结合案例讲解MapReduce重要知识点 ---------- 内存排序找出每一组中的最大值

待处理数据 内容如下

二次排序：
23 321
23 290
23 567
78 650
78 554
78 756
16 18
16 16
16 15
9 8
9 0
9 3

处理后的数据 内容如下

输出数据：
-----------
9 8
-----------
16	18
----------
23	567
-----------
78	756

MapReduce类FindMax

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
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.Reducer.Context;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;


/**
 * 
 * @author lyd
 *
 *
获取每一组中的最大值？？
二次排序：
23 321
23 290
23 567
78 650
78 554
78 756
16 18
16 16
16 15
9 8
9 0
9 3


输出数据：
-----------
9 8
-----------
16	18
----------
23	567
-----------
78	756
 */
public class FindMax extends ToolRunner implements Tool{

	/**
	 * 自定义的myMapper
	 * @author lyd
	 *
	 */
	static class MyMapper extends Mapper{

		@Override
		protected void setup(Context context)throws IOException, InterruptedException {
		}

		@Override
		protected void map(LongWritable key, Text value,Context context)
				throws IOException, InterruptedException {
			String line = value.toString();
			String lines [] = line.split(" ");
			context.write(new IntWritable(Integer.parseInt(lines[0])), new IntWritable(Integer.parseInt(lines[1])));
		}

		@Override
		protected void cleanup(Context context)throws IOException, InterruptedException {
		}
		
	}
	
	/**
	 * 自定义MyReducer
	 * @author lyd
	 *
	 */
	static class MyReducer extends Reducer{

		@Override
		protected void setup(Context context)throws IOException, InterruptedException {
		}
		
		
		@Override
		protected void reduce(IntWritable key, Iterable value,Context context)
				throws IOException, InterruptedException {
			List li = new ArrayList();
			for (IntWritable i : value) {
				li.add(i.get());
			}
			//排序
			Collections.sort(li);
			context.write(new Text(key.get()+""), new Text(li.get(li.size()-1)+""));
		}
		
		@Override
		protected void cleanup(Context context)throws IOException, InterruptedException {
		}
	}
	
	
	@Override
	public void setConf(Configuration conf) {
		conf.set("fs.defaultFS", "hdfs://hadoop01:9000");
	}

	@Override
	public Configuration getConf() {
		return new Configuration();
	}
	
	/**
	 * 驱动方法
	 */
	@Override
	public int run(String[] args) throws Exception {
		//1、获取conf对象
		Configuration conf = getConf();
		//2、创建job
		Job job = Job.getInstance(conf, "model01");
		//3、设置运行job的class
		job.setJarByClass(FindMax.class);
		//4、设置map相关属性
		job.setMapperClass(MyMapper.class);
		job.setMapOutputKeyClass(IntWritable.class);
		job.setMapOutputValueClass(IntWritable.class);
		FileInputFormat.addInputPath(job, new Path(args[0]));
		
		//5、设置reduce相关属性
		job.setReducerClass(MyReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(Text.class);
		//判断输出目录是否存在，若存在则删除
		FileSystem fs = FileSystem.get(conf);
		if(fs.exists(new Path(args[1]))){
			fs.delete(new Path(args[1]), true);
		}
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		
		//6、提交运行job
		int isok = job.waitForCompletion(true) ? 0 : 1;
		return isok;
	}
	
	/**
	 * job的主入口
	 * @param args
	 */
	public static void main(String[] args) {
		try {
			//对输入参数作解析
			String [] argss = new GenericOptionsParser(new Configuration(), args).getRemainingArgs();
			System.exit(ToolRunner.run(new FindMax(), argss));
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}