Prompt: Write a sample Java code snippet that writes data in CSV format using Apache Beam.

Response: Your Apache Beam pipeline can write data to CSV files using the CsvIO connector. Here is an example of how to achieve this:

import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.io.csv.CsvIO;
import org.apache.beam.sdk.options.Description;
import org.apache.beam.sdk.options.PipelineOptions;
import org.apache.beam.sdk.options.PipelineOptionsFactory;
import org.apache.beam.sdk.schemas.JavaFieldSchema;
import org.apache.beam.sdk.schemas.annotations.DefaultSchema;
import org.apache.beam.sdk.transforms.Create;
import org.apache.beam.sdk.values.PCollection;
import org.apache.commons.csv.CSVFormat;

import java.io.Serializable;
import java.util.Arrays;
import java.util.List;

public class WriteCsvFile {

    // ExampleRecord is a POJO that represents the data to be written to the CSV file
    @DefaultSchema(JavaFieldSchema.class)
    public static class ExampleRecord implements Serializable {
        public int id;
        public String month;
        public String amount;

        public ExampleRecord() {
        }

        public ExampleRecord(int id, String month, String amount) {
            this.id = id;
            this.month = month;
            this.amount = amount;
        }
    }

    public interface WriteCsvFileOptions extends PipelineOptions {

        @Description("A file path to write CSV files to")
        @Validation.Required
        String getFilePath();

        void setFilePath(String filePath);
    }

    public static void main(String[] args) {
        WriteCsvFileOptions options =
                PipelineOptionsFactory.fromArgs(args)
                        .withValidation().as(WriteCsvFileOptions.class);

        Pipeline p = Pipeline.create(options);

        List<ExampleRecord> rows =
            Arrays.asList(
                new ExampleRecord(1, "January", "$1000"),
                new ExampleRecord(2, "February", "$2000"),
                new ExampleRecord(3, "March", "$3000"));

        CSVFormat csvFormat =
            CSVFormat.DEFAULT.withHeaderComments("CSV file created by Apache Beam")
                .withCommentMarker('#');

        p.apply("Create collection", Create.of(rows))
            .apply(
                "Write to CSV file",
                    CsvIO.<ExampleRecord>write()
                        .to(options.getFilePath())
                        .withNumShards(1));
        p.run();
    }
}