com.twitter.heron.streamlet.impl.sources.StreamletSource Maven / Gradle / Ivy
// 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.streamlet.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;
/**
* StreamletSource is the base class for all streamlet sources.
* The only common stuff amongst all of them is the output streams
*/
public abstract class StreamletSource extends BaseRichSpout
implements IStatefulComponent {
private static final long serialVersionUID = 8583965332619565343L;
private static final String OUTPUT_FIELD_NAME = "output";
@Override
public void initState(State state) { }
@Override
public void preSave(String checkpointId) { }
/**
* The sources implementing streamlet functionality have some properties.
* 1. They all output only one stream
* 2. All streamlet 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(OUTPUT_FIELD_NAME));
}
}