UserDefinedValueAggregatorDescriptor (Hadoop 1.2.1 API)
Date: 2013-07-22

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## 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.

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