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  • Volodymyr Bychkovyak thinks this is interesting:

In this case, you need to implement the close() method so that you know when the last record has been read, so you can finish processing the last group of lines.

From

Cover of Hadoop: The Definitive Guide, 3rd Edition

Note

There's no close method in org.apache.hadoop.mapreduce.Mapper. However you can override cleanup method for that purpose.