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From Michael Giannakopoulos <miccagi...@gmail.com>
Subject Map Reduce when downloading files...
Date Wed, 25 May 2011 15:51:39 GMT
Hello guys,
I have written an application that downloads metadata from 3 groups of
Flickr and i implement a map/reduce task so as metadata to be processed by 3
different mappers (each corresponds to one group...). My app runs on single
mode, but when i try to run it in a pseudo-distributed mode hadoop keeps
showing me java.lang.NullPointerException. This happens before even the map
task starts. I suspect that something happens when the mapper tries to
create keys, or something with the encoding of the input file for the
mapper. Exception is the following one:
java.lang.NullPointerException
    at metaFlickrPro.PhotosDownload$MapClass.map(PhotosDownload.java:124)
    at metaFlickrPro.PhotosDownload$MapClass.map(PhotosDownload.java:1)
    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:621)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:305)
    at org.apache.hadoop.mapred.Child.main(Child.java:170)

where "metaFlickrPro" is the package of my application and PhotosDownload is
the public class that contains the static classes of mapper and reducer...
Please, if anyone has encountered a similar problem, i would be grateful if
he/she answered. I have attached the log file from the map-reduce process. I
run hadoop 0.20.2 on Ubuntu 10.04...

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