hadoop null pointer exception

Question

import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.awt.image.Raster;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.xml.soap.Text;


import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapred.*;

public class blur {
public static class BlurMapper extends MapReduceBase implements Mapper<Text, BytesWritable, LongWritable, BytesWritable>
{
    OutputCollector<LongWritable, BytesWritable> goutput;

    int IMAGE_HEIGHT = 240;
    int IMAGE_WIDTH = 320;
    public BytesWritable Gmiu;
    public BytesWritable Gsigma;
    public BytesWritable w;
    byte[] bytes = new byte[IMAGE_HEIGHT*IMAGE_WIDTH*3];
    public BytesWritable emit = new BytesWritable(bytes);
    int count = 0;
    int initVar = 125;
    public LongWritable l = new LongWritable(1);

    public void map(Text key, BytesWritable file,OutputCollector<LongWritable, BytesWritable> output, Reporter reporter) throws IOException {
 //Read Current Image from File.
                    goutput = output;
                    //System.out.println("akhil langer");
                   BufferedImage img = ImageIO.read(new ByteArrayInputStream(file.getBytes()));
                 // BufferedImage dest = null;

                   //Apply Blur on Filter Operation - External JAR
                  // BoxBlurFilter BlurOp = new BoxBlurFilter(10,10,2);
                    Raster ras=img.getData();
                    DataBufferByte db= (DataBufferByte)ras.getDataBuffer();
                    byte[] data = db.getData();
                    byte[] byte1 = new byte[IMAGE_HEIGHT*IMAGE_WIDTH];
                    byte[] byte2 = new byte[IMAGE_HEIGHT*IMAGE_WIDTH];
                    for(int i=0;i<IMAGE_HEIGHT*IMAGE_WIDTH;i++)
                    {
                    byte1[i]=20;
                    byte2[i]=125;
                    }
                    byte [] oldmiu;
                     oldmiu = new byte[IMAGE_HEIGHT*IMAGE_WIDTH] ;
                    byte [] oldsigma;
                     oldsigma = new byte[IMAGE_HEIGHT*IMAGE_WIDTH] ;
                    if(count==0){
                            Gmiu = new BytesWritable(data);
                            Gsigma = new BytesWritable(byte1);
                            w = new BytesWritable(byte2);
                            count++;

                    oldmiu= Gmiu.getBytes();


                    oldsigma= Gmiu.getBytes();
                    }

                        else{
                             for(int i=0;i<IMAGE_HEIGHT*IMAGE_WIDTH;i++)
                             {
                                byte pixel = data[i];
                                Double  tempmiu=new Double(0.0);
                                Double  tempsig=new Double(0.0);
                                Double weight = new Double(0.0);
                                 double temp1=0; double alpha = 0.05;
                                 tempmiu = (1-alpha)*oldmiu[i] + alpha*pixel;
                                 temp1=temp1+(pixel-oldmiu[i])*(pixel-oldmiu[i]);
                                 tempsig=(1-alpha)*oldsigma[i]+ alpha*temp1;

                                 byte1[i] = tempmiu.byteValue();
                                 byte2[i]= tempsig.byteValue();
                                 Gmiu.set(byte1,i,1);
                                 Gsigma.set(byte2,i,1);
                                 byte1 = w.getBytes();
                                 Double w1=new Double((1-alpha)*byte1[i]+alpha*100);
                                 byte2[i] = w1.byteValue();
                                 w.set(byte2,i,1);
                             }

                        }
                        byte1 = Gsigma.getBytes();                       
                        emit.set(byte1,0,IMAGE_HEIGHT*IMAGE_WIDTH);
                        byte1 = Gsigma.getBytes();
                        emit.set(byte1,IMAGE_HEIGHT*IMAGE_WIDTH,IMAGE_HEIGHT*IMAGE_WIDTH);
                        byte1 = w.getBytes();
                        emit.set(byte1,2*IMAGE_HEIGHT*IMAGE_WIDTH,IMAGE_HEIGHT*IMAGE_WIDTH);  
        }

        @Override
         public void close(){
            try{
                goutput.collect(l, emit);
            }
            catch(Exception e){
                e.printStackTrace();
                System.exit(-1);
            }

         }

 }

        public static void main(String[] args) {

                if(args.length!=2) {

                        System.err.println("Usage: blurvideo input  output");
                        System.exit(-1);

                 }
                 JobClient client = new JobClient();
                 JobConf conf = new JobConf(blur.class);


                conf.setOutputValueClass(BytesWritable.class);
                conf.setInputFormat(SequenceFileInputFormat.class);
                //conf.setNumMapTasks(n)

               SequenceFileInputFormat.addInputPath(conf, new Path(args[0]));
                 SequenceFileOutputFormat.setOutputPath(conf, new  Path(args[1]));
              conf.setMapperClass(BlurMapper.class);
              conf.setNumReduceTasks(0);
              //conf.setReducerClass(org.apache.hadoop.mapred.lib.IdentityReducer.class);

                client.setConf(conf);
                try {
                       JobClient.runJob(conf);
                } catch (Exception e) {
                        e.printStackTrace();
                }
        }
}

Error:

java.lang.NullPointerException at blur$BlurMapper.close(blur.java:99) at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:57) at org.apache.hadoop.mapred.MapTask.run(MapTask.java:342) at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:138)

Please reply!

Answer 1

Damn ... my resistance has crumbled.

Evidently, goutput.collect(l, emit); is throwing an NPE. And that means that goutput is null when close() is called.

That means either map was never called, or it was called with an output argument that was null.

I don't know Hadoop, but I suspect that the root problem is your map method is not overriding the map method in the base class because the signature is different. Net result is that your map method is not getting called, and .... NPE.