Apache Kafka和GCP PubSub是两种不同的消息传递系统，它们在设计和使用方式上存在一些区别。

1. 设计和架构:

• Apache Kafka: Kafka是一个分布式的流处理平台，基于发布-订阅模型。它使用持久化日志存储消息，并将消息按照主题分区保存在多个服务器上。Kafka提供了高吞吐量、持久化存储和可水平扩展的特性。
• GCP PubSub: PubSub是Google Cloud Platform提供的一项托管式消息传递服务。它采用了发布-订阅模型，可以将消息在多个订阅者之间传递。PubSub提供了可靠的消息传递、可扩展性和灵活的订阅管理等功能。

2. 代码示例: 下面是使用Apache Kafka和GCP PubSub发送和接收消息的示例代码：

Apache Kafka示例代码：

// 生产者代码
import org.apache.kafka.clients.producer.*;
import java.util.Properties;

public class KafkaProducerExample {
    public static void main(String[] args) {
        Properties props = new Properties();
        props.put("bootstrap.servers", "localhost:9092");
        props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
        props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

        Producer producer = new KafkaProducer<>(props);
        ProducerRecord record = new ProducerRecord<>("my_topic", "key", "value");

        producer.send(record, new Callback() {
            @Override
            public void onCompletion(RecordMetadata metadata, Exception exception) {
                if (exception != null) {
                    exception.printStackTrace();
                } else {
                    System.out.println("Message sent successfully");
                }
            }
        });

        producer.close();
    }
}

// 消费者代码
import org.apache.kafka.clients.consumer.*;
import org.apache.kafka.common.TopicPartition;

import java.util.Collections;
import java.util.Properties;

public class KafkaConsumerExample {
    public static void main(String[] args) {
        Properties props = new Properties();
        props.put("bootstrap.servers", "localhost:9092");
        props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
        props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
        props.put("group.id", "my_group");

        Consumer consumer = new KafkaConsumer<>(props);
        consumer.subscribe(Collections.singletonList("my_topic"));

        while (true) {
            ConsumerRecords records = consumer.poll(1000);
            for (ConsumerRecord record : records) {
                System.out.println("Received message: " + record.value());
            }
        }
    }
}

GCP PubSub示例代码：

// 发布者代码
import com.google.cloud.pubsub.v1.Publisher;
import com.google.pubsub.v1.PubsubMessage;
import com.google.protobuf.ByteString;

public class PubSubPublisherExample {
    public static void main(String[] args) throws Exception {
        String projectId = "your-project-id";
        String topicId = "your-topic-id";

        Publisher publisher = Publisher.newBuilder(topicName).build();

        ByteString data = ByteString.copyFromUtf8("Hello, PubSub!");

        PubsubMessage pubsubMessage = PubsubMessage.newBuilder()
                .setData(data)
                .build();

        publisher.publish(pubsubMessage);

        publisher.shutdown();
    }
}

// 订阅者代码
import com.google.cloud.pubsub.v1.Subscriber;
import com.google.cloud.pubsub.v1.SubscriptionAdminClient;
import com.google.pubsub.v1.SubscriptionName;
import com.google.pubsub.v1.ProjectSubscriptionName;
import com.google.pubsub.v1.PubsubMessage;

public class PubSubSubscriberExample {
    public static void main(String[] args) throws Exception {
        String projectId = "your-project-id";
        String subscriptionId = "your-subscription-id";

        ProjectSubscriptionName subscriptionName = ProjectSubscriptionName.of(projectId, subscriptionId);

        Subscriber subscriber = Subscriber.newBuilder(subscriptionName, new MessageReceiver() {
            @Override
            public void receiveMessage(PubsubMessage message, AckReplyConsumer consumer) {
                System.out.println("Received message: " + message.getData().toStringUtf8());
                consumer.ack();
            }
        }).build();

        subscriber.start();
    }
}

这些示例代码演示了如何在Apache Kafka和GCP PubSub中