Question

我当前的设置具有以下配置：

@Bean
public ConcurrentKafkaListenerContainerFactory<String, String> myKafkaListenerContainerFactory(
        ConsumerFactory<String, String> consumerFactory) {

    ConcurrentKafkaListenerContainerFactory<String, String> factory = new
            ConcurrentKafkaListenerContainerFactory<>();
    factory.setConsumerFactory(consumerFactory);
    factory.setMessageConverter(stringJsonMessageConverter());

    return factory;
}

stringJsonMessageConverter具有

@Bean
public StringJsonMessageConverter stringJsonMessageConverter() {
    return new StringJsonMessageConverter(objectMapper());
}

利用我的对象映射器

@Bean
public ObjectMapper objectMapper() {
    return new ObjectMapper()
            .registerModule(new JavaTimeModule())
            .registerModule(myCustomJacksonModules())
            .configure(FAIL_ON_UNKNOWN_PROPERTIES, false)
            .configure(ACCEPT_SINGLE_VALUE_AS_ARRAY, true)
            .configure(WRITE_DATES_AS_TIMESTAMPS, false);
}

使用此配置，我可以将其发布为：

...
headers = new MessageHeaders(singletonMap(TOPIC, topic));
Foo foo = ....
Message<?> message = new GenericMessage<>(foo, headers);
kafkaTemplate.send(message);

并消费为：

@KafkaListener(topics = "myTopic",
        groupId = "g1",
        containerFactory = "myKafkaListenerContainerFactory")
public void onMessageReceived(Foo foo) {
    ... works with foo here
}

如果Foo是具体类，则在此示例中可以正常工作。但是，如果Foo是一个摘要，则将其发送为消息是它的子类

F1 extends Foo; F2 extends Foo ...

... // publisher

headers = new MessageHeaders(singletonMap(TOPIC, topic));
F1 f1 = ....
Message<?> message = new GenericMessage<>(f1, headers);
kafkaTemplate.send(message);

... // Listener

@KafkaListener(topics = "myTopic",
        groupId = "g1",
        containerFactory = "myKafkaListenerContainerFactory")
public void onMessageReceived(Foo foo) {
    ... wont work
}

在我的使用者中将Foo声明为类型会失败，但这会起作用：

@KafkaListener(topics = "myTopic",
        groupId = "g1",
        containerFactory = "myKafkaListenerContainerFactory")
public void onMessageReceived(Map<String,Object> fooAsMap) {
    ... this works too
}

除了上面提到的使用Map的选项外，我还尝试了以下方法：

- class level kafka listener ([from here)][1]; it still requires method with param of type Map
- custom deserializer registered in object mapper?

发送消息时是否可以指定目标类型？

Answer 1

在自定义StringJsonMessageConverter所在的DefaultJackson2JavaTypeMapper处配置setTypePrecedence(TypePrecedence.TYPE_ID)。

还要根据发送的类型ID标头设置类型映射以映射到所需的类（仅当生产者的类与消费者的类不同时才需要）。

使用Spring Kafka模板时如何指定类类型？

1 个答案: