001/*
002 * Copyright (c) 2007-2017 Xplenty, 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.scheme;
022
023import java.io.IOException;
024
025import cascading.flow.FlowProcess;
026import cascading.tap.Tap;
027import cascading.tuple.Fields;
028
029/**
030 * Class NullScheme is a {@link Scheme} that neither reads or writes any values.
031 * <p/>
032 * It is typically used as a placeholder where a Scheme instance is needed but generally ignored.
033 */
034public class NullScheme<Config, Input, Output, SourceContext, SinkContext> extends Scheme<Config, Input, Output, SourceContext, SinkContext>
035  {
036  public NullScheme()
037    {
038    }
039
040  public NullScheme( Fields sourceFields, Fields sinkFields )
041    {
042    super( sourceFields, sinkFields );
043    }
044
045  @Override
046  public void sourceConfInit( FlowProcess<? extends Config> flowProcess, Tap<Config, Input, Output> tap, Config conf )
047    {
048    }
049
050  @Override
051  public void sinkConfInit( FlowProcess<? extends Config> flowProcess, Tap<Config, Input, Output> tap, Config conf )
052    {
053    }
054
055  @Override
056  public boolean source( FlowProcess<? extends Config> flowProcess, SourceCall<SourceContext, Input> sourceCall ) throws IOException
057    {
058    return false;
059    }
060
061  @Override
062  public void sink( FlowProcess<? extends Config> flowProcess, SinkCall<SinkContext, Output> sinkCall ) throws IOException
063    {
064
065    }
066
067  @Override
068  public String toString()
069    {
070    return getClass().getSimpleName();
071    }
072  }