spring-kafka源码解析
前言：
关于Kafka，是一个比较流行的MQ工具，也是多数公司比较常用的。有关于Kafka的一些基本内容读者可以参考官方文档，了解一下生产者消费者的使用。kafka的搭建笔者也不再详述，网络上有很多文章介绍。
这篇文章主要是从源码的角度来分析一下Spring对kafka的使用封装
笔者搭建的kafka版本为 kafka_2.11-0.11.0.1
1.原生的使用生产者、消费者
引入maven为：
org.apache.kafka
kafka-clients
0.10.1.1
1）生产者代码如下
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.Producer;
import org.apache.kafka.clients.producer.ProducerRecord;
import java.util.Properties;
public class KafkaProducerExample {
public static void main(String[] args) {
Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("acks", "all");
props.put("retries", 0);
props.put("batch.size", 16384);
props.put("linger.ms", 1);
props.put("buffer.memory", 33554432);
props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");
Producer producer = new KafkaProducer<>(props);
for(int i = 0; i < 100; i++)
producer.send(new ProducerRecord("test", "Hello"));
producer.close();
}
} 总结：通过以上可知，生产者比较简单，主要就是创建Producer，然后执行send方法即可
2）消费者代码如下
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import java.util.Arrays;
import java.util.Properties;
public class KafkaConsumerExample {
public static void main(String[] args) {
Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("group.id", "test");
props.put("enable.auto.commit", "true");
props.put("auto.commit.interval.ms", "1000");
props.put("session.timeout.ms", "30000");
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
KafkaConsumer consumer = new KafkaConsumer<>(props);
consumer.subscribe(Arrays.asList("test"));
while (true) {
ConsumerRecords records = consumer.poll(100);
for (ConsumerRecord record : records)
System.out.printf("offset = %d, key = %s, value = %s\n", record.offset(), record.key(), record.value());
}
}
} 总结：消费者主要就是通过KafkaConsumer.poll()方法拉取ConsumerRecords获取消费内容
2.Spring-kafka使用生产者、消费者
maven引入
org.springframework.kafka
spring-kafka
1.1.8.RELEASE
1）配置文件application.properties
spring.kafka.bootstrap-servers=localhost:9092
spring.kafka.producer.retries=0
spring.kafka.producer.batch-size=16384
spring.kafka.producer.buffer-memory=33554432
spring.kafka.producer.key-serializer=org.apache.kafka.common.serialization.StringSerializer
spring.kafka.producer.value-serializer=org.apache.kafka.common.serialization.StringSerializer
#=============== consumer =======================
spring.kafka.consumer.group-id=test-consumer-group
#spring.kafka.consumer.auto-offset-reset=earliest
spring.kafka.consumer.auto-offset-reset=latest
spring.kafka.consumer.enable-auto-commit=true
spring.kafka.consumer.auto-commit-interval=100
spring.kafka.consumer.key-deserializer=org.apache.kafka.common.serialization.StringDeserializer
spring.kafka.consumer.value-deserializer=org.apache.kafka.common.serialization.StringDeserializer2）创建PropsConfig类
@Configuration
@Data
public class PropsConfig {
@Value("${spring.kafka.bootstrap-servers}")
private String broker;
@Value("${spring.kafka.consumer.group-id}")
private String groupId;
@Value("${spring.kafka.consumer.auto-offset-reset}")
private String autoOffsetReset;
@Value("${spring.kafka.consumer.enable-auto-commit}")
private String enableAutoCommit;
}3）生产者代码
* 生产者KafkaTemplate创建，创建KafkaProducerConfig类，代码如下
@Configuration
@EnableKafka
public class KafkaProducerConfig {
@Autowired
PropsConfig propsConfig;
@Bean
public ProducerFactory producerFactory() {
return new DefaultKafkaProducerFactory<>(producerConfigs());
}
@Bean
public Map producerConfigs() {
Map props = new HashMap<>();
props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, propsConfig.getBroker());
props.put(ProducerConfig.RETRIES_CONFIG, 0);
props.put(ProducerConfig.BATCH_SIZE_CONFIG, 16384);
props.put(ProducerConfig.LINGER_MS_CONFIG, 1);
props.put(ProducerConfig.BUFFER_MEMORY_CONFIG, 33554432);
