Spring Kafka 模板 - 在 Spring Boot 启动时连接到 Kafka 主题

Question

我已经实现了一个使用 Spring Kafka 的基本 Spring Boot 应用程序。我希望我的制作人在调用第一个 .send() 之前连接到 Kafka 主题，但我找不到这样做的方法。这可能吗？

日志显示KafkaTemplate仅在我在16:12:44触发.send方法后才连接到Kafka Topic：

2021-11-24 16:12:12.602  INFO 63930 --- [           main] c.e.k.KafkaProducerExampleApplication    : The following profiles are active: dev
2021-11-24 16:12:13.551  INFO 63930 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2021-11-24 16:12:13.559  INFO 63930 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-11-24 16:12:13.559  INFO 63930 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.53]
2021-11-24 16:12:13.613  INFO 63930 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-11-24 16:12:13.613  INFO 63930 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 974 ms
2021-11-24 16:12:13.989  INFO 63930 --- [           main] pertySourcedRequestMappingHandlerMapping : Mapped URL path [/v2/api-docs] onto method [springfox.documentation.swagger2.web.Swagger2Controller#getDocumentation(String, HttpServletRequest)]
2021-11-24 16:12:14.190  INFO 63930 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2021-11-24 16:12:14.190  INFO 63930 --- [           main] d.s.w.p.DocumentationPluginsBootstrapper : Context refreshed
2021-11-24 16:12:14.207  INFO 63930 --- [           main] d.s.w.p.DocumentationPluginsBootstrapper : Found 1 custom documentation plugin(s)
2021-11-24 16:12:14.239  INFO 63930 --- [           main] s.d.s.w.s.ApiListingReferenceScanner     : Scanning for api listing references
2021-11-24 16:12:14.336  INFO 63930 --- [           main] c.e.k.KafkaProducerExampleApplication    : Started KafkaProducerExampleApplication in 7.055 seconds (JVM running for 7.341)
2021-11-24 16:12:44.550  INFO 63930 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-11-24 16:12:44.550  INFO 63930 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2021-11-24 16:12:44.551  INFO 63930 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 1 ms
2021-11-24 16:12:44.649  INFO 63930 --- [nio-8080-exec-1] o.a.k.clients.producer.ProducerConfig    : ProducerConfig values: 

Answer 1

SmartLifecycle bean 为我们工作，谢谢。

@Component
class KafkaProducer (
    private val userChangeLogTemplate: KafkaTemplate<String, UserChangeLog>
    private val kafkaProperties: MizenKafkaProperties
) : NotificationProducer{

    @Bean
    fun connector(pf: ProducerFactory<String, Any>): SmartLifecycle {
        return object : SmartLifecycle {
            override fun stop() {}
            override fun start() {
                pf.createProducer().close()
            }

            override fun isRunning(): Boolean {
                return false
            }
        }
    }

    override fun sendUserChangeLog(message: UserChangeLog) {
        userChangeLogTemplate.send(kafkaProperties.userChangeLogTopic, message)
    }
}

Answer 2

关于 Linh Vu 的回答，最好不要在 bean 定义中创建连接 - 这在应用程序上下文的生命周期中为时过早。

相反，添加一个实现SmartLifecycle的bean并在start()中创建连接；这样，上下文将在连接之前完全初始化。

@Bean
SmartLifecycle connector(ProducerFactory<Object ,Object> pf) {
    return new SmartLifecycle() {
        
        @Override
        public void stop() {
        }
        
        @Override
        public void start() {
            pf.createProducer().close();
        }
        
        @Override
        public boolean isRunning() {
            return false;
        }
        
    };
}

Answer 3

使用non-transactional producer（未提供transactionIdPrefix），当您第一次调用KafkaTemplate.send 时，它将委托给ProducerFactory 以获取Producer 的单个实例。此时，由于之前没有Producer 的单个实例，ProducerFactory 将为您创建这个（这就是您看到日志ProducerConfig : ProducerConfig values ... 的原因）。这个生产者实例现在被所有客户端使用/共享。

---

所以如果你想预先创建上面的生产者实例，你可以直接在ProducerFactory上调用它，例如：

@Bean
public KafkaTemplate<?, ?> kafkaTemplate(ProducerFactory<Object, Object> kafkaProducerFactory) {
        KafkaTemplate<Object, Object> kafkaTemplate = new KafkaTemplate(kafkaProducerFactory);
        kafkaProducerFactory.createProducer();
        return kafkaTemplate;
...