序
本文主要解析一下spring for kafka对原生的kafka client consumer的封装与集成。
consumer工厂
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/core/DefaultKafkaConsumerFactory.java
protected KafkaConsumer<K, V> createKafkaConsumer(String clientIdSuffix) {
if (!this.configs.containsKey(ConsumerConfig.CLIENT_ID_CONFIG) || clientIdSuffix == null) {
return createKafkaConsumer();
}
else {
Map<String, Object> modifiedClientIdConfigs = new HashMap<>(this.configs);
modifiedClientIdConfigs.put(ConsumerConfig.CLIENT_ID_CONFIG,
modifiedClientIdConfigs.get(ConsumerConfig.CLIENT_ID_CONFIG) + clientIdSuffix);
return createKafkaConsumer(modifiedClientIdConfigs);
}
}
protected KafkaConsumer<K, V> createKafkaConsumer(Map<String, Object> configs) {
return new KafkaConsumer<K, V>(configs, this.keyDeserializer, this.valueDeserializer);
}ConcurrentKafkaListenerContainerFactory
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/config/ConcurrentKafkaListenerContainerFactory.java
关于consumer的主要的封装在ConcurrentKafkaListenerContainerFactory这个里头，本身的KafkaConsumer是线程不安全的，无法并发操作，这里spring又在包装了一层，根据配置的spring.kafka.listener.concurrency来生成多个并发的KafkaMessageListenerContainer实例
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/listener/ConcurrentMessageListenerContainer.java
public class ConcurrentMessageListenerContainer<K, V> extends AbstractMessageListenerContainer<K, V> {
private final ConsumerFactory<K, V> consumerFactory;
private final List<KafkaMessageListenerContainer<K, V>> containers = new ArrayList<>();
@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);
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);
container.start();
this.containers.add(container);
}
}
}
//......
} KafkaMessageListenerContainer
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/listener/KafkaMessageListenerContainer.java
public class KafkaMessageListenerContainer<K, V> extends AbstractMessageListenerContainer<K, V> {
private final ConsumerFactory<K, V> consumerFactory;
private final TopicPartitionInitialOffset[] topicPartitions;
private ListenerConsumer listenerConsumer;
private ListenableFuture<?> listenerConsumerFuture;
private GenericMessageListener<?> listener;
private GenericAcknowledgingMessageListener<?> acknowledgingMessageListener;
private String clientIdSuffix;
@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);
}
this.listenerConsumer = new ListenerConsumer(this.listener, this.acknowledgingMessageListener);
setRunning(true);
this.listenerConsumerFuture = containerProperties
.getConsumerTaskExecutor()
.submitListenable(this.listenerConsumer);
}
@Override
protected void doStop(final Runnable callback) {
if (isRunning()) {
this.listenerConsumerFuture.addCallback(new ListenableFutureCallback<Object>() {
@Override
public void onFailure(Throwable e) {
KafkaMessageListenerContainer.this.logger.error("Error while stopping the container: ", e);
if (callback != null) {
callback.run();
}
}
@Override
public void onSuccess(Object result) {
if (KafkaMessageListenerContainer.this.logger.isDebugEnabled()) {
KafkaMessageListenerContainer.this.logger
.debug(KafkaMessageListenerContainer.this + " stopped normally");
}
if (callback != null) {
callback.run();
}
}
});
setRunning(false);
this.listenerConsumer.consumer.wakeup();
}
}
//......
} 每个KafkaMessageListenerContainer都自己创建一个ListenerConsumer，然后自己创建一个独立的kafka consumer，每个ListenerConsumer在线程池里头运行，这样来实现并发。
每个ListenerConsumer里头都有一个recordsToProcess队列，从原始的kafka consumer poll出来的记录会放到这个队列里头，然后有一个ListenerInvoker线程循环超时等待从recordsToProcess取出记录，然后交给应用程序的KafkaListener标注的方法去执行
private final class ListenerInvoker implements SchedulingAwareRunnable {
private final CountDownLatch exitLatch = new CountDownLatch(1);
private volatile boolean active = true;
private volatile Thread executingThread;
ListenerInvoker() {
super();
}
@Override
public void run() {
Assert.isTrue(this.active, "This instance is not active anymore");
if (ListenerConsumer.this.theListener instanceof ConsumerSeekAware) {
((ConsumerSeekAware) ListenerConsumer.this.theListener).registerSeekCallback(ListenerConsumer.this);
}
try {
this.executingThread = Thread.currentThread();
while (this.active) {
try {
ConsumerRecords<K, V> records = ListenerConsumer.this.recordsToProcess.poll(1,
TimeUnit.SECONDS);
if (this.active) {
if (records != null) {
invokeListener(records);
}
else {
if (ListenerConsumer.this.logger.isTraceEnabled()) {
ListenerConsumer.this.logger.trace("No records to process");
}
}
}
}
catch (InterruptedException e) {
if (!this.active) {
Thread.currentThread().interrupt();
}
else {
ListenerConsumer.this.logger.debug("Interrupt ignored");
}
}
}
}
finally {
this.active = false;
this.exitLatch.countDown();
}
}
@Override
public boolean isLongLived() {
return true;
}
private void stop() {
if (ListenerConsumer.this.logger.isDebugEnabled()) {
ListenerConsumer.this.logger.debug("Stopping invoker");
}
this.active = false;
try {
if (!this.exitLatch.await(getContainerProperties().getShutdownTimeout(), TimeUnit.MILLISECONDS)
&& this.executingThread != null) {
if (ListenerConsumer.this.logger.isDebugEnabled()) {
ListenerConsumer.this.logger.debug("Interrupting invoker");
