6. kafka拦截器

• 拦截器定义
  拦截器参数命名为：interceptor.classes。官方文档解析如下：
  

  A list of classes to use as interceptors. Implementing the org.apache.kafka.clients.producer.ProducerInterceptor interface allows you to intercept (and possibly mutate) the records received by the producer before they are published to the Kafka cluster. By default, there are no interceptors.

即拦截发送到kafka服务器之前的消息，且在序列化&反序列化之前调用，序列化&反序列化又在分区策略之前调用，这个调用顺序在[kafka生产者&消费者]已经分析过了。拦截器允许修改key和value，同时拦截器可以指定多个，多个拦截器形成拦截器链，且有先后顺序，假定按照如下方式配置2个拦截器，那么会先调用AProducerInterceptor，再调用BProducerInterceptor，且调用BProducerInterceptor时的ProducerRecord是经过AProducerInterceptor修改过的ProducerRecord（如果在AProducerInterceptor中修改过ProducerRecord的话）：

props.put("interceptor.classes", "com.afei.kafka.interceptor.AProducerInterceptor,com.afei.kafka.interceptor.BProducerInterceptor");

• ProducerInterceptor接口定义源码解读

public