learning/tour-of-beam/learning-content/common-transforms/with-keys/java-example/Task.java

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 * 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
/*
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
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// beam-playground:
//   name: With-keys
//   description: WithKeys example.
//   multifile: false
//   context_line: 46
//   categories:
//     - Quickstart
//   complexity: BASIC
//   tags:
//     - hellobeam


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

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.*;
import org.apache.beam.sdk.values.KV;
import org.apache.beam.sdk.values.PCollection;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Task {

    private static final Logger LOG = LoggerFactory.getLogger(Task.class);

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

        // Create input PCollection
        PCollection<String> input =
                pipeline.apply(
                        Create.of("apple", "banana", "cherry", "durian", "guava", "melon"));

        // The [words] filtered with the applyTransform()
        PCollection<KV<String, String>> output = applyTransform(input);

        output.apply("Log", ParDo.of(new LogOutput<KV<String,String>>("PCollection with-keys value")));

        pipeline.run();
    }

    // Thuis method groups the string collection with its first letter
    static PCollection<KV<String, String>> applyTransform(PCollection<String> input) {
        return input
                .apply(WithKeys.<String, String>of(fruit -> fruit.substring(0, 1))
                        .withKeyType(strings()));
    }

    static class LogOutput<T> extends DoFn<T, T> {
        private String prefix;

        LogOutput() {
            this.prefix = "Processing element";
        }

        LogOutput(String prefix) {
            this.prefix = prefix;
        }

        @ProcessElement
        public void processElement(ProcessContext c) throws Exception {
            LOG.info(prefix + ": {}", c.element());
        }
    }
}