Spring Boot自动配置加载Spring Kafka属性失败

Question

Spring引导加载属性失败。下面是我通过yaml文件使用的属性。

 spring:
  kafka:
    bootstrap-servers: localhost:9092
    consumer:
      auto-commit-interval: 100
      enable-auto-commit: true
      group-id: ********************
      auto-offset-reset: earliest
      value-deserializer: org.springframework.kafka.support.serializer.JsonDeserializer
    producer:
      batch-size: 16384
      buffer-memory: 33554432
      retries: 0
      value-serializer: org.springframework.kafka.support.serializer.JsonSerializer
    listener:
      poll-timeout: 20000

我得到的例外是这个

原因：java.lang.IllegalAccessException:Class org.apache.kafka.common.utils.utils无法访问带有“protected”修饰符的类org.springframework.kafka.support.serializer.JsonDeserializer的成员

我认为构造器是受保护的。请提供一种方法来实例化这个。

Answer 1

没错。见：

protected JsonDeserializer() {
        this((Class<T>) null);
    }

    protected JsonDeserializer(ObjectMapper objectMapper) {
        this(null, objectMapper);
    }

    public JsonDeserializer(Class<T> targetType) {
        this(targetType, new ObjectMapper());
        this.objectMapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, false);
        this.objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    }

JsonDeserializer不是为默认构造函数实例化而设计的，因为它需要知道要反序列化的targetType。

您可以将此类扩展到特定类型：

public class FooJsonDeserializer extends JsonDeserializer<Foo> { }

并已将其用作值反序列化器属性的类值。

或者您可以考虑自定义DefaultKafka消费者工厂：

@Bean
public ConsumerFactory<?, ?> kafkaConsumerFactory(KafkaProperties properties) {
    Map<String, Object> consumerProperties = properties.buildConsumerProperties();
    consumerProperties.put(CommonClientConfigs.METRIC_REPORTER_CLASSES_CONFIG,
            MyConsumerMetricsReporter.class);
    DefaultKafkaConsumerFactory<Object, Object> consumerFactory =
          new DefaultKafkaConsumerFactory<>(consumerProperties);
    consumerFactory.setValueDeserializer(new JsonDeserializer<>(Foo.class));
    return consumerFactory;
}