props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
return props;
}
@Bean
public KafkaTemplate kafkaTemplate() {
return new KafkaTemplate(producerFactory());
}
} * 生产者KafkaTemplate使用
@Component
public class ProducerServiceImpl implements ProducerService {
private static final Logger logger = LoggerFactory.getLogger(ProducerServiceImpl.class);
@Autowired
private KafkaTemplate template;
//发送消息方法
private void sendJson(String topic, String content) {
ListenableFuture> future = template.send(topic, content);
future.addCallback(new ListenableFutureCallback>() {
@Override
public void onSuccess(SendResult result) {
logger.info("msg OK. " + result.toString());
}
@Override
public void onFailure(Throwable ex) {
logger.error("msg send failed.", ex);
}
});
}
} 总结：生产者主要就是使用KafkaTemplate.send()方法来实现
2）消费者代码
* 创建消费者Config类，创建类KafkaConsumerConfig，代码如下
@Configuration
@EnableKafka
public class KafkaConsumerConfig {
@Autowired
PropsConfig propsConfig;// 配置文件对象
// 主要就是为了创建一下两个Factory
@Bean
KafkaListenerContainerFactory> kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory factory = new ConcurrentKafkaListenerContainerFactory<>();
factory.setConsumerFactory(consumerFactory());
factory.setConcurrency(4);
factory.setBatchListener(true);
factory.getContainerProperties().setPollTimeout(3000);
return factory;
}
@Bean
public ConsumerFactory consumerFactory() {
return new DefaultKafkaConsumerFactory<>(consumerConfigs());
}
@Bean
public Map consumerConfigs() {
Map propsMap = new HashMap<>();
propsMap.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, propsConfig.getBroker());
propsMap.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, propsConfig.getEnableAutoCommit());
propsMap.put(ConsumerConfig.AUTO_COMMIT_INTERVAL_MS_CONFIG, "100");
propsMap.put(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG, "15000");
propsMap.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
propsMap.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
propsMap.put(ConsumerConfig.GROUP_ID_CONFIG, propsConfig.getGroupId());
propsMap.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, propsConfig.getAutoOffsetReset());
propsMap.put(ConsumerConfig.MAX_POLL_RECORDS_CONFIG, 50);
return propsMap;
}
} * 创建Listener监听，主要是@KafkaListener
public class MyListener {
private static final String TPOIC = "test";
// 监听topic为test的0,1,2三个partition
@KafkaListener(id = "id0", topicPartitions = { @TopicPartition(topic = TPOIC, partitions = { "0","1","2" })})
public void listenPartition0(List> records) {
log.info("Id0 Listener, Thread ID: " + Thread.currentThread().getId());
log.info("Id0 records size " + records.size());
for (ConsumerRecord record : records) {
Optional kafkaMessage = Optional.ofNullable(record.value());
log.info("Received: " + record);
if (kafkaMessage.isPresent()) {
Object message = record.value();
String topic = record.topic();
log.info("p0 Received message={}", message);
}
}
}
} 总结：可以看到这里的消费者方式与传统的消费者方式有很大差异，下面我们主要来分析消费者的代码
3.Spring-kafka生产者源码分析
通过上面的分析可以看到，生产者主要就是KafkaTemplate.send()方法，下面我们就来分析一下这个方法
// KafkaTemplate.send(String topic, V data)
@Override
public ListenableFuture> send(String topic, V data) {
ProducerRecord producerRecord = new ProducerRecord<>(topic, data);// 这里同原生的使用是一致的，将消费封装为ProducerRecord
return doSend(producerRecord);// 主要在这里
}
// KafkaTemplate.doSend(final ProducerRecord producerRecord)
protected ListenableFuture> doSend(final ProducerRecord producerRecord) {
// 1.获取生产者
// this.producerFactory.createProducer()可以看到是通过工厂类来创建的
final Producer producer = getTheProducer();
if (this.logger.isTraceEnabled()) {
this.logger.trace("Sending: " + producerRecord);
}
final SettableListenableFuture> future = new SettableListenableFuture<>();
// 2.通过send方法发送数据，并调用回调方法
producer.send(producerRecord, new Callback() {
