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

Question

我实现了一个使用Spring Kafka的基本Spring Boot应用程序。我希望我的制作人在第一个<代码>之前连接到Kafka主题。send()被调用，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 方法后连接到 Kafka 主题：

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

智能生命周期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

使用非事务生产者（不提供TransactionIdPrefix），当您第一次调用KafkaTemplate.send时，它会委托给的生产工厂以获取生产者的单个实例。此时，因为以前没有生产者的单个实例，生产者工厂将为您创建这个实例（这就是为什么您看到了日志生产者配置：生产者配置值…）。这个生产者实例现在被所有客户端使用/共享。

因此，如果您想预先创建上面的生产者实例，您可以直接在< code>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;
...

Answer 3

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还为时过早。

相反，添加一个实现智能生命周期的 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;
        }
        
    };
}