learning/prompts/code-explanation/java/01_io_kafka.md

Prompt:
What does this code do?

```java
 package kafka;

 import org.apache.beam.runners.dataflow.options.DataflowPipelineOptions;
 import org.apache.beam.sdk.Pipeline;
 import org.apache.beam.sdk.io.kafka.KafkaIO;
 import org.apache.beam.sdk.io.kafka.KafkaRecord;
 import org.apache.beam.sdk.options.Description;
 import org.apache.beam.sdk.options.PipelineOptionsFactory;
 import org.apache.beam.sdk.transforms.DoFn;
 import org.apache.beam.sdk.transforms.ParDo;
 import org.apache.beam.sdk.values.KV;
 import org.apache.kafka.common.serialization.IntegerDeserializer;
 import org.apache.kafka.common.serialization.StringDeserializer;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 public class ReadKafkaTopic {

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

     public interface ReadKafkaTopicOptions extends DataflowPipelineOptions {
         @Description("Kafka Bootstrap Server")
         String getBootstrapServer();

         void setBootstrapServer(String value);

         @Description("Kafka Topic Name")
         String getTopicName();

         void setTopicName(String value);
     }

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

         Pipeline p = Pipeline.create(options);

         p
                 .apply(KafkaIO.<Integer, String>read()
                         .withBootstrapServers(options.getBootstrapServer())
                         .withTopic(options.getTopicName())
                         .withKeyDeserializer(IntegerDeserializer.class)
                         .withValueDeserializer(StringDeserializer.class)
                 )
                 .apply("Log message", ParDo.of(new DoFn<KafkaRecord<Integer, String>, String>() {
                             @ProcessElement
                             public void processElement(ProcessContext c) {
                                 KV<Integer, String> kv = c.element().getKV();
                                 String message = String.format("Message Key: %s, Message Value: %s",
                                         kv.getKey(), kv.getValue());
                                 LOG.info(message);
                                 c.output(message);
                             }
                         })
                 );

         p.run();
     }
 }
```

Response:
This code snippet uses the Apache Beam KafkaIO connector to read messages from a Kafka topic.

The `ReadKafkaTopicOptions` interface specifies the Kafka bootstrap server and topic name. The `@Description` annotation provides a description of each option. When running the pipeline, use the command-line arguments `--bootstrapServer` and `--topicName` to set these parameters.

```java
     public interface ReadKafkaTopicOptions extends DataflowPipelineOptions {
         @Description("Kafka Bootstrap Server")
         String getBootstrapServer();

         void setBootstrapServer(String value);

         @Description("Kafka Topic Name")
         String getTopicName();

         void setTopicName(String value);
     }
```
In the `main` method, the `PipelineOptionsFactory` class creates a `ReadKafkaTopicOptions` object from the command-line arguments. The `Pipeline.create` method creates a new pipeline with the specified options.

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

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

The pipeline reads messages from the specified Kafka topic using `KafkaIO.read()`. This method configures the Kafka source by providing the bootstrap server, topic name, key deserializer, and value deserializer. Then, the pipeline applies a `ParDo` transform to log the Kafka message key and value.

```java
                 .apply(KafkaIO.<Integer, String>read()
                         .withBootstrapServers(options.getBootstrapServer())
                         .withTopic(options.getTopicName())
                         .withKeyDeserializer(IntegerDeserializer.class)
                         .withValueDeserializer(StringDeserializer.class)
                 )
                 .apply("Log message", ParDo.of(new DoFn<KafkaRecord<Integer, String>, String>() {
                             @ProcessElement
                             public void processElement(ProcessContext c) {
                                 KV<Integer, String> kv = c.element().getKV();
                                 String message = String.format("Message Key: %s, Message Value: %s",
                                         kv.getKey(), kv.getValue());
                                 LOG.info(message);
                                 c.output(message);
                             }
                         })
                 );
```

Finally, the `run` method executes the pipeline.

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