词频初始化为1

                valueInfo.set("1");

                context.write(keyInfo, valueInfo);

            }

        }

    }

     public  static  class Combine  extends Reducer<Text, Text, Text, Text> {

         private Text info =  new Text();

        // 实现reduce函数

         public  void reduce(Text key, Iterable<Text> values, Context context)

                 throws IOException, InterruptedException {

            // 统计词频

             int sum = 0;

             for (Text value : values) {

                sum += Integer. parseInt(value.toString());

            }

             int splitIndex = key.toString().indexOf(":");

            // 重新设置value值由URL和词频组成

            info.set(key.toString().substring(splitIndex + 1) + ":" + sum);

            // 重新设置key值为单词

            key.set(key.toString().substring(0, splitIndex));

            context.write(key, info);

        }

    }

     public  static  class Reduce  extends Reducer<Text, Text, Text, Text> {

         private Text result =  new Text();

        // 实现reduce函数

         public  void reduce(Text key, Iterable<Text> values, Context context)

                 throws IOException, InterruptedException {

            // 生成文档列表

            String fileList =  new String();

             for (Text value : values) {

                fileList += value.toString() + ";";

            }

            result.set(fileList);

            context.write(key, result);

        }

    }

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

        Configuration conf =  new Configuration();

        conf.set("mapred.job.tracker", "192.168.1.2:9001");

        String[] ioArgs =  new String[] { "index_in", "index_out" };

        String[] otherArgs =  new GenericOptionsParser(conf, ioArgs)

                .getRemainingArgs();

         if (otherArgs.length != 2) {

            System. err.println("Usage: Inverted Index <in> <out>");

            System. exit(2);

        }

        Job job =  new Job(conf, "Inverted Index");

        job.setJarByClass(InvertedIndex. class);

        // 设置Map、Combine和Reduce处理类

        job.setMapperClass(Map. class);

        job.setCombinerClass(Combine. class);

        job.setReducerClass(Reduce. class);

        // 设置Map输出类型

        job.setMapOutputKeyClass(Text. class);

        job.setMapOutputValueClass(Text. class);

        // 设置Reduce输出类型

        job.setOutputKeyClass(Text. class);

        job.setOutputValueClass(Text. class);

        // 设置输入和输出目录

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

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

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

    }

}