Spring Boot Kafka事务疑问：KafkaTransactionManager未注入及Jpa日志问题

1. KafkaTransactionManager未自动注入 #

我们在自定义配置类KafkaProducerConfiguration中为ProducerFactory配置了ProducerConfig.TRANSACTIONAL_ID_CONFIG = "transaction-"，但KafkaAutoConfiguration中负责创建KafkaTransactionManager的Bean并未自动生成。查看自动配置逻辑：

@Bean
@ConditionalOnProperty(
    name = {"spring.kafka.producer.transaction-id-prefix"}
)
@ConditionalOnMissingBean
public KafkaTransactionManager<?, ?> kafkaTransactionManager(ProducerFactory<?, ?> producerFactory) {
    return new KafkaTransactionManager(producerFactory);
}

可以看到该Bean的创建条件是存在spring.kafka.producer.transaction-id-prefix配置且无自定义KafkaTransactionManagerBean。这说明spring.kafka.producer.transaction-id-prefix与ProducerConfig.TRANSACTIONAL_ID_CONFIG并非同一配置，且我们在ProducerConfig中未找到对应spring.kafka.producer.transaction-id-prefix的常量。

2. 日志中出现JpaTransactionManager #

在带有@Transactional注解的TestService方法中调用kafkaTemplate.send()时，日志显示JpaTransactionManager在处理事务提交，但事务却成功执行。相关代码如下：

@AllArgsConstructor
@Service
public class TestService {
    private final KafkaTemplate<Long, Message> kafkaTemplate;
    
    @Transactional
    public void test(Long id, Message message){
        kafkaTemplate.send("topic", id, message);
    }
}

日志片段：

15:56:14.406 [http-nio-8081-exec-2] DEBUG o.s.orm.jpa.JpaTransactionManager - Initiating transaction commit
15:56:14.406 [http-nio-8081-exec-2] DEBUG o.s.orm.jpa.JpaTransactionManager - Committing JPA transaction on EntityManager [SessionImpl(1789264984<open>)]
15:56:14.511 [http-nio-8081-exec-2] DEBUG o.s.orm.jpa.JpaTransactionManager - Closing JPA EntityManager [SessionImpl(1789264984<open>)] after transaction

疑问 #

• 为何KafkaTransactionManager未被注入，但Kafka事务仍能成功执行？
• 为何日志中会出现JpaTransactionManager而非KafkaTransactionManager？

内容的提问来源于stack exchange，提问作者CostaVi