learning/katas/java/Core Transforms/CoGroupByKey/CoGroupByKey/src/org/apache/beam/learning/katas/coretransforms/cogroupbykey/Task.java

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 *  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
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 *      http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.beam.learning.katas.coretransforms.cogroupbykey;

import static org.apache.beam.sdk.values.TypeDescriptors.kvs;
import static org.apache.beam.sdk.values.TypeDescriptors.strings;

import org.apache.beam.learning.katas.util.Log;
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.DoFn;
import org.apache.beam.sdk.transforms.MapElements;
import org.apache.beam.sdk.transforms.ParDo;
import org.apache.beam.sdk.transforms.join.CoGbkResult;
import org.apache.beam.sdk.transforms.join.CoGroupByKey;
import org.apache.beam.sdk.transforms.join.KeyedPCollectionTuple;
import org.apache.beam.sdk.values.KV;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.TupleTag;

public class Task {

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

    PCollection<String> fruits =
        pipeline.apply("Fruits",
            Create.of("apple", "banana", "cherry")
        );

    PCollection<String> countries =
        pipeline.apply("Countries",
            Create.of("australia", "brazil", "canada")
        );

    PCollection<String> output = applyTransform(fruits, countries);

    output.apply(Log.ofElements());

    pipeline.run();
  }

  static PCollection<String> applyTransform(
      PCollection<String> fruits, PCollection<String> countries) {

    TupleTag<String> fruitsTag = new TupleTag<>();
    TupleTag<String> countriesTag = new TupleTag<>();

    MapElements<String, KV<String, String>> mapToAlphabetKv =
        MapElements.into(kvs(strings(), strings()))
            .via(word -> KV.of(word.substring(0, 1), word));

    PCollection<KV<String, String>> fruitsPColl = fruits.apply("Fruit to KV", mapToAlphabetKv);
    PCollection<KV<String, String>> countriesPColl = countries
        .apply("Country to KV", mapToAlphabetKv);

    return KeyedPCollectionTuple
        .of(fruitsTag, fruitsPColl)
        .and(countriesTag, countriesPColl)

        .apply(CoGroupByKey.create())

        .apply(ParDo.of(new DoFn<KV<String, CoGbkResult>, String>() {

          @ProcessElement
          public void processElement(
              @Element KV<String, CoGbkResult> element, OutputReceiver<String> out) {

            String alphabet = element.getKey();
            CoGbkResult coGbkResult = element.getValue();

            String fruit = coGbkResult.getOnly(fruitsTag);
            String country = coGbkResult.getOnly(countriesTag);

            out.output(new WordsAlphabet(alphabet, fruit, country).toString());
          }

        }));
  }

}