content: /*
   * 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
   * limitations under the License.
   */
  package org.apache.beam.examples;
  
  import java.util.Map;
  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.ParDo;
  import org.apache.beam.sdk.transforms.View;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.PCollectionView;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  // beam-playground:
  //   name: View
  //   description: Demonstration of View transform usage.
  //   multifile: false
  //   default_example: false
  //   context_line: 49
  //   categories:
  //     - Core Transforms
  //   complexity: MEDIUM
  //   tags:
  //     - transforms
  //     - views
  //     - pairs
  
  public class ViewExample {
    public static void main(String[] args) {
      PipelineOptions options = PipelineOptionsFactory.fromArgs(args).create();
      Pipeline pipeline = Pipeline.create(options);
  
      // [START main_section]
      // List of elements
      PCollection<KV<String, String>> citiesToCountries =
          pipeline.apply(
              "Cities and Countries",
              Create.of(
                  KV.of("Beijing", "China"),
                  KV.of("London", "United Kingdom"),
                  KV.of("San Francisco", "United States"),
                  KV.of("Singapore", "Singapore"),
                  KV.of("Sydney", "Australia")));
  
      PCollectionView<Map<String, String>> citiesToCountriesView =
          citiesToCountries.apply(View.asMap());
  
      PCollection<KV<String, String>> persons =
          pipeline.apply(
              "Persons",
              Create.of(
                  KV.of("Henry", "Singapore"),
                  KV.of("Jane", "San Francisco"),
                  KV.of("Lee", "Beijing"),
                  KV.of("John", "Sydney"),
                  KV.of("Alfred", "London")));
  
      PCollection<KV<String, String>> output =
          persons.apply(
              ParDo.of(
                      new DoFn<KV<String, String>, KV<String, String>>() {
                        // Get city from person and get from city view
                        @ProcessElement
                        public void processElement(
                            @Element KV<String, String> person,
                            OutputReceiver<KV<String, String>> out,
                            ProcessContext context) {
                          Map<String, String> citiesToCountries =
                              context.sideInput(citiesToCountriesView);
                          String city = person.getValue();
                          String country = citiesToCountries.get(city);
                          if (country == null) {
                            country = "Unknown";
                          }
                          out.output(KV.of(person.getKey(), country));
                        }
                      })
                  .withSideInputs(citiesToCountriesView));
      // [END main_section]
  
      output.apply("Log", ParDo.of(new LogOutput<>("Output: ")));
  
      pipeline.run();
    }
  
    static class LogOutput<T> extends DoFn<T, T> {
      private static final Logger LOG = LoggerFactory.getLogger(LogOutput.class);
      private final String prefix;
  
      public LogOutput(String prefix) {
        this.prefix = prefix;
      }
  
      @ProcessElement
      public void processElement(ProcessContext c) throws Exception {
        LOG.info(prefix + c.element());
        c.output(c.element());
      }
    }
  }
  