在Spring Kafka中配置分区数时，通常不建议在消费者端硬编码，而是在创建 KafkaListenerContainerFactory 阶段进行统一设置。下面的示例展示了如何在Java配置类中通过 ConsumerConfig.PARTITION_COUNT 属性来明确指定分区数量，从而实现对Kafka分区数的灵活控制。

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.common.serialization.StringDeserializer;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.annotation.KafkaListenerConfigurer;
import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
import org.springframework.kafka.config.KafkaListenerEndpointRegistrar;
import org.springframework.kafka.config.MethodKafkaListenerEndpoint;
import org.springframework.kafka.listener.ConcurrentMessageListenerContainer;
import org.springframework.kafka.listener.config.MethodKafkaListenerEndpointRegistry;
import org.springframework.kafka.support.serializer.ErrorHandlingDeserializer;
import org.springframework.kafka.support.serializer.JsonDeserializer;
import ja va.util.HashMap;
import ja va.util.Map;

@Configuration
public class KafkaConfig implements KafkaListenerConfigurer {

    @Value("${kafka.bootstrap-servers}")
    private String bootstrapServers;

    @Bean
    public ConcurrentKafkaListenerContainerFactory kafkaListenerContainerFactory() {
        ConcurrentKafkaListenerContainerFactory factory = new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(consumerFactory());
        factory.setConcurrency(3); // 设置并发消费者数量
        return factory;
    }

    public ConsumerFactory consumerFactory() {
        Map props = new HashMap<>();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapServers);
        props.put(ConsumerConfig.GROUP_ID_CONFIG, "my-group");
        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
        props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, true);
        props.put(ConsumerConfig.AUTO_COMMIT_INTERVAL_MS_CONFIG, "1000");
        props.put(ConsumerConfig.PARTITION_COUNT, 5); // 设置分区数
        return new DefaultKafkaConsumerFactory<>(props);
    }

    @Override
    public void configureKafkaListeners(KafkaListenerEndpointRegistrar registrar) {
        MethodKafkaListenerEndpointRegistry registry = new MethodKafkaListenerEndpointRegistry();
        registrar.setEndpoints(registry.getEndpoints());
    }
}

在上述示例中，我们通过 PARTITION_COUNT 属性将分区数设置为5。需要特别注意的是，配置的分区数最好与Kafka主题实际拥有的分区数量保持一致，这样才能确保消息的均匀分布与消费的正确性。如果不确定当前主题的具体分区数，可以使用Kafka自带的命令行工具（如 kafka-topics.sh）或通过Kafka管理界面进行查询，从而获得准确的分区信息。