The correct way for creation of KafkaTemplate in spring boot

问题

I try configure apache kafka in spring boot application. I read this documentation and follow the steps:

1) I add this lines to aplication.yaml:

spring:
  kafka:
    bootstrap-servers: kafka_host:9092
    producer:
      key-serializer: org.apache.kafka.common.serialization.StringDeserializer
      value-serializer: org.apache.kafka.common.serialization.ByteArraySerializer

2) I create new Topic:

    @Bean
    public NewTopic responseTopic() {
        return new NewTopic("new-topic", 5, (short) 1);
    }

And now I want use KafkaTemplate:

private final KafkaTemplate<String, byte[]> kafkaTemplate;

public KafkaEventBus(KafkaTemplate<String, byte[]> kafkaTemplate) {
    this.kafkaTemplate = kafkaTemplate;
}

But Intellij IDE highlights:

To fix this I need create bean:

@Bean
public KafkaTemplate<String, byte[]> myMessageKafkaTemplate() {
    return new KafkaTemplate<>(greetingProducerFactory());
}

And pass to constructor propirties greetingProducerFactory():

@Bean
public ProducerFactory<String, byte[]> greetingProducerFactory() {
    Map<String, Object> configProps = new HashMap<>();
    configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "kafka_hist4:9092");
    configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
    configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, ByteArraySerializer.class);
    return new DefaultKafkaProducerFactory<>(configProps);
}

But then what's the point of setting in application.yaml if I need create ProducerFactory manual?

回答1:

I think you can safely ignore IDEA's warning; I have no problems wiring in Boot's template with different generic types...

@SpringBootApplication
public class So55280173Application {

    public static void main(String[] args) {
        SpringApplication.run(So55280173Application.class, args);
    }

    @Bean
    public ApplicationRunner runner(KafkaTemplate<String, String> template, Foo foo) {
        return args -> {
            template.send("so55280173", "foo");
            if (foo.template == template) {
                System.out.println("they are the same");
            }
        };
    }

    @Bean
    public NewTopic topic() {
        return new NewTopic("so55280173", 1, (short) 1);
    }

}

@Component
class Foo {

    final KafkaTemplate<String, String> template;

    @Autowired
    Foo(KafkaTemplate<String, String> template) {
        this.template = template;
    }

}

and

they are the same

回答2:

By default KafkaTemplate<Object, Object> is created by Spring Boot in KafkaAutoConfiguration class. Since Spring considers generic type information during dependency injection the default bean can't be autowired into KafkaTemplate<String, byte[]>.