kafka原理、安装、java版开发

• kafka原理介绍
  待补充…
  1、写入流程

1）producer先从zookeeper的 "/brokers/…/state"节点找到该partition的leader
2）producer将消息发送给该leader
3）leader将消息写入本地log
4）followers从leader pull消息，写入本地log后向leader发送ACK
5）leader收到所有ISR中的replication的ACK后，增加HW（high watermark，最后commit 的offset）并向producer发送ACK
2、保存策略
无论消息是否被消费，kafka 都会保留所有消息。有两种策略可以删除旧数据：
基于时间：log.retention.hours=168
基于大小：log.retention.bytes=1073741824
3、消费
消息由生产者发布到Kafka集群后，会被消费者消费。消息的消费模型有两种：推送模型（push）和拉取模型（pull）。
(1)同一个消费组内 ，消息只能被消费一次。同一个patition同一时间只能被一个组内消费者消费，如果广播设置多个消费者组。消息生产到多个patition中，起到负载均衡作用。

问题：
使用消息队列不可能是单机的（必然是分布式or集群）

Kafka天然是分布式的，往一个topic丢数据，实际上就是往多个broker的partition存储数据

数据写到消息队列，可能会存在数据丢失问题，数据在消息队列需要持久化(磁盘？数据库？Redis？分布式文件系统？)

Kafka会将partition以消息日志的方式(落磁盘)存储起来，通过 顺序访问IO和缓存(等到一定的量或时间)才真正把数据写到磁盘上，来提高速度。

想要保证消息（数据）是有序的，怎么做？

Kafka会将数据写到partition，单个partition的写入是有顺序的。如果要保证全局有序，那只能写入一个partition中。如果要消费也有序，消费者也只能有一个。

为什么在消息队列中重复消费了数据

凡是分布式就无法避免网络抖动/机器宕机等问题的发生，很有可能消费者A读取了数据，还没来得及消费，就挂掉了。Zookeeper发现消费者A挂了，让消费者B去消费原本消费者A的分区，等消费者A重连的时候，发现已经重复消费同一条数据了。(各种各样的情况，消费者超时等等都有可能…)

如果业务上不允许重复消费的问题，最好消费者那端做业务上的校验（如果已经消费过了，就不消费了）

• kafka安装
  环境：docker、docker-compose

version: '2'
services:
  zookeeper:
    image: zookeeper
    ports:
      - "2181:2181"
  kafka:
    image: wurstmeister/kafka
    ports:
      - "9092:9092"
    environment:
      KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://192.168.29.131:9092
      KAFKA_ADVERTISED_HOST_NAME: 192.168.29.131
      KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
  kafka-manager:
    image: sheepkiller/kafka-manager:latest
    restart: always
    container_name: kafa-manager
    hostname: kafka-manager
    ports:
      - "9002:9000"
    links:            # 连接本compose文件创建的container
      - kafka
      - zookeeper
    environment:
      ZK_HOSTS: zookeeper:2181
      KAFKA_BROKERS: kafka:9092
      APPLICATION_SECRET: letmein
      KM_ARGS: -Djava.net.preferIPv4Stack=true

• kafka开发
  配置文件：application.yml

server:
  port: 8080
  servlet:
    context-path: /
spring:
  kafka:
    bootstrap-servers: 192.168.29.131:9092
    producer:
      retries: 0
      batch-size: 16384
      buffer-memory: 33554432
      key-serializer: org.apache.kafka.common.serialization.StringSerializer
      value-serializer: org.apache.kafka.common.serialization.StringSerializer
    consumer:
      group-id: service-kafka
      # 手动提交
      enable-auto-commit: false
      auto-offset-reset: latest
      key-deserializer: org.apache.kafka.common.serialization.StringDeserializer
      value-deserializer: org.apache.kafka.common.serialization.StringDeserializer
      properties:
        session.timeout.ms: 60000
    listener:
      log-container-config: false
      concurrency: 5
      # 手动提交
      ack-mode: manual_immediate

pom.xml文件

<!--kafka-->
        <dependency>
            <groupId>org.springframework.kafka</groupId>
            <artifactId>spring-kafka</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        
        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
        </dependency>

        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
        </dependency>

java代码
生产者

package com.wqq.service.config;

import com.wqq.service.constants.KafkaConsts;
import lombok.AllArgsConstructor;
import org.springframework.boot.autoconfigure.kafka.KafkaProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.annotation.EnableKafka;
import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
import org.springframework.kafka.core.*;
import org.springframework.kafka.listener.ContainerProperties;

@Configuration
@EnableConfigurationProperties({KafkaProperties.class})
@EnableKafka
@AllArgsConstructor
public class KafkaConfig {
    private final KafkaProperties kafkaProperties;

    @Bean
    public KafkaTemplate<String, String> kafkaTemplate() {
        return new KafkaTemplate<>(producerFactory());
    }

    @Bean
    public ProducerFactory<String, String> producerFactory() {
        return new DefaultKafkaProducerFactory<>(kafkaProperties.buildProducerProperties());
    }

    @Bean
    public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactory() {
        ConcurrentKafkaListenerContainerFactory<String, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(consumerFactory());
        factory.setConcurrency(KafkaConsts.DEFAULT_PARTITION_NUM);
        factory.setBatchListener(true);
        factory.getContainerProperties().setPollTimeout(3000);
        return factory;
    }

    @Bean
    public ConsumerFactory<String, String> consumerFactory() {
        return new DefaultKafkaConsumerFactory<>(kafkaProperties.buildConsumerProperties());
    }

    @Bean("ackContainerFactory")
    public ConcurrentKafkaListenerContainerFactory<String, String> ackContainerFactory() {
        ConcurrentKafkaListenerContainerFactory<String, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(consumerFactory());
        factory.getContainerProperties().setAckMode(ContainerProperties.AckMode.MANUAL_IMMEDIATE);
        factory.setConcurrency(KafkaConsts.DEFAULT_PARTITION_NUM);
        return factory;
    }

}

package com.wqq.service.constants;

public interface KafkaConsts {
    /**
     * 默认分区大小
     */
    Integer DEFAULT_PARTITION_NUM = 3;

    /**
     * Topic 名称
     */
    String TOPIC_TEST = "test";
}

package com.wqq.service;

import com.wqq.service.constants.KafkaConsts;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.kafka.core.KafkaTemplate;

@SpringBootTest
class ServiceKafkaApplicationTests {

    @Autowired
    private KafkaTemplate<String, String> kafkaTemplate;

    /**
     * 测试发送消息
     */
    @Test
    public void testSend() throws Exception{
        kafkaTemplate.send(KafkaConsts.TOPIC_TEST, "hello,kafka...");
    }
}

消费者

package com.wqq.service.handler;

import com.wqq.service.constants.KafkaConsts;
import lombok.extern.slf4j.Slf4j;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.kafka.support.Acknowledgment;
import org.springframework.stereotype.Component;

@Component
@Slf4j
public class MessageHandler {

    @KafkaListener(topics = KafkaConsts.TOPIC_TEST, containerFactory = "ackContainerFactory")
    public void handleMessage(ConsumerRecord record, Acknowledgment acknowledgment) {
        try {
            String message = (String) record.value();
            log.info("收到消息: {}", message);
        } catch (Exception e) {
            log.error(e.getMessage(), e);
        } finally {
            // 手动提交 offset
            acknowledgment.acknowledge();
        }
    }
}