驱动程序类:
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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
public class DRIVER {
public static void main(String arg[])
{
try{
Path in = new Path("aamazon.txt");
Path out = new Path("/output");
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
job.setJarByClass(DRIVER.class);
job.setMapperClass(MAPPER.class);
job.setReducerClass(REDUCER.class);
job.setNumReduceTasks(0);
FileInputFormat.addInputPath(job, in);
FileOutputFormat.setOutputPath(job, out);
job.waitForCompletion(true);
System.out.println("Successful");}
catch(Exception e){
System.out.println(e.getMessage());
}
}
}
Mapper类:
import java.io.IOException;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
public class MAPPER extends Mapper<LongWritable,Text,LongWritable,Text>{
@Override
public void map(LongWritable key,Text value,Context con)
{
try
{
System.out.println(key +"\n"+ value);
con.write(key, value);
}
catch(Exception e)
{
System.out.println(e.getMessage());
}
}
}
减速机等级:
import java.io.IOException;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
public class REDUCER extends Reducer<LongWritable,Text,LongWritable,Text>{
@Override
public void reduce(LongWritable key,Iterable<Text> value , Context con)
{
System.out.println("reducer");
try{
for(Text t:value)
{
con.write(key, t);
}
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
}
}
问题:
setNumReduceTasks(0)
,那么Mapper就不会被调用任何想法有什么不对?
答案 0 :(得分:0)
您已将减少任务的数量设置为零。
Job job = Job.getInstance(conf);
job.setJarByClass(DRIVER.class);
job.setMapperClass(MAPPER.class);
job.setReducerClass(REDUCER.class);
job.setNumReduceTasks(0); // this should be greater than 0
即便如此,如果它不起作用,请检查您是否拥有&#34; / output&#34;以下行的路径 -
Path out = new Path("/output"); // it is in the root folder. change it to "./output"