在为消费者分配新分区或者移除旧分区时，可以通过消费者API执行一些应用程序代码，在调用subscribe方法时，传进去一个ConsumerRebalanceListener实例就可以了。ConsumerRebalanceListener有两个需要实现的方法。

• onPartitionsRevoked方法会在再均衡开始之前和消费者停止读取消息之后被调用。如果在这里提交偏移量，下一个接管分区的消费者就知道该从哪里开始读取了。要注意，提交的是最近处理过的偏移量，而不是批次中还在处理的最后一个偏移量。因为分区有可能在我们还在处理消息的时候被撤回。我们要提交所有分区的偏移量，而不只是那些即将失去所有权的分区的偏移量——因为提交的偏移量时已经处理过的，所以不会有什么问题。调用commitSync方法，确保在再均衡发生之前提交偏移量。
• onPartitionsAssigned方法会在重新分配分区之后和消费者开始读取消息之前被调用。

package test.kafka.kafkaconsumer

import java.util

import org.apache.kafka.clients.consumer.{ConsumerRebalanceListener, KafkaConsumer, OffsetAndMetadata}
import org.apache.kafka.common.TopicPartition

class HandleRebalance(
                       consumer:KafkaConsumer[String, String],
                       currentOffsets: util.HashMap[TopicPartition, OffsetAndMetadata]
                     ) extends ConsumerRebalanceListener {
  override def onPartitionsRevoked(partitions: util.Collection[TopicPartition]): Unit = {
//    println("Lost partitions in rebalance. Committing current offsets: " + currentOffsets)
    consumer.commitSync(currentOffsets)
  }
  override def onPartitionsAssigned(partitions: util.Collection[TopicPartition]): Unit = {}
}

package test.kafka.kafkaconsumer

import java.util
import java.util.Properties

import org.apache.kafka.clients.consumer._
import org.apache.kafka.common.TopicPartition
import org.apache.kafka.common.errors.WakeupException
import test.kafka.kafkaProperities

object RebalanceListener {
  private val KAFKA_PROPERITIES = new kafkaProperities()

  def main(args: Array[String]): Unit = {
    val kfkConProps: Properties = KAFKA_PROPERITIES.getKakConPros
    val currentOffsets: util.HashMap[TopicPartition, OffsetAndMetadata] = new util.HashMap[TopicPartition, OffsetAndMetadata]()

    val consumer: KafkaConsumer[String, String] = new KafkaConsumer(kfkConProps)

    try {
      consumer.subscribe(util.Arrays.asList(KAFKA_PROPERITIES.TOPIC), new HandleRebalance(consumer, currentOffsets))
      while (true) {
        val consumerRecords: ConsumerRecords[String, String] = consumer.poll(100)
        val records: util.Iterator[ConsumerRecord[String, String]] = consumerRecords.iterator()
        while (records.hasNext){
          val record: ConsumerRecord[String, String] = records.next()
          println("topic: " + record.topic() + " partition: " + record.partition() + " offset: " + record.offset())
          currentOffsets.put(
            new TopicPartition(record.topic(), record.partition()),
            new OffsetAndMetadata(record.offset() + 1, ""))
        }
        consumer.commitAsync(currentOffsets, null)
      }
    } catch {
      case e: WakeupException => println(e)
      case e: Exception => println("Unexpected error:" + e)
    } finally {
      try {
        consumer.commitSync(currentOffsets)
      } finally {
        consumer.close()
      }
    }
  }
}