/*
* Copyright (c) 2008-2013, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.mapreduce;
import com.hazelcast.spi.annotation.
Beta;
import java.io.
Serializable;
/**
* <p>
* The interface Mapper is used to build mappers for the {@link Job}. Most mappers will only need to
* implement this interface and the {@link #map(Object, Object, Context)} method to collect and emit needed
* key-value pairs.<br>
* For more complex algorithms there is the possibility to implement the {@link LifecycleMapper} interface and
* override the {@link LifecycleMapper#initialize(Context)} and {@link LifecycleMapper#finalized(Context)}
* methods as well.</p>
* <p>
* A simple mapper could look like the following example:
* <pre>
* public class MyMapper extends Mapper<Integer, Integer, String, Integer>
* {
* public void map( Integer key, Integer value, Context<String, Integer> context )
* {
* context.emit( String.valueOf( key ), value );
* }
* }
* </pre>
* </p>
* <p>
* If you want to know more about the implementation of MapReduce algorithms read the {@see <a
* href="http://research.google.com/archive/mapreduce-osdi04.pdf">Google Whitepaper on MapReduce</a>}.
* </p>
*
* @param <KeyIn> The type of key used in the {@link KeyValueSource}
* @param <ValueIn> The type of value used in the {@link KeyValueSource}
* @param <KeyOut> The key type for mapped results
* @param <ValueOut> The value type for mapped results
* @since 3.2
*/
@
Beta
public interface
Mapper<KeyIn, ValueIn, KeyOut, ValueOut>
extends
Serializable {
/**
* The map method is called for every single key-value pair in the bound {@link KeyValueSource} instance
* on this cluster node and partition.<br>
* Due to it's nature of a DataGrid Hazelcast distributes values all over the cluster and so this method
* is executed on multiple servers at the same time.<br>
* If you want to know more about the implementation of MapReduce algorithms read the {@see <a
* href="http://research.google.com/archive/mapreduce-osdi04.pdf">Google Whitepaper on MapReduce</a>}.
*
* @param key key to map
* @param value value to map
* @param context Context to be used for emitting values
*/
void
map(KeyIn
key, ValueIn
value,
Context<KeyOut, ValueOut>
context);
}