Kotlin 警告：访问构造函数中的非最终属性

Question

我有一些以下代码并收到变量警告，producer该警告是accessing non-final property in constructor

class KafkaService {

  val producer: KafkaProducer<String, String>

  init {
    val props = Properties()
    props[ProducerConfig.BOOTSTRAP_SERVERS_CONFIG] = "127.0.0.1:9092"
    props[ProducerConfig.CLIENT_ID_CONFIG] = "DemoProducer"
    props[ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG] = StringSerializer::class.java.name
    props[ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG] = StringSerializer::class.java.name

    producer = KafkaProducer(props)
  }

  fun sendToKafka(topic: String, message: String) {
    val producerRecord: ProducerRecord<String?, String> = ProducerRecord(topic, null, message)
    producer.send(producerRecord)
  }
}

解决这个问题的最佳方法是什么？

Answer 1

您应该将producer变量初始化为惰性变量：

class KafkaService {

  val producer: KafkaProducer<String, String> by lazy {
    val props = Properties()
    props[ProducerConfig.BOOTSTRAP_SERVERS_CONFIG] = "127.0.0.1:9092"
    props[ProducerConfig.CLIENT_ID_CONFIG] = "DemoProducer"
    props[ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG] = StringSerializer::class.java.name
    props[ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG] = StringSerializer::class.java.name

    KafkaProducer(props)
  }

  fun sendToKafka(topic: String, message: String) {
    val producerRecord: ProducerRecord<String?, String> = ProducerRecord(topic, null, message)
    producer.send(producerRecord)
  }
}

这样，您的变量将在您第一次访问它时被初始化，并且您不会重新分配最终变量。请阅读本文以更好地理解。