library/src/main/java/com/datatorrent/lib/stream/RoundRobinHashMap.java

/*
 * Copyright (c) 2013 DataTorrent, 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.datatorrent.lib.stream;

import com.datatorrent.api.DefaultInputPort;
import com.datatorrent.api.DefaultOutputPort;
import com.datatorrent.lib.util.BaseKeyValueOperator;
import java.util.HashMap;

/**
 * <p>
 * An implementation of BaseKeyValueOperator that creates a HashMap tuple from incoming tuples. 
 * <p>
 * If keys[] are set, then each incoming tuple is the value of the key (in-order) till all keys get a value.
 * Once all keys are assigned values, the tuple (HashMap) is emitted, the
 * process of assigning values starts again<br>
 * This is a stateful operator as it waits across window boundary to complete
 * the HashTable<br>
 * <br>
 * <b> StateFull : Yes, </b>Operator maintains index of key across windows. <br>
 * <b> Partitions : Yes </b> <br>
 * <br>
 * <b>Port</b>:<br>
 * <b>data</b>: expects V<br>
 * <b>map</b>: emits HashMap&lt;K,v&gt;<br>
 * <br>
 * <b>Properties</b>:<br>
 * <b>keys[]</b>: Set of keys to insert in the output tuple</b>
 * @displayName Round Robin HashMap
 * @category Stream
 * @tags key value, hashmap
 * @since 0.3.3
 */
public class RoundRobinHashMap<K, V> extends BaseKeyValueOperator<K, V>
{
	/**
	 * Keys for round robin association.
	 */
	protected K[] keys;

	/**
	 * Current key index.
	 */
	protected int cursor = 0;

	private HashMap<K, V> otuple;

	/**
	 * Value input port.
	 */
	public final transient DefaultInputPort<V> data = new DefaultInputPort<V>()
	{
		/**
		 * Emits key, key/val pair, and val based on port connections
		 */
		@Override
		public void process(V tuple)
		{
			if (keys.length == 0) {
				return;
			}
			if (cursor == 0) {
				otuple = new HashMap<K, V>();
			}
			otuple.put(keys[cursor], tuple);
			if (++cursor >= keys.length) {
				map.emit(otuple);
				cursor = 0;
				otuple = null;
			}
		}
	};

	/**
	 * key/value map output port.
	 */
	public final transient DefaultOutputPort<HashMap<K, V>> map = new DefaultOutputPort<HashMap<K, V>>();

	/**
	 * Keys for round robin asspociation, set by application.
	 * 
	 * @param keys
	 */
	public void setKeys(K[] keys)
	{
		this.keys = keys;
	}
}