动态创建容器

Doubao 中英对照 Dynamically Creating Containers

有若干技术可用于在运行时创建监听容器。本节探讨其中一些技术。

MessageListener 实现

如果你直接实现自己的监听器，可以简单地使用容器工厂为该监听器创建一个原始容器：

Java

public class MyListener implements MessageListener<String, String> {

    @Override
    public void onMessage(ConsumerRecord<String, String> data) {
        // ...
    }

}

private ConcurrentMessageListenerContainer<String, String> createContainer(
        ConcurrentKafkaListenerContainerFactory<String, String> factory, String topic, String group) {

    ConcurrentMessageListenerContainer<String, String> container = factory.createContainer(topic);
    container.getContainerProperties().setMessageListener(new MyListener());
    container.getContainerProperties().setGroupId(group);
    container.setBeanName(group);
    container.start();
    return container;
}

Kotlin

class MyListener : MessageListener<String, String> {

    override fun onMessage(data: ConsumerRecord<String, String>) {

        // ...
    }

}

private fun createContainer(
    factory: ConcurrentKafkaListenerContainerFactory<String, String>, topic: String, group: String
): ConcurrentMessageListenerContainer<String, String> {
    val container = factory.createContainer(topic)
    container.containerProperties.setMessageListener(MyListener())
    container.containerProperties.setGroupId(group)
    container.beanName = group
    container.start()
    return container
}

原型 Bean

对于标注了 @KafkaListener 的方法，其容器可以通过将 bean 声明为原型（prototype）作用域来动态创建：

Java

public class MyPojo {

    private final String id;

    private final String topic;

    public MyPojo(String id, String topic) {
        this.id = id;
        this.topic = topic;
    }

    public String getId() {
        return this.id;
    }

    public String getTopic() {
        return this.topic;
    }

    @KafkaListener(id = "#{__listener.id}", topics = "#{__listener.topic}")
    public void listen(String in) {
        System.out.println(in);
    }

}

@Bean
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
MyPojo pojo(String id, String topic) {
    return new MyPojo(id, topic);
}

applicationContext.getBean(MyPojo.class, "one", "topic2");
applicationContext.getBean(MyPojo.class, "two", "topic3");

Kotlin

class MyPojo(val id: String, val topic: String) {

    @KafkaListener(id = "#{__listener.id}", topics = ["#{__listener.topic}"])
    fun listen(`in`: String?) {
        println(`in`)
    }

}

@Bean
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
fun pojo(id: String, topic: String): MyPojo {
    return MyPojo(id, topic)
}

applicationContext.getBean(MyPojo::class.java, "one", "topic2")
applicationContext.getBean(MyPojo::class.java, "two", "topic3")

important

监听器必须具有唯一的 ID。从 2.8.9 版本开始，KafkaListenerEndpointRegistry 新增了一个方法 unregisterListenerContainer(String id)，以允许你重复使用某个 id。注销一个容器并不会 stop() 该容器，你必须自行停止它。