contrib/src/main/java/org/apache/apex/malhar/contrib/mqtt/AbstractSinglePortMqttInputOperator.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.apex.malhar.contrib.mqtt;

import org.fusesource.mqtt.client.Message;
import com.datatorrent.api.DefaultOutputPort;

/**
 * This is the base implementation for a single port MQTT input operator. 
 * Subclasses should implement the methods which convert MQTT messages to tuples.
 * <p>
 * Ports:<br>
 * <b>Input</b>: No input port<br>
 * <b>Output</b>: Can have one output port<br>
 * <br>
 * Properties:<br>
 * None<br>
 * <br>
 * Compile time checks:<br>
 * None<br>
 * <br>
 * Run time checks:<br>
 * None<br>
 * <br>
 * <b>Benchmarks</b>:TBD
 * </p>
 * @displayName Abstract Single Port MQTT Input
 * @category Messaging
 * @tags input operator
 * @since 0.9.3
 */
public abstract class AbstractSinglePortMqttInputOperator<T> extends AbstractMqttInputOperator
{
  /**
   * This output port emits tuples, which were extracted from MQTT messages.
   */
  public final transient DefaultOutputPort<T> outputPort = new DefaultOutputPort<T>();

  /**
   * Any concrete class derived from AbstractSinglePortMqttInputOperator has to implement this method
   * so that it knows what type of data it will receive from MQTT
   * It converts a MQTT Message into a Tuple. A Tuple can be of any type (derived from Java Object) that
   * operator user intends to.
   *
   * @param message
   */
  public abstract T getTuple(Message message);

  @Override
  public void emitTuple(Message message)
  {
    T t = getTuple(message);
    if (t != null) {
      outputPort.emit(t);
    }
  }

}