Hi,
I have a following issue in Hadoop 0.20.2. When i try to use inheritance
with WritableComparables the job is failing. Example If i create a base
writable called as shape
public abstract class ShapeWritable<T> implements WritableComparable<T>
{
}
Then extend this for a concrete class called CircleWritable . Now if my
mapper output is set as ShapeWritable in job configuration and I write a
CircleWriable in collect.write() , the map fails with class mismatch. When
i looked into source code of MapTask.java , i saw the following code
*public** **synchronized** **void* collect(K key, V value,* **int* partition
)* **throws* IOException {
reporter.progress();
* **if* (key.getClass() != keyClass) {
* **throw** **new* IOException("Type mismatch in key from map:
expected "
+ keyClass.getName() + ", recieved "
+ key.getClass().getName());
}
* **if* (value.getClass() != valClass) {
* **throw** **new* IOException("Type mismatch in value from map:
expected "
+ valClass.getName() + ", recieved "
+ value.getClass().getName());
}
Here , we are matching directly classes which means inheritance don't work.
Can anyone tell why its implemented in this way? Is it changed in newer
version of Hadoop?
--
Join me at http://hadoopworkshop.eventbrite.com/
