mapreduce 默认排序算法

public class sortapp {
private static final String INPUT_PATH="hdfs://localhost:9000/input";
private static final String OUT_PATH="hdfs://loalhost:9000/output";
public static void main(String args[]) throws Exception{
Configuration conf=new Configuration();
final FileSystem filesystem=FileSystem.get(new URI(INPUT_PATH),conf);
final Path outpath=new Path(OUT_PATH);
if(filesystem.exists(outpath)){
filesystem.delete(outpath,true);
}
final Job job=new Job(conf,sortapp.class.getSimpleName());
//制定输入文件路径
FileInputFormat.setInputPaths(job, INPUT_PATH);
job.setInputFormatClass(TextInputFormat.class);
//1.2指定自定义的Mapper类
job.setMapperClass(MyMapper.class);
job.setMapOutputKeyClass(NewK2.class);//指定输出<k2,v2>的类型
job.setMapOutputValueClass(LongWritable.class);

//1.3 指定分区类
job.setPartitionerClass(HashPartitioner.class);
job.setNumReduceTasks(1);

//2.2 指定自定义的reduce类
job.setReducerClass(MyReducer.class);
job.setOutputKeyClass(LongWritable.class);//指定输出<k3,v3>的类型
job.setOutputValueClass(LongWritable.class);

//2.3 指定输出到哪里
FileOutputFormat.setOutputPath(job, new Path(OUT_PATH));
job.setOutputFormatClass(TextOutputFormat.class);//设定输出文件的格式化类
job.waitForCompletion(true);//把代码提交给JobTracker执行
}

static class MyMapper extends Mapper<LongWritable, Text, NewK2, LongWritable>{
protected void map(LongWritable key, Text value, org.apache.hadoop.mapreduce.Mapper<LongWritable,Text,NewK2,LongWritable>.Context context) throws java.io.IOException ,InterruptedException {
final String[] splited = value.toString().split("\t");
final NewK2 k2 = new NewK2(Long.parseLong(splited[0]), Long.parseLong(splited[1]));
final LongWritable v2 = new LongWritable(Long.parseLong(splited[1]));
context.write(k2, v2);
};
}

static class MyReducer extends Reducer<NewK2, LongWritable, LongWritable, LongWritable>{
protected void reduce(NewK2 k2, java.lang.Iterable<LongWritable> v2s, org.apache.hadoop.mapreduce.Reducer<NewK2,LongWritable,LongWritable,LongWritable>.Context context) throws java.io.IOException ,InterruptedException {
context.write(new LongWritable(k2.first), new LongWritable(k2.second));
};
}

/**
* 问：为什么实现该类？
* 答：因为原来的v2不能参与排序，把原来的k2和v2封装到一个类中，作为新的k2
*
*/
static class  NewK2 implements WritableComparable<NewK2>{
Long first;
Long second;

public NewK2(){}

public NewK2(long first, long second){
this.first = first;
this.second = second;
}

@Override
public void readFields(DataInput in) throws IOException {
this.first = in.readLong();
this.second = in.readLong();
}

@Override
public void write(DataOutput out) throws IOException {
out.writeLong(first);
out.writeLong(second);
}

/**
* 当k2进行排序时，会调用该方法.
* 当第一列不同时，升序；当第一列相同时，第二列升序
*/
@Override
public int compareTo(NewK2 o) {
final long minus = this.first - o.first;
if(minus !=0){
return (int)minus;
}
return (int)(this.second - o.second);
}

@Override
public int hashCode() {
return this.first.hashCode()+this.second.hashCode();
}

@Override
public boolean equals(Object obj) {
if(!(obj instanceof NewK2)){
return false;
}
NewK2 oK2 = (NewK2)obj;
return (this.first==oK2.first)&&(this.second==oK2.second);
}
}

}

}

}