com.twitter.heron.dsl.impl.sources.DslSource Maven / Gradle / Ivy

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//  Copyright 2017 Twitter. 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.twitter.heron.dsl.impl.sources;

import java.io.Serializable;

import com.twitter.heron.api.spout.BaseRichSpout;
import com.twitter.heron.api.state.State;
import com.twitter.heron.api.topology.IStatefulComponent;
import com.twitter.heron.api.topology.OutputFieldsDeclarer;
import com.twitter.heron.api.tuple.Fields;

/**
 * DslSource is the base class for all dsl sources.
 * The only common stuff amongst all of them is the output streams
 */
public abstract class DslSource extends BaseRichSpout
    implements IStatefulComponent {

  private static final long serialVersionUID = 8583965332619565343L;
  private static final String OUTPUTFIELDNAME = "output";

  @Override
  public void initState(State state) { }

  @Override
  public void preSave(String checkpointId) { }

  /**
   * The sources implementing dsl functionality have some properties.
   * 1. They all output only one stream
   * 2. All dsl operators should be able to consume their output
   * This imply that the output stream should be named same for all of them.
   */
  @Override
  public void declareOutputFields(OutputFieldsDeclarer outputFieldsDeclarer) {
    outputFieldsDeclarer.declare(new Fields(OUTPUTFIELDNAME));
  }
}