com.hazelcast.mapreduce

Class LifecycleMapperAdapter<KeyIn,ValueIn,KeyOut,ValueOut>

java.lang.Object

com.hazelcast.mapreduce.LifecycleMapperAdapter<KeyIn,ValueIn,KeyOut,ValueOut>

Type Parameters:

KeyIn - type of key used in the KeyValueSource

ValueIn - type of value used in the KeyValueSource

KeyOut - key type for mapped results

ValueOut - value type for mapped results

All Implemented Interfaces:

LifecycleMapper<KeyIn,ValueIn,KeyOut,ValueOut>, Mapper<KeyIn,ValueIn,KeyOut,ValueOut>, Serializable

@Beta
public abstract class LifecycleMapperAdapter<KeyIn,ValueIn,KeyOut,ValueOut>
extends Object
implements LifecycleMapper<KeyIn,ValueIn,KeyOut,ValueOut>

The abstract LifecycleMapperAdapter superclass is used to ease building mappers for the Job. Most mappers will only implement the map(Object, Object, Context) method to collect and emit needed key-value pairs.
For more complex algorithms there is the possibility to override the initialize(Context) and finalized(Context) methods as well.

A simple mapper could look like the following example:

 public static class MyMapper extends LifecycleMapperAdapter<Integer, Integer, String, Integer>
 {
   public void map( Integer key, Integer value, Context<String, Integer> collector )
   {
     collector.emit( String.valueOf( key ), value );
   }
 }
 

If you want to know more about the implementation of MapReduce algorithms read the Google Whitepaper on MapReduce.

Since:

3.2

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
LifecycleMapperAdapter()

Method Summary

Methods

Modifier and Type	Method and Description
void	finalized(Context<KeyOut,ValueOut> context) This method is called after the Mapper.map(Object, Object, Context) method is executed for every value and can be used to finalize the internal state of the mapper or to emit a special value.
void	initialize(Context<KeyOut,ValueOut> context) This method is called before the Mapper.map(Object, Object, Context) method is executed for every value and can be used to initialize the internal state of the mapper or to emit a special value.
abstract void	map(KeyIn key, ValueIn value, Context<KeyOut,ValueOut> context) The map method is called for every single key-value pair in the bound KeyValueSource instance on this cluster node and partition. Due to its nature of a DataGrid, Hazelcast distributes values all over the cluster and so this method is executed on multiple servers at the same time. If you want to know more about the implementation of MapReduce algorithms read the Google Whitepaper on MapReduce.

Methods inherited from class java.lang.Object

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

Constructor Detail

LifecycleMapperAdapter

public LifecycleMapperAdapter()

Method Detail

initialize

public void initialize(Context<KeyOut,ValueOut> context)

This method is called before the Mapper.map(Object, Object, Context) method is executed for every value and can be used to initialize the internal state of the mapper or to emit a special value.

Specified by:

initialize in interface LifecycleMapper<KeyIn,ValueIn,KeyOut,ValueOut>

Parameters:

context - Context to be used for emitting values

map

public abstract void map(KeyIn key,
       ValueIn value,
       Context<KeyOut,ValueOut> context)

The map method is called for every single key-value pair in the bound KeyValueSource instance on this cluster node and partition.
Due to its nature of a DataGrid, Hazelcast distributes values all over the cluster and so this method is executed on multiple servers at the same time.
If you want to know more about the implementation of MapReduce algorithms read the Google Whitepaper on MapReduce.

Specified by:

map in interface Mapper<KeyIn,ValueIn,KeyOut,ValueOut>

Parameters:

key - key to map

value - value to map

context - Context to be used for emitting values

finalized

public void finalized(Context<KeyOut,ValueOut> context)

This method is called after the Mapper.map(Object, Object, Context) method is executed for every value and can be used to finalize the internal state of the mapper or to emit a special value.

Specified by:

finalized in interface LifecycleMapper<KeyIn,ValueIn,KeyOut,ValueOut>

Parameters:

context - Context to be used for emitting values