1.需求：建立一個獨立消費者，消費 first 主題中資料。

2.在IDEA建立包名：com.kafka.consumer

3.新建一個CustomConsumer類

package com.kafka.consumer;

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.common.serialization.StringDeserializer;

import java.time.Duration;
import java.util.ArrayList;
import java.util.Properties;

public class CustomConsumer {
    public static void main(String[] args) {
        //配置
        Properties properties = new Properties();
        //連線Kafka叢集
 

        properties.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,"hadoop102:9092");
        //反序列化
        properties.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,StringDeserializer.class.getName());
        
 
//GroupId
        properties.put(ConsumerConfig.GROUP_ID_CONFIG,"test");
        //建立消費者物件
        KafkaConsumer<String, String> kafkaConsumer = new KafkaConsumer<>(properties);

        //topic陣列
        ArrayList<String> topics = new ArrayList<>();
        topics.add("first");
        //訂閱topic
        kafkaConsumer.subscribe(topics);
        //處理資料
        while (true){
            ConsumerRecords<String, String> consumerRecords = kafkaConsumer.poll(Duration.ofSeconds(1));
            for (ConsumerRecord<String, String> consumerRecord : consumerRecords) {
                System.out.println(consumerRecord);
            }
        }
    }
}

4.在 IDEA 中執行消費者程式。

5.在 Kafka 叢集控制檯，建立 Kafka 生產者，並輸入資料。 

bin/kafka-console-producer.sh --bootstrap-server hadoop102:9092 --topic first

同時IDEA收到訊息

sumerRecord(topic = first, partition = 1, leaderEpoch = 9, offset = 23, CreateTime = 1653112344357, serialized key size = -1, serialized value size = 5, headers = RecordHeaders(headers = [], isReadOnly = false), key = null, value = hello)