@KafkaListener和KafkaTemplate自动装配原理分析

依赖项和配置信息参见另一篇博文@KafkaListener的配置使用，这里主要借助源码分析@KafkaListener和KafkaTemplate自动装配原理。

1、KafkaAutoConfiguration 源码分析

KafkaAutoConfiguration类自动装配生成了生产者客户端KafkaTemplate的bean和消费者基础ConsumerFactory的bean，KafkaAutoConfiguration导入KafkaAnnotationDrivenConfiguration，KafkaAnnotationDrivenConfiguration最终生成了ConcurrentKafkaListenerContainerFactory的bean, 该bean是@KafkaListener默认使用的容器工厂，即指定了消费的kafka集群。

package org.springframework.boot.autoconfigure.kafka;

import java.io.IOException;
import org.springframework.beans.factory.ObjectProvider;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.kafka.core.ConsumerFactory;
import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
import org.springframework.kafka.core.DefaultKafkaProducerFactory;
import org.springframework.kafka.core.KafkaAdmin;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.core.ProducerFactory;
import org.springframework.kafka.security.jaas.KafkaJaasLoginModuleInitializer;
import org.springframework.kafka.support.LoggingProducerListener;
import org.springframework.kafka.support.ProducerListener;
import org.springframework.kafka.support.converter.RecordMessageConverter;
import org.springframework.kafka.transaction.KafkaTransactionManager;

@Configuration(
    proxyBeanMethods = false
)
/// KafkaTemplate在类路径下存在时，加载该配置类
@ConditionalOnClass({
   
   KafkaTemplate.class})  
@EnableConfigurationProperties({
   
   KafkaProperties.class})
/// 将KafkaAnnotationDrivenConfiguration、KafkaStreamsAnnotationDrivenConfiguration配置类合并过来
@Import({
   
   KafkaAnnotationDrivenConfiguration.class, KafkaStreamsAnnotationDrivenConfiguration.class})  
public class KafkaAutoConfiguration {
   
   

    private final KafkaProperties properties;

    public KafkaAutoConfiguration(KafkaProperties properties) {
   
   
        this.properties = properties;
    }

    @Bean  
    /// KafkaTemplate的bean未定义时，自动生成该bean
    @ConditionalOnMissingBean({
   
   KafkaTemplate.class})
    public KafkaTemp