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在ConsumerConfig这个类中定义了这个属性的默认值，如下图

也就是默认值为latest,它的含义是：如果没有客户端提交过offset的话，当新的客户端消费时，把最新的offset设置为当前消费的offset.

默认是自动提交位移的，每5秒进行一次提交。可以通过参数配置手动提交。

手动提交offset的示例

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.common.PartitionInfo;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.serialization.StringDeserializer;
import org.apache.kafka.common.serialization.StringSerializer;import java.time.Duration;
import java.time.temporal.TemporalUnit;
import java.util.*;
import java.util.concurrent.TimeUnit;
/*
设置手动提交offset*/public class KafkaTest08 {private static Properties getProperties(){Properties properties=new Properties();properties.setProperty(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());properties.setProperty(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());properties.setProperty(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,"xx.xx.xx.xx:9092");properties.setProperty(ConsumerConfig.GROUP_ID_CONFIG,"testGroup8");//设置手动提交位移properties.setProperty(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG,"false");return properties;}public static void main(String[] args) {KafkaConsumer<String,String> myConsumer=new KafkaConsumer<String, String>(getProperties());myConsumer.subscribe(Arrays.asList("student"));int i=0;while(true){ConsumerRecords<String,String> consumerRecords=myConsumer.poll(Duration.ofMillis(5000));for(ConsumerRecord record: consumerRecords){System.out.println(record.value());System.out.println("record offset is: "+record.offset());}myConsumer.commitSync();if(i==0){//myConsumer.commitSync();i ++;}else {i ++;}}}
}