001    /*
002     * Copyright (c) 2007-2015 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    
021    package cascading.tap;
022    
023    import java.io.IOException;
024    
025    import cascading.flow.FlowProcess;
026    import cascading.scheme.Scheme;
027    import cascading.tuple.Fields;
028    import 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     */
037    public 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<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<Config> flowProcess, Void output ) throws IOException
098        {
099        throw new UnsupportedOperationException( "unable to open for write via a SourceTap instance" );
100        }
101      }