hadoop 2.8 简单数字排序
package mapreduce;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Partitioner;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class Sort {
public static class Map extends Mapper<Object, Text, IntWritable, IntWritable>{
private static IntWritable data = new IntWritable();
public void map(Object key,Text value, Context context) throws IOException,InterruptedException{
String line =value.toString();
data.set(Integer.parseInt(line));
context.write(data, new IntWritable(1));
}
}
public static class Reduce extends Reducer<IntWritable ,IntWritable, IntWritable,IntWritable>{
private static IntWritable linenum = new IntWritable(1);
public void reduce(IntWritable key,Iterable<IntWritable> values,Context context) throws IOException,InterruptedException{
for(IntWritable val:values)
{
context.write(linenum, key);
linenum = new IntWritable(linenum.get()+1);
}
}
}
public static class Partition extends Partitioner<IntWritable,IntWritable>{
@Override
public int getPartition(IntWritable key, IntWritable value, int numPartitions){
int maxnumber = 65536;
int minnumber = -3000;
int bound = (maxnumber-minnumber)/numPartitions+1;
int keynumber = key.get();
for(int i=1;i<=numPartitions;i++){
if(keynumber < minnumber){
return 0;
}
if(keynumber>=minnumber && keynumber<minnumber+i*bound){
return i;
}
}
return numPartitions+1;
}
}
public static void main(String[] args) throws Exception{
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "Sort");
job.setJarByClass(Sort.class);
job.setMapperClass(Map.class);
job.setReducerClass(Reduce.class);
job.setPartitionerClass(Partition.class);
job.setOutputKeyClass(IntWritable.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
Hadoop在Reduct之前会自动对所有的元组进行基于Key的排序(数字从小到大哦,字符串按字母顺序), 上面这段代码正是利用了自动排序的这点, reduce里的:
linenum = new IntWritable(linenum.get()+1)
是给重复出现的数字排序的.
此外重载了Partition类, 这是在map之前,分配各个mapper处理数据的,比如0-10000000的数字给一号机来排序,
10000000-20000000的数字给二号机来排序,以此类推, 通过这样实现了Hadoop分而治之的思想。