Hadoop1.x代码求海量数据最大值

/**
* 数据格式文件为：
* 4
* 7
* 5
* 即每个数字占一行
*/
import java.io.IOException;
import java.net.URI;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
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 TopKApp {

static final String INPUT = "hdfs://192.168.56.100:9000/input";
static final String OUT = "hdfs://192.168.56.100:9000/out";

static final Path INPUT_PATH = new Path(INPUT);
static final Path OUT_PATH = new Path(OUT);

public static void main(String[] args) throws Exception{

Configuration conf = new Configuration();
FileSystem fileSystem = FileSystem.get(new URI(OUT),conf);
if(fileSystem.exists(OUT_PATH)){
fileSystem.delete(OUT_PATH, true);
}
/**
* Map Reduce 天龙八步
*/
Job job = new Job(conf,TopKApp.class.getSimpleName());
FileInputFormat.setInputPaths(job, INPUT_PATH);
job.setMapperClass(MyMapper.class);
job.setReducerClass(MyReducer.class);
job.setOutputKeyClass(LongWritable.class);
job.setOutputValueClass(NullWritable.class);
FileOutputFormat.setOutputPath(job, OUT_PATH);
job.waitForCompletion(true);
}

static class MyMapper extends Mapper<LongWritable,Text,LongWritable,NullWritable>{
@Override
protected void map(
LongWritable key,
Text value,
Mapper<LongWritable, Text, LongWritable, NullWritable>.Context context)
throws IOException, InterruptedException {
context.write(new LongWritable(Long.parseLong(value.toString())), NullWritable.get());
}

}

static class MyReducer extends Reducer<LongWritable,NullWritable,LongWritable,NullWritable>{
long max = Long.MIN_VALUE;
@Override
protected void reduce(
LongWritable k2,
Iterable<NullWritable> v2s,
Reducer<LongWritable, NullWritable, LongWritable, NullWritable>.Context context)
throws IOException, InterruptedException {

long num = k2.get();
if(num > max){
max = num;
}
}

@Override
protected void cleanup(
Reducer<LongWritable, NullWritable, LongWritable, NullWritable>.Context context)
throws IOException, InterruptedException {
context.write(new LongWritable(max), NullWritable.get());
}
}