@Override
public void onCompletion(RecordMetadata metadata, Exception exception) {
try {
if (exception == null) {
future.set(new SendResult<>(producerRecord, metadata));
if (KafkaTemplate.this.producerListener != null
&& KafkaTemplate.this.producerListener.isInterestedInSuccess()) {
KafkaTemplate.this.producerListener.onSuccess(producerRecord.topic(),
producerRecord.partition(), producerRecord.key(), producerRecord.value(), metadata);
}
}
else {
future.setException(new KafkaProducerException(producerRecord, "Failed to send", exception));
if (KafkaTemplate.this.producerListener != null) {
KafkaTemplate.this.producerListener.onError(producerRecord.topic(),
producerRecord.partition(),
producerRecord.key(),
producerRecord.value(),
exception);
}
}
}
finally {
producer.close();
}
}
});
// 3.刷新
if (this.autoFlush) {
flush();
}
if (this.logger.isTraceEnabled()) {
this.logger.trace("Sent: " + producerRecord);
}
return future;
} 总结：发送的方法比较简单，就是简单的通过Producer.send()来发送消息，同原生的方式基本没有区别
4.Spring-kafka消费者源码分析
消费者的实现比较隐蔽，我们主观能看到的就是两个注解@EnableKafka和@KafkaListener
按照Spring的一贯风格那就应该是这两个注解实现的，下面我们来看下这两个注解，首先来分析@EnableKafka
1）@EnableKafka注解分析
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(KafkaBootstrapConfiguration.class)// 主要功能就是倒入一个类，我们来看下这个类
public @interface EnableKafka {
}
// KafkaBootstrapConfiguration
@Configuration
public class KafkaBootstrapConfiguration {
@SuppressWarnings("rawtypes")
@Bean(name = KafkaListenerConfigUtils.KAFKA_LISTENER_ANNOTATION_PROCESSOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public KafkaListenerAnnotationBeanPostProcessor kafkaListenerAnnotationProcessor() {
return new KafkaListenerAnnotationBeanPostProcessor();
}
@Bean(name = KafkaListenerConfigUtils.KAFKA_LISTENER_ENDPOINT_REGISTRY_BEAN_NAME)
public KafkaListenerEndpointRegistry defaultKafkaListenerEndpointRegistry() {
return new KafkaListenerEndpointRegistry();
}
}总结：可以看到KafkaBootstrapConfiguration的主要功能也就是创建两个bean
* KafkaListenerAnnotationBeanPostProcessor，注解如下
从注解可知，其主要功能就是监听@KafkaListener注解（我们重点分析这个类）
/**
* Bean post-processor that registers methods annotated with {@link KafkaListener}
* to be invoked by a Kafka message listener container created under the covers
* by a {@link org.springframework.kafka.config.KafkaListenerContainerFactory}
* according to the parameters of the annotation.
*
* Annotated methods can use flexible arguments as defined by {@link KafkaListener}.
* KafkaListenerEndpointRegistry，注解如下
可知，其主要功能就是为KafkaListenerEndpoint接口管理MessageListenerContainer，我们暂时没用到这个功能，故先不分析
有兴趣的读者可以参考这篇博客：http://www.cnblogs.com/huangfox/p/9798446.html 里面是其一个应用场景
/**
* Creates the necessary {@link MessageListenerContainer} instances for the
* registered {@linkplain KafkaListenerEndpoint endpoints}. Also manages the
* lifecycle of the listener containers, in particular within the lifecycle
* of the application context.5.KafkaListenerAnnotationBeanPostProcessor的分析
类结构如下：
public class KafkaListenerAnnotationBeanPostProcessor
implements BeanPostProcessor, Ordered, BeanFactoryAware, SmartInitializingSingleton { 关于BeanPostProcessor，我们并不陌生，在之前的Spring源码系列分析中，实现这个接口的类，会实现其postProcessAfterInitialization（）方法，可用来修改bean对象，如果读者想对该接口有进一步了解，可参考：https://blog.csdn.net/elim168/article/details/76146351
1）KafkaListenerAnnotationBeanPostProcessor.postProcessAfterInitialization()方法分析
@Override
public Object postProcessAfterInitialization(final Object bean, final String beanName) throws BeansException {
if (!this.nonAnnotatedClasses.contains(bean.getClass())) {
// 1.获取bean对应的Class
Class targetClass = AopUtils.getTargetClass(bean);
// 2.查找类是否有@KafkaListener注解（本例中类没有相关注解）
Collection classLevelListeners = findListenerAnnotations(targetClass);
final boolean hasClassLevelListeners = classLevelListeners.size() > 0;
