On Tuesday 04 October 2011 10:16 PM, Anuja Kulkarni wrote:
Hi,
We have class hierarchy for output value for both mapper as well as
reducer class as parent (abstract class) , child1,child2,…
We have mapper class which is specified with its outputvalue class as
parent class ; the map function will emit either child1 or child2
depending on the logic we used ( and reducer is having its inputvalue
class as parent class).
But we are getting error as "*java.io.IOException: Type mismatch in
value from map: expected **parent classreceived child class”*
So is this possible to specify parent class as output/inputvalue class
in case of mapper as well as in reducer ; since we want to follow some
object-oriented approach. What will be the correct way of achieving this ?
- Anuja
Hi Anuja,
bq. So is this possible to specify parent class as output/inputvalue
class in case of mapper as well as in reducer ;
I **think** it is not possible.
bq. What will be the correct way of achieving this ?
I feel the following approach works (there could be a better way of
doing this)
Create a TupleWritable instance with either child1 or child2 array as an
argument based on your logic at the mapper side and write the same
TupleWritable instance as a value of Mapper output value.
At the reducer side, get the writable type from the TupleWritable and do
instanceof check to determine the appropriate value type.
--
Thanks&Regards,
Bh.V.S.Kamesh.
