Package org.apache.hadoop.mapreduce.lib.aggregate

Class UserDefinedValueAggregatorDescriptor

java.lang.Object

org.apache.hadoop.mapreduce.lib.aggregate.UserDefinedValueAggregatorDescriptor

All Implemented Interfaces:

ValueAggregatorDescriptor

Direct Known Subclasses:

UserDefinedValueAggregatorDescriptor

@Public
@Stable
public class UserDefinedValueAggregatorDescriptor
extends Object
implements ValueAggregatorDescriptor

This class implements a wrapper for a user defined value aggregator descriptor. It serves 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 delegate invocations of generateKeyValPairs function to the created object.

Field Summary

Fields

Modifier and Type	Field	Description
protected ValueAggregatorDescriptor	theAggregatorDescriptor

Fields inherited from interface org.apache.hadoop.mapreduce.lib.aggregate.ValueAggregatorDescriptor

ONE, TYPE_SEPARATOR

Constructor Summary

Constructors

Constructor	Description
UserDefinedValueAggregatorDescriptor(String className, Configuration conf)

Method Summary

Modifier and Type	Method	Description
void	configure(Configuration conf)	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

Field Details

theAggregatorDescriptor

protected ValueAggregatorDescriptor theAggregatorDescriptor

Constructor Details

UserDefinedValueAggregatorDescriptor

public UserDefinedValueAggregatorDescriptor(String className,
 Configuration conf)

Parameters:

className - the class name of the user defined descriptor class

conf - a configure object used for decriptor configuration

Method Details

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(Configuration conf)

Do nothing.

Specified by:

configure in interface ValueAggregatorDescriptor

Parameters:

conf - a Configuration object that may contain the information that can be used to configure the object.