首先通过@EnableKafka注解，注入KafkaBootstrapConfiguration类
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
// @Import是spring提供的注入类的方式
@Import(KafkaBootstrapConfiguration.class)
public @interface EnableKafka {
}
再注入KafkaListenerAnnotationBeanPostProcessor
@Configuration
public class KafkaBootstrapConfiguration {
@SuppressWarnings("rawtypes")
@Bean(name = KafkaListenerConfigUtils.KAFKA_LISTENER_ANNOTATION_PROCESSOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public KafkaListenerAnnotationBeanPostProcessor kafkaListenerAnnotationProcessor() {
// 注入KafkaListenerAnnotationBeanPostProcessor
return new KafkaListenerAnnotationBeanPostProcessor();
}
@Bean(name = KafkaListenerConfigUtils.KAFKA_LISTENER_ENDPOINT_REGISTRY_BEAN_NAME)
public KafkaListenerEndpointRegistry defaultKafkaListenerEndpointRegistry() {
return new KafkaListenerEndpointRegistry();
}
}
可以看到KafkaListenerAnnotationBeanPostProcessor实现了BeanPostProcessor，那自然存在postProcessBeforeInitialization和postProcessAfterInitialization两个关键方法
public class KafkaListenerAnnotationBeanPostProcessor<K, V>
implements BeanPostProcessor, Ordered, BeanFactoryAware, SmartInitializingSingleton {
// 代码省略...
}
@Override
public Object postProcessAfterInitialization(final Object bean, final String beanName) throws BeansException {
if (!this.nonAnnotatedClasses.contains(bean.getClass())) {
Class<?> targetClass = AopUtils.getTargetClass(bean);
//收集注解方法
Collection<KafkaListener> classLevelListeners = findListenerAnnotations(targetClass);
final boolean hasClassLevelListeners = classLevelListeners.size() > 0;
final List<Method> multiMethods = new ArrayList<Method>();
Map<Method, Set<KafkaListener>> annotatedMethods = MethodIntrospector.selectMethods(targetClass,
new MethodIntrospector.MetadataLookup<Set<KafkaListener>>() {
@Override
public Set<KafkaListener> inspect(Method method) {
Set<KafkaListener> listenerMethods = findListenerAnnotations(method);
return (!listenerMethods.isEmpty() ? listenerMethods : null);
}
});
if (hasClassLevelListeners) {
Set<Method> methodsWithHandler = MethodIntrospector.selectMethods(targetClass,
new ReflectionUtils.MethodFilter() {
@Override
public boolean matches(Method method) {
return AnnotationUtils.findAnnotation(method, KafkaHandler.class) != null;
}
});
multiMethods.addAll(methodsWithHandler);
}
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<Method, Set<KafkaListener>> entry : annotatedMethods.entrySet()) {
Method method = entry.getKey();
for (KafkaListener listener : entry.getValue()) {
//遍历处理
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;
}
protected void processKafkaListener(KafkaListener kafkaListener, Method method, Object bean, String beanName) {
Method methodToUse = checkProxy(method, bean);
MethodKafkaListenerEndpoint<K, V> endpoint = new MethodKafkaListenerEndpoint<K, V>();
endpoint.setMethod(methodToUse);
endpoint.setBeanFactory(this.beanFactory);
processListener(endpoint, kafkaListener, bean, methodToUse, beanName);
}
protected void processListener(MethodKafkaListenerEndpoint<?, ?> endpoint, KafkaListener kafkaListener, Object bean,
Object adminTarget, String beanName) {
//把kafkaListener中的属性封装成对象
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.containerGroup();
if (StringUtils.hasText(group)) {
Object resolvedGroup = resolveExpression(group);
if (resolvedGroup instanceof String) {
endpoint.setGroup((String) resolvedGroup);
}
}
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);
}
}
//交给KafkaListenerEndpointRegistry处理
this.registrar.registerEndpoint(endpoint, factory);
}
public void registerEndpoint(KafkaListenerEndpoint endpoint, KafkaListenerContainerFactory<?> factory) {
Assert.notNull(endpoint, "Endpoint must be set");
Assert.hasText(endpoint.getId(), "Endpoint id must be set");
// Factory may be null, we defer the resolution right before actually creating the container
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 {
this.endpointDescriptors.add(descriptor);
}
}
}
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 + "'");
//创建ConcurrentMessageListenerContainer
MessageListenerContainer container = createListenerContainer(endpoint, factory);
this.listenerContainers.put(id, container);
if (StringUtils.hasText(endpoint.getGroup()) && this.applicationContext != null) {
List<MessageListenerContainer> containerGroup;
if (this.applicationContext.containsBean(endpoint.getGroup())) {
containerGroup = this.applicationContext.getBean(endpoint.getGroup(), List.class);
}
else {
containerGroup = new ArrayList<MessageListenerContainer>();
this.applicationContext.getBeanFactory().registerSingleton(endpoint.getGroup(), containerGroup);
}
containerGroup.add(container);
}
if (startImmediately) {
//开启监听入口
startIfNecessary(container);
}
}
}
private void startIfNecessary(MessageListenerContainer listenerContainer) {
if (this.contextRefreshed || listenerContainer.isAutoStartup()) {
listenerContainer.start();
}
}
@Override
public final void start() {
synchronized (this.lifecycleMonitor) {
Assert.isTrue(
