    001/*
    002 * Copyright (c) 2007-2016 Concurrent, Inc. All Rights Reserved.
    003 *
    004 * Project and contact information: http://www.cascading.org/
    005 *
    006 * This file is part of the Cascading project.
    007 *
    008 * Licensed under the Apache License, Version 2.0 (the "License");
    009 * you may not use this file except in compliance with the License.
    010 * You may obtain a copy of the License at
    011 *
    012 *     http://www.apache.org/licenses/LICENSE-2.0
    013 *
    014 * Unless required by applicable law or agreed to in writing, software
    015 * distributed under the License is distributed on an "AS IS" BASIS,
    016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    017 * See the License for the specific language governing permissions and
    018 * limitations under the License.
    019 */
    020
    021package cascading.flow.stream.duct;
    022
    023import cascading.flow.stream.graph.StreamGraph;
    024
    025/**
    026 *
    027 */
    028public abstract class Duct<Incoming, Outgoing>
    029  {
    030  protected Duct<Outgoing, ?> next;
    031  protected Integer ordinal;
    032
    033  Duct()
    034    {
    035    }
    036
    037  Duct( Duct<Outgoing, ?> next )
    038    {
    039    this.next = next;
    040    }
    041
    042  public Duct getNext()
    043    {
    044    return next;
    045    }
    046
    047  public void bind( StreamGraph streamGraph )
    048    {
    049    next = getNextFor( streamGraph );
    050    }
    051
    052  protected Duct getNextFor( StreamGraph streamGraph )
    053    {
    054    return streamGraph.createNextFor( this );
    055    }
    056
    057  /** Called immediately after bind */
    058  public void initialize()
    059    {
    060    }
    061
    062  /**
    063   *
    064   */
    065  public void prepare()
    066    {
    067    // never chain prepare calls
    068    }
    069
    070  public final void receiveFirst( Incoming incoming )
    071    {
    072    receive( null, incoming );
    073    }
    074
    075  public void start( Duct previous )
    076    {
    077    next.start( this );
    078    }
    079
    080  public abstract void receive( Duct previous, Incoming incoming );
    081
    082  public void complete( Duct previous )
    083    {
    084    next.complete( this );
    085    }
    086
    087  public void cleanup()
    088    {
    089    // never chain cleanup calls
    090    }
    091
    092  @Override
    093  public String toString()
    094    {
    095    return getClass().getSimpleName();
    096    }
    097  }