final List multiMethods = new ArrayList();
// 3.查找类中方法上是否有对应的@KafkaListener注解，本例中是注解再方法上的
Map> annotatedMethods = MethodIntrospector.selectMethods(targetClass,
new MethodIntrospector.MetadataLookup>() {
@Override
public Set inspect(Method method) {
Set listenerMethods = findListenerAnnotations(method);
return (!listenerMethods.isEmpty() ? listenerMethods : null);
}
});
if (hasClassLevelListeners) {
Set methodsWithHandler = MethodIntrospector.selectMethods(targetClass,
new ReflectionUtils.MethodFilter() {
@Override
public boolean matches(Method method) {
return AnnotationUtils.findAnnotation(method, KafkaHandler.class) != null;
}
});
multiMethods.addAll(methodsWithHandler);
}
// 4.annotatedMethods不为空，直接走else逻辑
if (annotatedMethods.isEmpty()) {
this.nonAnnotatedClasses.add(bean.getClass());
if (this.logger.isTraceEnabled()) {
this.logger.trace("No @KafkaListener annotations found on bean type: " + bean.getClass());
}
}
else {
// Non-empty set of methods
for (Map.Entry> entry : annotatedMethods.entrySet()) {
Method method = entry.getKey();
for (KafkaListener listener : entry.getValue()) {
// 主要逻辑就在这，处理方法上的@KafkaListener，接下来我们单独分析这个方法
processKafkaListener(listener, method, bean, beanName);
}
}
if (this.logger.isDebugEnabled()) {
this.logger.debug(annotatedMethods.size() + " @KafkaListener methods processed on bean '"
+ beanName + "': " + annotatedMethods);
}
}
if (hasClassLevelListeners) {
processMultiMethodListeners(classLevelListeners, multiMethods, bean, beanName);
}
}
return bean;
} 2）KafkaListenerAnnotationBeanPostProcessor.processKafkaListener(listener, method, bean, beanName);
protected void processKafkaListener(KafkaListener kafkaListener, Method method, Object bean, String beanName) {
Method methodToUse = checkProxy(method, bean);
MethodKafkaListenerEndpoint endpoint = new MethodKafkaListenerEndpoint();
endpoint.setMethod(methodToUse);
endpoint.setBeanFactory(this.beanFactory);
// 主要功能在这里
processListener(endpoint, kafkaListener, bean, methodToUse, beanName);
}
// processListener()
protected void processListener(MethodKafkaListenerEndpoint endpoint, KafkaListener kafkaListener, Object bean,
Object adminTarget, String beanName) {
// 1.封装Endpoint
endpoint.setBean(bean);
endpoint.setMessageHandlerMethodFactory(this.messageHandlerMethodFactory);
endpoint.setId(getEndpointId(kafkaListener));
endpoint.setTopicPartitions(resolveTopicPartitions(kafkaListener));
endpoint.setTopics(resolveTopics(kafkaListener));
endpoint.setTopicPattern(resolvePattern(kafkaListener));
String group = kafkaListener.group();
if (StringUtils.hasText(group)) {
Object resolvedGroup = resolveExpression(group);
if (resolvedGroup instanceof String) {
endpoint.setGroup((String) resolvedGroup);
}
}
// 2.我们可以主动指定@KafkaListener的containerFactory，在本例中，我们没有主动指定
KafkaListenerContainerFactory factory = null;
String containerFactoryBeanName = resolve(kafkaListener.containerFactory());
if (StringUtils.hasText(containerFactoryBeanName)) {
Assert.state(this.beanFactory != null, "BeanFactory must be set to obtain container factory by bean name");
try {
factory = this.beanFactory.getBean(containerFactoryBeanName, KafkaListenerContainerFactory.class);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanInitializationException("Could not register Kafka listener endpoint on [" + adminTarget
+ "] for bean " + beanName + ", no " + KafkaListenerContainerFactory.class.getSimpleName()
+ " with id '" + containerFactoryBeanName + "' was found in the application context", ex);
}
}
// 将endpoint注册到registrar，我们继续看下这个方法
this.registrar.registerEndpoint(endpoint, factory);
}
//KafkaListenerEndpointRegistrar.registerEndpoint()
public void registerEndpoint(KafkaListenerEndpoint endpoint, KafkaListenerContainerFactory factory) {