this.containerProperties.getMessageListener() instanceof KafkaDataListener,
"A " + KafkaDataListener.class.getName() + " implementation must be provided");
doStart();
}
}
@Override
protected void doStart() {
if (!isRunning()) {
ContainerProperties containerProperties = getContainerProperties();
TopicPartitionInitialOffset[] topicPartitions = containerProperties.getTopicPartitions();
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);
//根据主题中的分区数和concurrency数计算，决定创建多少KafkaMessageListenerContainer，也就是开启多少线程
for (int i = 0; i < this.concurrency; i++) {
KafkaMessageListenerContainer<K, V> 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);
//KafkaMessageListenerContainer的doStart()
container.start();
this.containers.add(container);
}
}
}
@Override
protected void doStart() {
if (isRunning()) {
return;
}
ContainerProperties containerProperties = getContainerProperties();
if (!this.consumerFactory.isAutoCommit()) {
AckMode ackMode = containerProperties.getAckMode();
if (ackMode.equals(AckMode.COUNT) || ackMode.equals(AckMode.COUNT_TIME)) {
Assert.state(containerProperties.getAckCount() > 0, "'ackCount' must be > 0");
}
if ((ackMode.equals(AckMode.TIME) || ackMode.equals(AckMode.COUNT_TIME))
&& containerProperties.getAckTime() == 0) {
containerProperties.setAckTime(5000);
}
}
Object messageListener = containerProperties.getMessageListener();
Assert.state(messageListener != null, "A MessageListener is required");
if (messageListener instanceof GenericAcknowledgingMessageListener) {
this.acknowledgingMessageListener = (GenericAcknowledgingMessageListener<?>) messageListener;
}
else if (messageListener instanceof GenericMessageListener) {
this.listener = (GenericMessageListener<?>) messageListener;
}
else {
throw new IllegalStateException("messageListener must be 'MessageListener' "
+ "or 'AcknowledgingMessageListener', not " + messageListener.getClass().getName());
}
if (containerProperties.getConsumerTaskExecutor() == null) {
SimpleAsyncTaskExecutor consumerExecutor = new SimpleAsyncTaskExecutor(
(getBeanName() == null ? "" : getBeanName()) + "-C-");
containerProperties.setConsumerTaskExecutor(consumerExecutor);
}
if (containerProperties.getListenerTaskExecutor() == null) {
SimpleAsyncTaskExecutor listenerExecutor = new SimpleAsyncTaskExecutor(
(getBeanName() == null ? "" : getBeanName()) + "-L-");
containerProperties.setListenerTaskExecutor(listenerExecutor);
}
//创建ListenerConsumer
this.listenerConsumer = new ListenerConsumer(this.listener, this.acknowledgingMessageListener);
setRunning(true);
//开启ListenerConsumer线程
this.listenerConsumerFuture = containerProperties
.getConsumerTaskExecutor()
.submitListenable(this.listenerConsumer);
}
@Override
public void run() {
if (this.theListener instanceof ConsumerSeekAware) {
((ConsumerSeekAware) this.theListener).registerSeekCallback(this);
}
this.count = 0;
this.last = System.currentTimeMillis();
if (isRunning() && this.definedPartitions != null) {
initPartitionsIfNeeded();
// we start the invoker here as there will be no rebalance calls to
// trigger it, but only if the container is not set to autocommit
// otherwise we will process records on a separate thread
if (!this.autoCommit) {
startInvoker();
}
}
long lastReceive = System.currentTimeMillis();
long lastAlertAt = lastReceive;
while (isRunning()) {
try {
if (!this.autoCommit) {
processCommits();
}
processSeeks();
if (this.logger.isTraceEnabled()) {
this.logger.trace("Polling (paused=" + this.paused + ")...");
}
//拉取消息
ConsumerRecords<K, V> records = this.consumer.poll(this.containerProperties.getPollTimeout());
if (records != null && this.logger.isDebugEnabled()) {
this.logger.debug("Received: " + records.count() + " records");
}
if (records != null && records.count() > 0) {
if (this.containerProperties.getIdleEventInterval() != null) {
lastReceive = System.currentTimeMillis();
}
// if the container is set to auto-commit, then execute in the
// same thread
// otherwise send to the buffering queue
if (this.autoCommit) {
//自动提交直接反射调用@kafkaListener注解的方法
invokeListener(records);
}
else {
//非自动提交把消息放入队列中
if (sendToListener(records)) {
if (this.assignedPartitions != null) {
// avoid group management rebalance due to a slow
// consumer
this.consumer.pause(this.assignedPartitions);
this.paused = true;
this.unsent = 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);
}
}
}
}
this.unsent = checkPause(this.unsent);
}
catch (WakeupException e) {
this.unsent = checkPause(this.unsent);
}
catch (Exception e) {
if (this.containerProperties.getGenericErrorHandler() != null) {
this.containerProperties.getGenericErrorHandler().handle(e, null);
}
else {
this.logger.error("Container exception", e);
}
}
}
if (this.listenerInvokerFuture != null) {
stopInvoker();
commitManualAcks();
}
try {
this.consumer.unsubscribe();
}
catch (WakeupException e) {
// No-op. Continue process
}
this.consumer.close();
if (this.logger.isInfoEnabled()) {
this.logger.info("Consumer stopped");
}
}
源码内容比较多，只截图主流程的业务，有兴趣可以了解过主流程后再细看。
