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<div style="text-align: center; color:#151B8D"><big style="font-weight: bold;"><big><big>
Hadoop 進階課程 
</big></big></big></div> <div style="text-align: center; color:#7E2217"><big style="font-weight: bold;"><big>
範例
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[wiki:NCHCCloudCourse100928_4_EXM3 上一關 < ] 第四關 [wiki:NCHCCloudCourse100928_4_EXM5 > 下一關]

 = 說明 =

 * 這關有需要你更正的地方，才可以正確運作喔！

{{{
#!text
WordCount
說明： 
	用於字數統計

測試方法：
	將此程式運作在hadoop 0.20 平台上，執行：
	---------------------------
	hadoop jar WordCount.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>

}}}

 = !WordCount.java =

{{{
#!java
package org.nchc.hadoop;
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.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class WordCount {

	public static class TokenizerMapper extends
			Mapper<Object, Text, Text, IntWritable> {

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

		public void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {
			StringTokenizer itr = new StringTokenizer(value.toString());
			while (itr.hasMoreTokens()) {
				word.set(itr.nextToken());
				context.write(word, one);
			}
		}
	}

	public static class IntSumReducer extends
			Reducer<Text, IntWritable, Text, IntWritable> {
		private IntWritable result = new IntWritable();

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

	public static void main(String[] args) throws Exception {
		// eclipse using
//		String[] argv = { "/user/hadoop/input", "/user/hadoop/output-wc" };
//		args = argv;
		
		Configuration conf = new Configuration();
		
		String[] otherArgs = new GenericOptionsParser(conf, args)
				.getRemainingArgs();
		if (otherArgs.length != 2) {
			System.err
					.println("Usage: hadoop jar WordCount.jar <input> <output>");
			System.exit(2);
		}

		Job job = new Job(conf, "Word Count");
		job.setJarByClass(WordCount.class);
		job.setMapperClass(TokenizerMapper.class);
		job.setCombinerClass(IntSumReducer.class);
		job.setReducerClass(IntSumReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		FileInputFormat.addInputPath(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		CheckAndDelete.checkAndDelete(args[1], conf);
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}

}}}