org.apache.hadoop.mapred.lib.aggregate
Class UserDefinedValueAggregatorDescriptor

java.lang.Object
  extended by org.apache.hadoop.mapred.lib.aggregate.UserDefinedValueAggregatorDescriptor
All Implemented Interfaces:
ValueAggregatorDescriptor

public class UserDefinedValueAggregatorDescriptor
extends Object
implements ValueAggregatorDescriptor

This class implements a wrapper for a user defined value aggregator descriptor. It servs two functions: One is to create an object of ValueAggregatorDescriptor from the name of a user defined class that may be dynamically loaded. The other is to deligate inviokations of generateKeyValPairs function to the created object.


Field Summary
 
Fields inherited from interface org.apache.hadoop.mapred.lib.aggregate.ValueAggregatorDescriptor
ONE, TYPE_SEPARATOR
 
Constructor Summary
UserDefinedValueAggregatorDescriptor(String className, JobConf job)
           
 
Method Summary
 void configure(JobConf job)
          Do nothing.
static Object createInstance(String className)
          Create an instance of the given class
 ArrayList<Map.Entry<Text,Text>> generateKeyValPairs(Object key, Object val)
          Generate a list of aggregation-id/value pairs for the given key/value pairs by delegating the invocation to the real object.
 String toString()
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

UserDefinedValueAggregatorDescriptor

public UserDefinedValueAggregatorDescriptor(String className,
                                            JobConf job)
Parameters:
className - the class name of the user defined descriptor class
job - a configure object used for decriptor configuration
Method Detail

createInstance

public static Object createInstance(String className)
Create an instance of the given class

Parameters:
className - the name of the class
Returns:
a dynamically created instance of the given class

generateKeyValPairs

public ArrayList<Map.Entry<Text,Text>> generateKeyValPairs(Object key,
                                                           Object val)
Generate a list of aggregation-id/value pairs for the given key/value pairs by delegating the invocation to the real object.

Specified by:
generateKeyValPairs in interface ValueAggregatorDescriptor
Parameters:
key - input key
val - input value
Returns:
a list of aggregation id/value pairs. An aggregation id encodes an aggregation type which is used to guide the way to aggregate the value in the reduce/combiner phrase of an Aggregate based job.

toString

public String toString()
Overrides:
toString in class Object
Returns:
the string representation of this object.

configure

public void configure(JobConf job)
Do nothing.

Specified by:
configure in interface ValueAggregatorDescriptor
Parameters:
job - a JobConf object that may contain the information that can be used to configure the object.


Copyright © 2009 The Apache Software Foundation