= Word Index  =

{{{
#!java
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.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;
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;


//	WordIndex
//	說明： 
//		將每個字出於哪個檔案，那一行印出來
//
//	測試方法：
//		將此程式運作在hadoop 0.20 平台上，執行：
//		---------------------------
//		hadoop jar WordIndex.jar <input> <output>
//		---------------------------
//
//	注意：
//1.	在hdfs 上來源檔案的路徑為 你所指定的 <input>
//請注意必須先放資料到此hdfs上的資料夾內，且此資料夾內只能放檔案，不可再放資料夾
//2.	運算完後，程式將執行結果放在hdfs 的輸出路徑為 你所指定的 <output>


public class WordIndex {
	 public static class wordindexM extends
			Mapper<LongWritable, Text, Text, Text> {
		public void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {

			FileSplit fileSplit = (FileSplit) context.getInputSplit();
			
			Text map_key = new Text();
			Text map_value = new Text();
			String line = value.toString();
			StringTokenizer st = new StringTokenizer(line.toLowerCase());
			while (st.hasMoreTokens()) {
				String word = st.nextToken();
				map_key.set(word);
				map_value.set(fileSplit.getPath().getName() + ":" + line);
				context.write(map_key, map_value);
			}
		}
	}


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

		public void reduce(Text key, Iterable<Text> values,
				OutputCollector<Text, Text> output, Reporter reporter)
				throws IOException {
			String v = "";
			StringBuilder ret = new StringBuilder("\n");
			for (Text val : values) {
				v += val.toString().trim();
				if (v.length() > 0)
					ret.append(v + "\n");
			}

			output.collect((Text) key, new Text(ret.toString()));
		}
	}

	public static void main(String[] args) throws IOException,
			InterruptedException, ClassNotFoundException {
		// debug using
//		String[] argv = { "input", "output-wi" };
//		args = argv;

		Configuration conf = new Configuration();
		String[] otherArgs = new GenericOptionsParser(conf, args)
				.getRemainingArgs();
		if (otherArgs.length < 2) {
			System.out.println("hadoop jar WordIndex.jar <inDir> <outDir>");
			return;
		}
		Job job = new Job(conf, "word index");
		job.setJobName("word inverted index");
		job.setJarByClass(WordIndex.class);

		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(Text.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(Text.class);

		job.setMapperClass(wordindexM.class);
		job.setReducerClass(wordindexR.class);
		job.setCombinerClass(wordindexR.class);

		FileInputFormat.setInputPaths(job, args[0]);
		CheckAndDelete.checkAndDelete(args[1], conf);
		FileOutputFormat.setOutputPath(job, new Path(args[1]));

		long start = System.nanoTime();

		job.waitForCompletion(true);

		long time = System.nanoTime() - start;
		System.err.println(time * (1E-9) + " secs.");
	}
}

}}}