Assert.notNull(endpoint, "Endpoint must be set");
Assert.hasText(endpoint.getId(), "Endpoint id must be set");
// 1.将endpoint封装为KafkaListenerEndpointDescriptor
KafkaListenerEndpointDescriptor descriptor = new KafkaListenerEndpointDescriptor(endpoint, factory);
synchronized (this.endpointDescriptors) {
if (this.startImmediately) { // Register and start immediately
this.endpointRegistry.registerListenerContainer(descriptor.endpoint,
resolveContainerFactory(descriptor), true);
}
else {
// 将descriptor添加到endpointDescriptors
// List endpointDescriptors = new ArrayList<>();
this.endpointDescriptors.add(descriptor);
}
}
} 一连串的分析，我们最终得到一个含有KafkaListener基本信息的Endpoint，最后Endpoint被封装到KafkaListenerEndpointDescriptor，KafkaListenerEndpointDescriptor被添加到KafkaListenerEndpointRegistrar.endpointDescriptors中，也就是一个list中，结束了。
那么放到这个list的后续处理呢？
我们可以看下这个KafkaListenerEndpointRegistrar的类结构
public class KafkaListenerEndpointRegistrar implements BeanFactoryAware, InitializingBean {实现了InitializingBean接口，这个接口中有一个afterPropertiesSet（）方法，会在类加载完成之后自动执行，那么我们来看下这个方法
3）KafkaListenerEndpointRegistrar.afterPropertiesSet()初始化方法
@Override
public void afterPropertiesSet() {
registerAllEndpoints();
}
protected void registerAllEndpoints() {
synchronized (this.endpointDescriptors) {
// 遍历descriptor中的每一个KafkaListenerEndpointDescriptor，并执行对应的方法
for (KafkaListenerEndpointDescriptor descriptor : this.endpointDescriptors) {
// 关键在这里
this.endpointRegistry.registerListenerContainer(
descriptor.endpoint, resolveContainerFactory(descriptor));
}
this.startImmediately = true; // trigger immediate startup
}
}
// KafkaListenerEndpointRegistry.registerListenerContainer()
public void registerListenerContainer(KafkaListenerEndpoint endpoint, KafkaListenerContainerFactory factory) {
registerListenerContainer(endpoint, factory, false);
}
@SuppressWarnings("unchecked")
public void registerListenerContainer(KafkaListenerEndpoint endpoint, KafkaListenerContainerFactory factory,
boolean startImmediately) {
Assert.notNull(endpoint, "Endpoint must not be null");
Assert.notNull(factory, "Factory must not be null");
String id = endpoint.getId();
Assert.hasText(id, "Endpoint id must not be empty");
synchronized (this.listenerContainers) {
Assert.state(!this.listenerContainers.containsKey(id),
"Another endpoint is already registered with id '" + id + "'");
// 1.创建Endpoint对应的MessageListenerContainer，将创建好的MessageListenerContainer放入listenerContainers
MessageListenerContainer container = createListenerContainer(endpoint, factory);
this.listenerContainers.put(id, container);
// 2.如果我们的KafkaListener注解中有对应的group信息，则将container添加到对应的group中
if (StringUtils.hasText(endpoint.getGroup()) && this.applicationContext != null) {
List containerGroup;
if (this.applicationContext.containsBean(endpoint.getGroup())) {
containerGroup = this.applicationContext.getBean(endpoint.getGroup(), List.class);
}
else {
containerGroup = new ArrayList();
this.applicationContext.getBeanFactory().registerSingleton(endpoint.getGroup(), containerGroup);
}
containerGroup.add(container);
}
// 3.startImmediately默认为false，则不执行start方法
if (startImmediately) {
startIfNecessary(container);
}
}
} 我们将创建Container的方法单独拎出来介绍
4）KafkaListenerEndpointRegistry.createListenerContainer(endpoint, factory);
protected MessageListenerContainer createListenerContainer(KafkaListenerEndpoint endpoint,
KafkaListenerContainerFactory factory) {
// 主要在这里，通过工厂来创建Container
MessageListenerContainer listenerContainer = factory.createListenerContainer(endpoint);
...
return listenerContainer;
}
// AbstractKafkaListenerContainerFactory.createListenerContainer()
public C createListenerContainer(KafkaListenerEndpoint endpoint) {
// 重点在这里
C instance = createContainerInstance(endpoint);
// 一系列设置参数的动作
...
