Eclipse+Maven构建Hadoop项目的方法步骤

	4.0.0
 
	practice.hadoop
	simple-examples
	0.0.1-SNAPSHOT
	jar
 
	simple-examples
	http://maven.apache.org
 
	
		UTF-8
	
 
	
		
			junit
			junit
			4.12
			test
		
		
		
			org.apache.hadoop
			hadoop-common
			2.7.0
		
 
		
			org.apache.hadoop
			hadoop-hdfs
			2.7.0
		
		
		
			org.apache.hadoop
			hadoop-client
			2.7.0
		
 		
 		
			org.apache.mrunit
			mrunit
			1.1.0
			hadoop2
			test
		
		
		
			org.apache.hadoop
			hadoop-mapreduce-client-core
			2.7.0
		
		
		
			org.apache.hadoop
			hadoop-yarn-api
			2.7.0
		
		
		
			org.apache.hadoop
			hadoop-auth
			2.7.0
		

		
		
			org.apache.hadoop
			hadoop-minicluster
			2.7.0
			test
		
		
		
			org.apache.hadoop
			hadoop-mapreduce-client-jobclient
			2.7.0
			provided
		
 
	

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 {

		/**
		 * LongWritable, IntWritable, Text 均是 Hadoop 中实现的用于封装 Java
		 * 数据类型的类，这些类实现了WritableComparable接口，
		 * 都能够被串行化从而便于在分布式环境中进行数据交换，你可以将它们分别视为long,int,String 的替代品。
		 */
		private final static IntWritable one = new IntWritable(1); // 值为1
		private Text word = new Text();

		public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
			StringTokenizer itr = new StringTokenizer(value.toString()); // 对字符串进行切分
			while (itr.hasMoreTokens()) {
				word.set(itr.nextToken());
				context.write(word, one); 
			}
		}
	}

	public static class IntSumReducer extends Reducer {
		private IntWritable result = new IntWritable();

		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);
		}
	}

	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
    conf.addResource("classpath:/hadoop/core-site.xml");
    conf.addResource("classpath:/hadoop/hdfs-site.xml");
    conf.addResource("classpath:/hadoop/mapred-site.xml");
//		String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
		String[] otherArgs = {"/input", "/output"};
		if (otherArgs.length != 2) {
			System.err.println("Usage: wordcount  ");
			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.setInputDirRecursive(job, true);
		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}

}