MapReduce最大值

package com.bw.hadoop;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
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;

public class Max {  
    
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {  
 
        Configuration config = new Configuration();
        config.set("fs.defaultFS", "hdfs://192.168.0.117:9000");
        config.set("yarn.resourcemanager.hostname", "192.168.0.117");
        
        Job job = Job.getInstance(config);
        
        //MR
        job.setMapperClass(MaxMapper.class);
        job.setReducerClass(MaxReducer.class);
        
        //M-O
        job.setMapOutputKeyClass(LongWritable.class);
        job.setMapOutputValueClass(NullWritable.class);
        
        //R-O
        job.setOutputKeyClass(LongWritable.class);
        job.setOutputValueClass(NullWritable.class);
        
        //I-O
        FileInputFormat.setInputPaths(job, new Path("/b"));
        FileOutputFormat.setOutputPath(job, new Path("/Out"));
        
        //boolean
        boolean B = job.waitForCompletion(true);
        if(B){
            System.out.println("Success");
        }else{
            System.out.println("Error");
        }
    }  
 
    public static class MaxMapper extends Mapper<LongWritable, Text, LongWritable, NullWritable> {  
        
        // 定义一个Long类型的最小值作为临时变量  
        private Long max = Long.MIN_VALUE;  
        
        // 定义输出去的value  
        private LongWritable maxValue = new LongWritable();  
 
        @Override  
        protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, LongWritable, NullWritable>.Context context) throws IOException,  
                InterruptedException {  
            
            // 获取输入的行  
            String line = value.toString();  
            
            // 抛弃无效记录  
            if (line == null || line.equals("")) {  
                return;  
            }  
            
            // 把line转换为数值  
            long temp = Long.parseLong(line);  
 
            // 比较大小  
            if (temp > max) {  
                // 把val赋值给tempMax  
                max = temp;  
            }  
 
        }  
 
        /**  
         * cleanUp()是指map函数执行完成之后就会调用，刚好满足我们的要求 因为map()函数执行完成之后我们单个任务的的最大值也就产生了  
         */  
       
        @Override  
        protected void cleanup(Mapper<LongWritable, Text, LongWritable, NullWritable>.Context context) throws IOException, InterruptedException {  
            // 把最后的处理结果写出去  
            maxValue.set(max);  
            context.write(maxValue, NullWritable.get());  
        }  
        
    }  
 
   
    /**
     * 汇总多个任务产生的最大值，再次比较
     */  
    public static class MaxReducer extends Reducer<LongWritable, NullWritable, LongWritable, NullWritable> {  
       
        // 定义一个参考的临时变量  
        private Long max = Long.MIN_VALUE;  
        
        // 定义输出的key  
        private LongWritable maxValue = new LongWritable();  
 
        protected void reduce(LongWritable key, Iterable<NullWritable> value, Reducer<LongWritable, NullWritable, LongWritable, NullWritable>.Context context)  
                throws IOException, InterruptedException {  
            
            if (key.get() > max) {  
                max = key.get();  
            }  
 
        }  
 
       
        /**
         * reduce任务完成后写出去
         */  
        protected void cleanup(Reducer<LongWritable, NullWritable, LongWritable, NullWritable>.Context context) throws IOException, InterruptedException {  
            
            // 设置最大值  
            maxValue.set(max);
            
            context.write(maxValue, NullWritable.get());  
        }  
    }  
}