learning/katas/java/Core Transforms/Flatten/Flatten/src/Task.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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
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import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.options.PipelineOptions;
import org.apache.beam.sdk.options.PipelineOptionsFactory;
import org.apache.beam.sdk.transforms.Create;
import org.apache.beam.sdk.transforms.Flatten;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.PCollectionList;
import util.Log;

class Task {

  public static void main(String[] args) {
    PipelineOptions options = PipelineOptionsFactory.fromArgs(args).create();
    Pipeline pipeline = Pipeline.create(options);

    PCollection<String> wordsStartingWithA =
        pipeline.apply("Words starting with A",
            Create.of("apple", "ant", "arrow")
        );

    PCollection<String> wordsStartingWithB =
        pipeline.apply("Words starting with B",
            Create.of("ball", "book", "bow")
        );

    PCollection<String> output = applyTransform(wordsStartingWithA, wordsStartingWithB);

    output.apply(Log.ofElements());

    pipeline.run();
  }

  static PCollection<String> applyTransform(
      PCollection<String> words1, PCollection<String> words2) {

    return PCollectionList.of(words1).and(words2)
        .apply(Flatten.pCollections());
  }

}