// 初始化Container的"topics", "topicPartitions", "topicPattern","messageListener", "ackCount", "ackTime"等参数
endpoint.setupListenerContainer(instance, this.messageConverter);
initializeContainer(instance);
return instance;
}
// 默认ConcurrentKafkaListenerContainerFactory.createContainerInstance()
// 由该方法可知，最终创建的容器是ConcurrentMessageListenerContainer，根据用户设定的参数
protected ConcurrentMessageListenerContainer createContainerInstance(KafkaListenerEndpoint endpoint) {
Collection topicPartitions = endpoint.getTopicPartitions();
if (!topicPartitions.isEmpty()) {
ContainerProperties properties = new ContainerProperties(
topicPartitions.toArray(new TopicPartitionInitialOffset[topicPartitions.size()]));
return new ConcurrentMessageListenerContainer(getConsumerFactory(), properties);
}
else {
Collection topics = endpoint.getTopics();
if (!topics.isEmpty()) {
ContainerProperties properties = new ContainerProperties(topics.toArray(new String[topics.size()]));
return new ConcurrentMessageListenerContainer(getConsumerFactory(), properties);
}
else {
ContainerProperties properties = new ContainerProperties(endpoint.getTopicPattern());
return new ConcurrentMessageListenerContainer(getConsumerFactory(), properties);
}
}
} 总结：经过以上一些列的分析，我们@KafkaListener注解变为ConcurrentMessageListenerContainer类，这个Container中包含了我们所需要的topic相关信息
6.ConcurrentMessageListenerContainer的源码分析
类结构如下：
其实现了Lifecycle接口，Lifecycle是一个神奇的接口，它定义了对象的生命周期方法，任何Spring管理的对象都可以实现这个借口，当ApplicationContext自身启动和停止时，它会自动调动上下文中所有生命周期的实现。更多关于Lifecycle的内容可参考：https://www.cnblogs.com/wade-luffy/p/6074088.html
所以可以知道：ConcurrentMessageListenerContainer在容器初始化完成时候会自动调用start()方法
1）ConcurrentMessageListenerContainer.start()
// AbstractMessageListenerContainer.start()
@Override
public final void start() {
synchronized (this.lifecycleMonitor) {
if (!isRunning()) {
Assert.isTrue(
this.containerProperties.getMessageListener() instanceof KafkaDataListener,
"A " + GenericMessageListener.class.getName() + " implementation must be provided");
// 直接调用子类的doStart()方法
doStart();
}
}
}
// ConcurrentMessageListenerContainer.doStart()
@Override
protected void doStart() {
if (!isRunning()) {
ContainerProperties containerProperties = getContainerProperties();
TopicPartitionInitialOffset[] topicPartitions = containerProperties.getTopicPartitions();
// 1.将concurrency设置为topicPartitions大小，本例中我们的consumer监听3个分片
if (topicPartitions != null
&& this.concurrency > topicPartitions.length) {
this.logger.warn("When specific partitions are provided, the concurrency must be less than or "
+ "equal to the number of partitions; reduced from " + this.concurrency + " to "
+ topicPartitions.length);
this.concurrency = topicPartitions.length;
}
setRunning(true);
// 2.根据分片数创建KafkaMessageListenerContainer，每一个分片创建一个Container
for (int i = 0; i < this.concurrency; i++) {
KafkaMessageListenerContainer container;
if (topicPartitions == null) {
container = new KafkaMessageListenerContainer<>(this.consumerFactory, containerProperties);
}
else {
container = new KafkaMessageListenerContainer<>(this.consumerFactory, containerProperties,
partitionSubset(containerProperties, i));
}
if (getBeanName() != null) {
container.setBeanName(getBeanName() + "-" + i);
}
if (getApplicationEventPublisher() != null) {
container.setApplicationEventPublisher(getApplicationEventPublisher());
}
container.setClientIdSuffix("-" + i);
// 3.启动Container，并添加其到containers中
// 重点就在这个start方法，启动了KafkaMessageListenerContainer，下面单独来分析
container.start();
this.containers.add(container);
}
}
} 2）KafkaMessageListenerContainer.start()方法分析
@Override
public final void start() {
synchronized (this.lifecycleMonitor) {
if (!isRunning()) {
Assert.isTrue(
this.containerProperties.getMessageListener() instanceof KafkaDataListener,
"A " + GenericMessageListener.class.getName() + " implementation must be provided");
// 直接调用子类KafkaMessageListenerContainer.doStart()方法
doStart();
}
}
}
// KafkaMessageListenerContainer.doStart()
@Override
protected void doStart() {
// 1.如果已启动，则直接返回
if (isRunning()) {
return;
}
ContainerProperties containerProperties = getContainerProperties();
...
