Getting nullpointerexception while using SequenceFile - java

I am working on a project involving Hadoop and Mahout libraries. I have to use SequenceFile.Writer to write data to a file but I am getting a nullpointer exception when I am trying to use SequenceFile. To better understand my problem I have written a test code which is re-creating the problem and also the error message. I am also adding the code to generate the sample data.
Here first I am generating a sample data based on some distribution in the MyUtil class. Then passing the sample data to do canopy clustering(in the test Class) using Mahout's canopy clustering library. Then trying to write the centriods produced by the canopy clustering algorithm to a file using the SequenceFile.Writer. This is where I am getting the null pointer exception(When Creating the Sequence File Writer)
Thanks in advance for your help.
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
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.Text;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.SequenceFile.Writer;
import org.apache.mahout.clustering.canopy.Canopy;
import org.apache.mahout.clustering.canopy.CanopyClusterer;
import org.apache.mahout.clustering.canopy.CanopyDriver;
import org.apache.mahout.common.distance.EuclideanDistanceMeasure;
import org.apache.mahout.math.Vector;
public class Test {
public static void main(String[] args) throws IOException{
List<Vector> sampleData = new ArrayList<Vector>();
MyUtil.generateSamples(sampleData, 400, 1, 1, 2);
MyUtil.generateSamples(sampleData, 400, 1, 0, .5);
MyUtil.generateSamples(sampleData, 400, 0, 2, .1);
#SuppressWarnings("deprecation")
List<Canopy> canopies = CanopyClusterer.createCanopies(sampleData,
new EuclideanDistanceMeasure(), 3.0, 1.5);
Configuration conf = new Configuration();
File testData = new File("testData/points");
if(!testData.exists()){
testData.mkdir();
}
Path path = new Path("testData/points/file1");
SequenceFile.Writer writer = SequenceFile.createWriter(conf,
SequenceFile.Writer.file(path),
SequenceFile.Writer.keyClass(LongWritable.class),
SequenceFile.Writer.valueClass(Text.class));
for(Canopy canopy: canopies){
System.out.println("Canopy ID: "+canopy.getId()+" centers "+
canopy.getCenter().toString());
writer.append(new LongWritable(canopy.getId()),
new Text(canopy.getCenter().toString()));
}
writer.close();
}
}
MyUtil.generateSamples is just generating the sample data(I have also added the code below). And the error message the above code is throwing is
Exception in thread "main" java.lang.NullPointerException
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1010)
at org.apache.hadoop.util.Shell.runCommand(Shell.java:445)
at org.apache.hadoop.util.Shell.run(Shell.java:418)
at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:650)
at org.apache.hadoop.util.Shell.execCommand(Shell.java:739)
at org.apache.hadoop.util.Shell.execCommand(Shell.java:722)
at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:633)
at org.apache.hadoop.fs.FilterFileSystem.setPermission(FilterFileSystem.java:467)
at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:456)
at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:424)
at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:906)
at org.apache.hadoop.io.SequenceFile$Writer.<init>(SequenceFile.java:1071)
at org.apache.hadoop.io.SequenceFile$RecordCompressWriter.<init>(SequenceFile.java:1371)
at org.apache.hadoop.io.SequenceFile.createWriter(SequenceFile.java:272)
at Test.main(Test.java:39)
To Generate the sample data
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import org.apache.mahout.math.DenseVector;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.random.Normal;
public class MyUtil {
public static void generateSamples(List<Vector> vectors, int num,
double mx, double my, double sd){
Normal xDist = new Normal(mx, sd);
Normal yDist = new Normal(my, sd);
for(int i=0; i<num; i++){
vectors.add(new DenseVector(new double[]{xDist.sample(), yDist.sample()}));
}
}
}
}

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