Getting Started with Kafka, Consumer Group Case (19)

pom file

    <dependencies>
        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka-clients</artifactId>
            <version>3.0.0</version>
        </dependency>
    </dependencies>

Standalone Consumer Case (Subscription Subject)

In the consumer API code, the consumer id must be configured. Start the consumer from the command line and do not fill in the consumer group id, it will be automatically filled with a random consumer group id

package com.longer.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) {
    
    
        //创建消费者的配置对象
        Properties properties=new Properties();
        //2、给消费者配置对象添加参数
        properties.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,"hadoop100:9092");
        //配置序列化
        properties.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,StringDeserializer.class.getName());
        //配置消费者组（组名任意起名）必须
        properties.put(ConsumerConfig.GROUP_ID_CONFIG,"test");
        //创建消费者对象
        KafkaConsumer<String,String> kafkaConsumer=new KafkaConsumer<String, String>(properties);
        //注册要消费的主题
        ArrayList<String> topics=new ArrayList<>();
        topics.add("first");
        kafkaConsumer.subscribe(topics);
        while (true){
    
    
            //设置1s中消费一批数据
            ConsumerRecords<String,String> consumerRecords=kafkaConsumer.poll(Duration.ofSeconds(1));
            //打印消费到的数据
            for(ConsumerRecord<String,String> record:consumerRecords){
    
    
                System.out.println(record);
            }
        }
    }
}

Sent information

Consumption information (because I sent many times)

Independent Consumer Case

package com.longer.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.TopicPartition;
import org.apache.kafka.common.serialization.StringDeserializer;

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

public class CustomConsumerPartition {
    
    
    public static void main(String[] args) {
    
    
        Properties properties=new Properties();
        properties.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,"hadoop100:9092");
        properties.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,StringDeserializer.class.getName());
        //配置消费者组（组名任意起名）必须
        properties.put(ConsumerConfig.GROUP_ID_CONFIG,"test");
        KafkaConsumer kafkaConsumer=new KafkaConsumer(properties);
        //消费某个注意的某个分区数据
        ArrayList<TopicPartition> topicPartitions=new ArrayList<>();
        topicPartitions.add(new TopicPartition("first",0));
        kafkaConsumer.assign(topicPartitions);
        while (true){
    
    
            ConsumerRecords<String,String> consumerRecords=kafkaConsumer.poll(Duration.ofSeconds(1));
            for (ConsumerRecord<String, String> consumerRecord : consumerRecords) {
    
    
                System.out.println(consumerRecord);
            }
        }
    }
}

When sending information, it is found that only the information of partition 0 is consumed

Consumer Group Case

package com.longer.consumer.group;

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 CustomConsumer1 {
    
    
    public static void main(String[] args) {
    
    
        //创建消费者的配置对象
        Properties properties=new Properties();
        //2、给消费者配置对象添加参数
        properties.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,"hadoop100:9092");
        //配置序列化
        properties.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,StringDeserializer.class.getName());
        //配置消费者组（组名任意起名）必须
        properties.put(ConsumerConfig.GROUP_ID_CONFIG,"test");
        //创建消费者对象
        KafkaConsumer<String,String> kafkaConsumer=new KafkaConsumer<String, String>(properties);
        //注册要消费的主题
        ArrayList<String> topics=new ArrayList<>();
        topics.add("first");
        kafkaConsumer.subscribe(topics);
        while (true){
    
    
            //设置1s中消费一批数据
            ConsumerRecords<String,String> consumerRecords=kafkaConsumer.poll(Duration.ofSeconds(1));
            //打印消费到的数据
            for(ConsumerRecord<String,String> record:consumerRecords){
    
    
                System.out.println(record);
            }
        }
    }
}

Copy the three points, then run