Class <? extends T> Deserializer.getRealClass() method to return the actual
class of the objects from a deserializer
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Key: HADOOP-4192
URL: https://issues.apache.org/jira/browse/HADOOP-4192
Project: Hadoop Core
Issue Type: Bug
Components: mapred
Reporter: Pete Wyckoff
A deserializer can return a subtype of the type it is instantiated to return,
in which case, it may be important for the caller to know the actual type of
the objects this deserializer will return.
An example of this would be
{code}
public class RecordIODeserializer implements Deserializer<Record> {
private Class<? extends Record> getMyRecordClass (Configuration conf); //
gets the specific record io class from a configuration variable set by the
mapper
Record deserialize(Record t) throws IOException { return ... } // obviously
t cannot be Record - must be a subclass of Record.
}
{code}
The caller needs to instantiate the right Record subclass in order to call
deserialize or to implement createKey/value from a recordreader. In this case,
only the Deserializer knows the actual type of the records being returned.
One could instead parameterize TRecordIODeserializer, but in that case, how
does one know the actual type of the object being deserialized until runtime,
so one would still end up with <? extends Record> and the caller would still
need to get the class.
I propose adding a getRealClass that returns the actual subclass being used.
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