| /* |
| * 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. |
| */ |
| 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.Flatten; |
| import org.apache.beam.sdk.transforms.ParDo; |
| import org.apache.beam.sdk.values.PCollection; |
| import org.apache.beam.sdk.values.PCollectionList; |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| // beam-playground: |
| // name: Flatten |
| // description: Demonstration of Flatten transform usage. |
| // multifile: false |
| // default_example: false |
| // context_line: 46 |
| // categories: |
| // - Core Transforms |
| // complexity: BASIC |
| // tags: |
| // - transforms |
| // - numbers |
| |
| public class FlattenExample { |
| public static void main(String[] args) { |
| PipelineOptions options = PipelineOptionsFactory.create(); |
| Pipeline pipeline = Pipeline.create(options); |
| // [START main_section] |
| // Flatten takes a PCollectionList of PCollection objects of a given type. |
| // Returns a single PCollection that contains all of the elements in the PCollection objects in |
| // that list. |
| PCollection<String> pc1 = pipeline.apply(Create.of("Hello")); |
| PCollection<String> pc2 = pipeline.apply(Create.of("World", "Beam")); |
| PCollection<String> pc3 = pipeline.apply(Create.of("Is", "Fun")); |
| PCollectionList<String> collections = PCollectionList.of(pc1).and(pc2).and(pc3); |
| |
| PCollection<String> merged = collections.apply(Flatten.pCollections()); |
| // [END main_section] |
| // Log values |
| merged.apply(ParDo.of(new LogOutput<>("PCollection numbers after Flatten transform: "))); |
| 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()); |
| } |
| } |
| } |