// 2.获取对应的监听类，本例中就是MyListener，被包装到BatchMessagingMessageListenerAdapter中
Object messageListener = containerProperties.getMessageListener();
Assert.state(messageListener != null, "A MessageListener is required");
if (messageListener instanceof GenericAcknowledgingMessageListener) {
// 2.1 将监听类MyListener赋值到acknowledgingMessageListener
this.acknowledgingMessageListener = (GenericAcknowledgingMessageListener) messageListener;
}
else if (messageListener instanceof GenericMessageListener) {
this.listener = (GenericMessageListener) messageListener;
}
...
// 3.根据this.listener, this.acknowledgingMessageListener创建对应的listenerConsumer
this.listenerConsumer = new ListenerConsumer(this.listener, this.acknowledgingMessageListener);
setRunning(true);
// 4.最后一步，将listenerConsumer作为一个任务提交
this.listenerConsumerFuture = containerProperties
.getConsumerTaskExecutor()
.submitListenable(this.listenerConsumer);
}总结：看到这里，可以看出，最终将我们@KafkaListener中的topicPartitions
@KafkaListener(id = "id0", topicPartitions = { @TopicPartition(topic = TPOIC, partitions = { "0","1","2" })})转换为ListenerConsumer，每一个partition生成一个ListenerConsumer
7.ListenerConsumer的工作
ListenerConsumer是一个私有类，在KafkaMessageListenerContainer类里面，类结构如下（可知，其实现了一个Runnable接口）
1）主要成员变量及构造方法
private final class ListenerConsumer implements SchedulingAwareRunnable, ConsumerSeekCallback {
private final ContainerProperties containerProperties = getContainerProperties();
private final OffsetCommitCallback commitCallback = this.containerProperties.getCommitCallback() != null
? this.containerProperties.getCommitCallback()
: new LoggingCommitCallback();
// 都是一些比较熟悉的属性，关键是这个consumer，主要的消费功能就是它来实现的
private final Consumer consumer;
private final Map> offsets = new HashMap>();
private final boolean autoCommit = KafkaMessageListenerContainer.this.consumerFactory.isAutoCommit();
...
// 下面来看一下ListenerConsumer的构造方法
@SuppressWarnings("unchecked")
ListenerConsumer(GenericMessageListener listener, GenericAcknowledgingMessageListener ackListener) {
Assert.state(!this.isAnyManualAck || !this.autoCommit,
"Consumer cannot be configured for auto commit for ackMode " + this.containerProperties.getAckMode());
this.theListener = listener == null ? ackListener : listener;
// 1.最终要的方法，构造Consumer
final Consumer consumer = KafkaMessageListenerContainer.this.consumerFactory.createConsumer(
this.consumerGroupId, KafkaMessageListenerContainer.this.clientIdSuffix);
this.consumer = consumer;
ConsumerRebalanceListener rebalanceListener = createRebalanceListener(consumer);
// 2.subscribe对应的topic
if (KafkaMessageListenerContainer.this.topicPartitions == null) {
if (this.containerProperties.getTopicPattern() != null) {
consumer.subscribe(this.containerProperties.getTopicPattern(), rebalanceListener);
}
else {
consumer.subscribe(Arrays.asList(this.containerProperties.getTopics()), rebalanceListener);
}
}
// 3.或者assign给定的partition
else {
List topicPartitions =
Arrays.asList(KafkaMessageListenerContainer.this.topicPartitions);
this.definedPartitions = new HashMap<>(topicPartitions.size());
for (TopicPartitionInitialOffset topicPartition : topicPartitions) {
this.definedPartitions.put(topicPartition.topicPartition(),
new OffsetMetadata(topicPartition.initialOffset(), topicPartition.isRelativeToCurrent()));
}
consumer.assign(new ArrayList<>(this.definedPartitions.keySet()));
}
...
