java WordCount MapReduce实现源码 最新实现

maven做如下配置

groupId:org.apache.hadoop
artifactId:hadoop-client

version:${hadoop.version}

类申明，继承configured类，并实现Tool接口

public class WordCount extends Configured implements Tool {
}

实现Tool接口的run方法

	public int run(String[] args) throws Exception {
		// TODO Auto-generated method stub
		Job job = Job.getInstance(this.getConf(), this.getClass().getSimpleName());
		job.setJarByClass(this.getClass());	
		FileInputFormat.addInputPath(job, new Path(args[0]));
		
		job.setMapperClass(WordCountMapper.class);
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(IntWritable.class);
		
		job.setReducerClass(WordCountReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		FileOutputFormat.setCompressOutput(job, true);
		FileOutputFormat.setOutputCompressorClass(job, SnappyCodec.class);

		return job.waitForCompletion(true) ? 0: 1;
	}

Mapper类的实现

	public static class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable> {

		@Override
		protected void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {
			String string = value.toString();
			StringTokenizer tokenizer = new StringTokenizer(string);
			
			while (tokenizer.hasMoreTokens()) {
				String text = tokenizer.nextToken();
				context.write(new Text(text), new IntWritable(1));
			}
		}
		
	}

Reducer类的实现

	public static class WordCountReducer 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();
			}
			context.write(key, new IntWritable(sum));
		}
		
	}

最后的Main方法

	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		conf.setBoolean(Job.MAP_OUTPUT_COMPRESS, true);
		conf.setClass(Job.MAP_OUTPUT_COMPRESS_CODEC, SnappyCodec.class, CompressionCodec.class);
		System.exit(ToolRunner.run(conf, new WordCount(), args));
	}