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.tap;
022
023import java.io.IOException;
024
025import cascading.flow.FlowProcess;
026import cascading.scheme.Scheme;
027import cascading.tuple.Fields;
028import cascading.tuple.TupleEntryCollector;
029
030/**
031 * Class SourceTap is an optional base class for source only Taps.
032 * <p/>
033 * Some {@link Tap} instances may only be sources (as opposed
034 * to being a sink). These types should subclass SourceTap for convenience or
035 * set {@link #isSink()} to {@code false} in a custom Tap sub-class.
036 */
037public abstract class SourceTap<Config, Input> extends Tap<Config, Input, Void>
038  {
039  protected SourceTap()
040    {
041    }
042
043  protected SourceTap( Scheme<Config, Input, ?, ?, ?> scheme )
044    {
045    super( (Scheme<Config, Input, Void, ?, ?>) scheme );
046    }
047
048  @Override
049  public Fields getSinkFields()
050    {
051    throw new UnsupportedOperationException( "unable to sink tuple streams via a SourceTap instance" );
052    }
053
054  @Override
055  public final boolean isSink()
056    {
057    return false;
058    }
059
060  @Override
061  public boolean deleteResource( Config conf ) throws IOException
062    {
063    throw new UnsupportedOperationException( "unable to delete files via a SourceTap instance" );
064    }
065
066  @Override
067  public void sinkConfInit( FlowProcess<? extends Config> flowProcess, Config conf )
068    {
069    throw new UnsupportedOperationException( "unable to source tuple streams via a SourceTap instance" );
070    }
071
072  @Override
073  public boolean prepareResourceForWrite( Config conf ) throws IOException
074    {
075    throw new UnsupportedOperationException( "unable to prepare resource for write via a SourceTap instance" );
076    }
077
078  @Override
079  public boolean createResource( Config conf ) throws IOException
080    {
081    throw new UnsupportedOperationException( "unable to make dirs via a SourceTap instance" );
082    }
083
084  @Override
085  public boolean commitResource( Config conf ) throws IOException
086    {
087    throw new UnsupportedOperationException( "unable to commit resource via a SourceTap instance" );
088    }
089
090  @Override
091  public boolean rollbackResource( Config conf ) throws IOException
092    {
093    throw new UnsupportedOperationException( "unable to rollback resource via a SourceTap instance" );
094    }
095
096  @Override
097  public TupleEntryCollector openForWrite( FlowProcess<? extends Config> flowProcess, Void output ) throws IOException
098    {
099    throw new UnsupportedOperationException( "unable to open for write via a SourceTap instance" );
100    }
101  }