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Beginner - NullPointerException

Beginner - NullPointerException

New Contributor

Hello everybody,

 

I'm a beginner and i follow a tutorial on cloudera to do my first MapReduce but i have a problem when i run my Jar file :

 

Error: java.lang.NullPointerException
at MonReducer.reduce(MonReducer.java:23)
at MonReducer.reduce(MonReducer.java:1)
at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:171)
at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:627)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:389)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:164)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1917)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)

 

Okay, so my problem is my reducer but i can't find the solution and i don't know how to debug it.

 

My Reducer looks like :

 

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class MonReducer extends Reducer<Text, Text, Text, Text> {
	@Override
	protected void reduce(Text key, Iterable<Text> values,
			Reducer<Text, Text, Text, Text>.Context context)
			throws IOException, InterruptedException {

		final Map<String, Integer> occurences = new HashMap<String, Integer>();

		for (Text value : values) {
			String sValue = value.toString();
			occurences.put(sValue,
					occurences.containsKey(sValue) ? occurences.get(value) + 1 : 1);
		}

		List<String> produits = new ArrayList<String>(occurences.keySet());

		Collections.sort(produits, new Comparator<String>() {

			@Override
			public int compare(String o1, String o2) {
				return occurences.get(o2) - occurences.get(o1);
			}

		});

		String sProduits = "";
		for (String produit : produits) {
			sProduits += produit + ",";
		}

		context.write(key, new Text(sProduits));

	}
}

Did you see any errors ? How can i debug it ?

 

Thank you !!

 

1 REPLY 1

Re: Beginner - NullPointerException

New Contributor

@Ingvald wrote:

Hello everybody,

 

I'm a beginner and i follow a tutorial on cloudera to do my first MapReduce but i have a problem when i run my Jar file :

 

Error: java.lang.NullPointerException
at MonReducer.reduce(MonReducer.java:23)
at MonReducer.reduce(MonReducer.java:1)
at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:171)
at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:627)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:389)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:164)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1917)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)

 

Okay, so my problem is my reducer but i can't find the solution and i don't know how to debug it.

 

 

Did you see any errors ? How can i debug it ?

 

Thank you !!

 


I'm bumping up this question. I hope someone can help.