} 总结：通过构造方法，ListenerConsumer完成了Consumer的创建以及topic和partition的监听
2）run()方法，主要业务实现方法
@Override
public void run() {
this.consumerThread = Thread.currentThread();
if (this.theListener instanceof ConsumerSeekAware) {
((ConsumerSeekAware) this.theListener).registerSeekCallback(this);
}
if (this.transactionManager != null) {
ProducerFactoryUtils.setConsumerGroupId(this.consumerGroupId);
}
this.count = 0;
this.last = System.currentTimeMillis();
if (isRunning() && this.definedPartitions != null) {
initPartitionsIfNeeded();
}
long lastReceive = System.currentTimeMillis();
long lastAlertAt = lastReceive;
// 不停轮询实现topic的消费
while (isRunning()) {
try {
if (!this.autoCommit && !this.isRecordAck) {
processCommits();
}
processSeeks();
// 1.使用poll方法拉取数据
ConsumerRecords records = this.consumer.poll(this.containerProperties.getPollTimeout());
this.lastPoll = System.currentTimeMillis();
if (records != null && this.logger.isDebugEnabled()) {
this.logger.debug("Received: " + records.count() + " records");
}
// 2.获取到数据后执行监听器的回调方法
if (records != null && records.count() > 0) {
if (this.containerProperties.getIdleEventInterval() != null) {
lastReceive = System.currentTimeMillis();
}
// 回调在此
invokeListener(records);
}
else {
if (this.containerProperties.getIdleEventInterval() != null) {
long now = System.currentTimeMillis();
if (now > lastReceive + this.containerProperties.getIdleEventInterval()
&& now > lastAlertAt + this.containerProperties.getIdleEventInterval()) {
publishIdleContainerEvent(now - lastReceive);
lastAlertAt = now;
if (this.theListener instanceof ConsumerSeekAware) {
seekPartitions(getAssignedPartitions(), true);
}
}
}
}
}
...
}
...
}
//invokeListener(records);
private void invokeListener(final ConsumerRecords records) {
if (this.isBatchListener) {
invokeBatchListener(records);
}
else {
invokeRecordListener(records);
}
}
...
// 一层层追踪下来最终到了
private RuntimeException doInvokeRecordListener(final ConsumerRecord record,
@SuppressWarnings("rawtypes") Producer producer) throws Error {
try {
if (this.acknowledgingMessageListener != null) {
// 最终实现在这里，即调用BatchMessagingMessageListenerAdapter.onMessage方法
// BatchMessagingMessageListenerAdapter是一个包装类，包装了真正需要调用的类和对应方法
// 在本例中就是MyListener.listenPartition0()方法，至此，消费就结束了
this.acknowledgingMessageListener.onMessage(record,
this.isAnyManualAck
? new ConsumerAcknowledgment(record)
: null);
}
else {
this.listener.onMessage(record);
}
ackCurrent(record, producer);
}
...
return null;
}
总结：
1）@EnableKafka注解引入KafkaListenerAnnotationBeanPostProcessor类
2）KafkaListenerAnnotationBeanPostProcessor类监听所有带有@KafkaListener注解的类或方法
3）将每一个带有@KafkaListener注解的类或方法封装为一个MethodKafkaListenerEndpoint
4）将KafkaListenerEndpoint和对应的KafkaListenerContainerFactory封装到一个KafkaListenerEndpointDescriptor中，并将其添加到KafkaListenerEndpointRegistrar.endpointDescriptors中
5）遍历每一个KafkaListenerEndpointDescriptor，为其创建一个MessageListenerContainer，在本例中具体实现类为ConcurrentMessageListenerContainer
6）ConcurrentMessageListenerContainer在ApplicationContext创建完成之后，自动调用其start方法，start方法会根据我们在@KafkaListener中设置的topic和分片数来创建对应数量的KafkaMessageListenerContainer，并调用其start方法
7）KafkaMessageListenerContainer.start()方法会创建一个ListenerConsumer，ListenerConsumer是一个Runnable接口实现类
8）ListenerConsumer在构造的时候会创建一个Consumer，并assign对应的topic和partitions，然后执行一个while循环，在循环中不停的执行consumer.poll()方法拉取数据，并回调@KafkaListener对应的方法
至此，Spring-kafka的消费者代码分析结束。