hadoop求最大值方法

hadoop求最大值问题，代码比求最值前N个要简单一些，因为直接使用LongWritable类型，不需要自定义hadoop对象进行比较，所以直接覆盖map和reduce方法，并且覆盖cleanup方法，这是在map和reduce都执行完成之后才会执行的方法，只需要把最大值写入即可

public class MySuper {
	public static void main(String[] args) throws Exception {
		final String INPUT_PATHs = "hdfs://chaoren:9000/seq100w.txt";
		final String OUT_PATHs = "hdfs://chaoren:9000/out";
		Configuration conf = new Configuration();
		final FileSystem fileSystem = FileSystem.get(new URI(INPUT_PATHs), conf);
		final Path outPath = new Path(OUT_PATHs);
		if(fileSystem.exists(outPath)){
			fileSystem.delete(outPath, true);
		}
		
		final Job job = new Job(conf , MySuper.class.getSimpleName());
		FileInputFormat.setInputPaths(job, INPUT_PATHs);
		job.setMapperClass(MyMapper2.class);
		job.setReducerClass(MyReducer2.class);
		job.setOutputKeyClass(LongWritable.class);
		job.setOutputValueClass(NullWritable.class);
		FileOutputFormat.setOutputPath(job, outPath);
		job.waitForCompletion(true);
	}
}

 class MyMapper2 extends Mapper<LongWritable, Text, LongWritable, NullWritable>{
	long max = Long.MIN_VALUE;
	protected void map(LongWritable k1, Text v1, Context context) throws java.io.IOException ,InterruptedException {
		final long temp = Long.parseLong(v1.toString());
		if(temp>max){
			max = temp;
		}
	};
	
	protected void cleanup(org.apache.hadoop.mapreduce.Mapper<LongWritable,Text,LongWritable, NullWritable>.Context context) throws java.io.IOException ,InterruptedException {
		context.write(new LongWritable(max), NullWritable.get());
	};
}

 class MyReducer2 extends Reducer<LongWritable, NullWritable, LongWritable, NullWritable>{
	long max = Long.MIN_VALUE;
	protected void reduce(LongWritable k2, java.lang.Iterable<NullWritable> arg1, org.apache.hadoop.mapreduce.Reducer<LongWritable,NullWritable,LongWritable,NullWritable>.Context arg2) throws java.io.IOException ,InterruptedException {
		final long temp = k2.get();
		if(temp>max){
			max = temp;
		}
	};
	
	protected void cleanup(org.apache.hadoop.mapreduce.Reducer<LongWritable,NullWritable,LongWritable,NullWritable>.Context context) throws java.io.IOException ,InterruptedException {
		context.write(new LongWritable(max), NullWritable.get());
	};
}