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

java.lang.Object
  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.