learning/prompts/code-explanation/java/07_io_json.md

Prompt:
What does this code do?

```java
package gcs;

import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.io.json.JsonIO;
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.options.Validation;
import org.apache.beam.sdk.schemas.JavaFieldSchema;
import org.apache.beam.sdk.schemas.annotations.DefaultSchema;
import org.apache.beam.sdk.transforms.Create;

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

public class WriteJsonIO {

    @DefaultSchema(JavaFieldSchema.class)
    public static class SampleRecord implements Serializable {
        public int id;
        public String month;
        public String amount

        public SampleRecord() {
        }

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

    public interface WriteJsonOptions extends PipelineOptions {

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

        void setFilePath(String filePath);
    }

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

        Pipeline p = Pipeline.create(options);

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

        p.apply("Create Records", Create.of(rows))
            .apply(
                "Write Records to JSON File",
                    JsonIO.<SampleRecord>write(options.getFilePath())
                        .withNumShards(1));
        p.run();
    }
}
```

Response:
This code snippet uses the Apache Beam JsonIO connector to write a list of `SampleRecord` objects to a JSON file.

The `SampleRecord` class defines the schema for the JSON records and is annotated with `@DefaultSchema(JavaFieldSchema.class)` to indicate that its fields should be used as the schema for the JSON records.

```java
 @DefaultSchema(JavaFieldSchema.class)
    public static class SampleRecord implements Serializable {
        public int id;
        public String month;
        public String amount

        public SampleRecord() {
        }

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

The `WriteJsonOptions` interface specifies command-line options for configuring the output file path. The `@Description` annotation provides a description of the option, and `@Validation.Required` indicates that the option is required.

```java
public interface WriteJsonOptions extends PipelineOptions {

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

        void setFilePath(String filePath);
    }
```

The `PipelineOptionsFactory` class generates `PipelineOptions` from command-line arguments. The `Pipeline.create` method creates a data pipeline, defined as a sequence of transformations to be applied to the data.

```java
  WriteJsonOptions options =
                PipelineOptionsFactory.fromArgs(args)
                        .withValidation().as(WriteJsonOptions.class);

        Pipeline p = Pipeline.create(options);
```

The pipeline generates a list of `SampleRecord` objects and applies the `Create` transform to create a `PCollection` from this list. Subsequently, the `JsonIO.write` transform is used to write the `PCollection` to a JSON file, with the `withNumShards` method specifying the number of output shards.

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

        p.apply("Create Records", Create.of(rows))
            .apply(
                "Write Records to JSON File",
                    JsonIO.<SampleRecord>write(options.getFilePath())
                        .withNumShards(1));
```

Finally, the code snippet invokes the `Pipeline.run` method to execute the pipeline.

```java
        p.run();
```