com.google.appengine.tools.mapreduce

Class Mapper<I,K,V>

java.lang.Object

com.google.appengine.tools.mapreduce.Worker<C>

com.google.appengine.tools.mapreduce.Mapper<I,K,V>

Type Parameters:

I - type of input received

K - type of intermediate keys produced

V - type of intermediate values produced

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

IdentityMapper, KeyProjectionMapper

public abstract class Mapper<I,K,V>
extends Worker<C>

Map function for MapReduce computations. A map function processes input values one at a time and generates zero or more output key-value pairs for each. It emits the generated pairs to the Reducer through the MapperContext.

This class is really an interface that might be evolving. In order to avoid breaking users when we change the interface, we made it an abstract class.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Mapper()

Method Summary

Methods

Modifier and Type	Method and Description
protected void	emit(K key, V value) Syntactic sugar for emit(KeyValue.of(key, value))
protected void	emit(O value) Syntactic sugar for getContext().emit(value)
abstract void	map(I value) Processes a single input value, emitting output through the context returned by Worker.getContext() or emit(O).

Methods inherited from class com.google.appengine.tools.mapreduce.Worker

allowSliceRetry, beginShard, beginSlice, endShard, endSlice, estimateMemoryRequirement, getContext, setContext

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Mapper

public Mapper()

Method Detail

emit

protected void emit(K key,
        V value)

Syntactic sugar for emit(KeyValue.of(key, value))

map

public abstract void map(I value)

Processes a single input value, emitting output through the context returned by Worker.getContext() or emit(O).

emit

protected void emit(O value)

Syntactic sugar for getContext().emit(value)