heron/api/src/java/org/apache/heron/streamlet/impl/streamlets/TransformStreamlet.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.heron.streamlet.impl.streamlets;

import java.util.Set;

import org.apache.heron.api.topology.TopologyBuilder;
import org.apache.heron.streamlet.SerializableTransformer;
import org.apache.heron.streamlet.impl.StreamletImpl;
import org.apache.heron.streamlet.impl.operators.TransformOperator;

/**
 * TransformStreamlet represents a Streamlet that is made up of applying the user
 * supplied transform function to each element of the parent streamlet. It differs
 * from the simple MapStreamlet in the sense that it provides setup/cleanup flexibility
 * for the users to setup things and cleanup before the beginning of the computation
 */
public class TransformStreamlet<R, T> extends StreamletImpl<T> {
  private StreamletImpl<R> parent;
  private SerializableTransformer<? super R, ? extends T> serializableTransformer;

  public TransformStreamlet(StreamletImpl<R> parent,
                       SerializableTransformer<? super R, ? extends T> serializableTransformer) {
    this.parent = parent;
    this.serializableTransformer = serializableTransformer;
    setNumPartitions(parent.getNumPartitions());
  }

  @Override
  public boolean doBuild(TopologyBuilder bldr, Set<String> stageNames) {
    setDefaultNameIfNone(StreamletNamePrefix.TRANSFORM, stageNames);
    bldr.setBolt(getName(), new TransformOperator<R, T>(serializableTransformer),
        getNumPartitions()).shuffleGrouping(parent.getName(), parent.getStreamId());
    return true;
  }
}