}
this.executingThread.interrupt();
}
}
catch (InterruptedException e) {
if (this.executingThread != null) {
this.executingThread.interrupt();
}
Thread.currentThread().interrupt();
}
if (ListenerConsumer.this.logger.isDebugEnabled()) {
ListenerConsumer.this.logger.debug("Invoker stopped");
}
}
}这里的invokeListener就是调用listener的onMessage方法
KafkaListener注解
这里我们来看看，标注KafkaListener的方法，最后是怎么包装成ListenerInvoker这个类里头调用的listener的
KafkaListenerAnnotationBeanPostProcessor
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/annotation/KafkaListenerAnnotationBeanPostProcessor.java
这个类会扫描bean的KafkaListener注解，然后将其信息注册到KafkaListenerEndpointRegistrar
@Override
public Object postProcessAfterInitialization(final Object bean, final String beanName) throws BeansException {
if (!this.nonAnnotatedClasses.contains(bean.getClass())) {
Class<?> targetClass = AopUtils.getTargetClass(bean);
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()) {
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) {
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);
}
}
this.registrar.registerEndpoint(endpoint, factory);
}KafkaListenerEndpointRegistrar
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/config/KafkaListenerEndpointRegistrar.java
/**
* Register a new {@link KafkaListenerEndpoint} alongside the
* {@link KafkaListenerContainerFactory} to use to create the underlying container.
* <p>The {@code factory} may be {@code null} if the default factory has to be
* used for that endpoint.
* @param endpoint the {@link KafkaListenerEndpoint} instance to register.
* @param factory the {@link KafkaListenerContainerFactory} to use.
*/
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);
}
}
}这里将KafkaListenerEndpoint包装为KafkaListenerEndpointDescriptor，注册到名为endpointDescriptors的KafkaListenerEndpointDescriptor集合中
KafkaListenerEndpointRegistrar
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/config/KafkaListenerEndpointRegistrar.java
public class KafkaListenerEndpointRegistrar implements BeanFactoryAware, InitializingBean {
@Override
public void afterPropertiesSet() {
registerAllEndpoints();
}
protected void registerAllEndpoints() {
synchronized (this.endpointDescriptors) {
for (KafkaListenerEndpointDescriptor descriptor : this.endpointDescriptors) {
this.endpointRegistry.registerListenerContainer(
descriptor.endpoint, resolveContainerFactory(descriptor));
}
this.startImmediately = true; // trigger immediate startup
}
}
}这个类实现了InitializingBean接口的afterPropertiesSet方法(
初始化bean的时候执行)，在这个里头去根据endpointDescriptors去挨个调用registerListenerContainer注册
KafkaListenerEndpointRegistry
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/config/KafkaListenerEndpointRegistry.java
public class KafkaListenerEndpointRegistry implements DisposableBean, SmartLifecycle, ApplicationContextAware,
ApplicationListener<ContextRefreshedEvent> {
protected final Log logger = LogFactory.getLog(getClass()); //NOSONAR
private final Map<String, MessageListenerContainer> listenerContainers =
new ConcurrentHashMap<String, MessageListenerContainer>();
//......
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 + "'");
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) {
startIfNecessary(container);
}
}
}
protected MessageListenerContainer createListenerContainer(KafkaListenerEndpoint endpoint,
KafkaListenerContainerFactory<?> factory) {
MessageListenerContainer listenerContainer = factory.createListenerContainer(endpoint);
if (listenerContainer instanceof InitializingBean) {
try {
((InitializingBean) listenerContainer).afterPropertiesSet();
}
catch (Exception ex) {
throw new BeanInitializationException("Failed to initialize message listener container", ex);
}
}
int containerPhase = listenerContainer.getPhase();
if (containerPhase < Integer.MAX_VALUE) { // a custom phase value
if (this.phase < Integer.MAX_VALUE && this.phase != containerPhase) {
throw new IllegalStateException("Encountered phase mismatch between container factory definitions: " +
this.phase + " vs " + containerPhase);
}
this.phase = listenerContainer.getPhase();
}
return listenerContainer;
}
@Override
public void start() {
for (MessageListenerContainer listenerContainer : getListenerContainers()) {
startIfNecessary(listenerContainer);
}
}
@Override
public void stop() {
for (MessageListenerContainer listenerContainer : getListenerContainers()) {
listenerContainer.stop();
}
}
} 注册的时候将endpoint转换为MessageListenerContainer，然后放到listenerContainers的map当中
AbstractKafkaListenerContainerFactory
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/config/AbstractKafkaListenerContainerFactory.java
public C createListenerContainer(KafkaListenerEndpoint endpoint) {
C instance = createContainerInstance(endpoint);
if (this.autoStartup != null) {
instance.setAutoStartup(this.autoStartup);
}
if (this.phase != null) {
instance.setPhase(this.phase);
}
if (this.applicationEventPublisher != null) {
instance.setApplicationEventPublisher(this.applicationEventPublisher);
}
if (endpoint.getId() != null) {
instance.setBeanName(endpoint.getId());
}
if (endpoint instanceof AbstractKafkaListenerEndpoint) {
AbstractKafkaListenerEndpoint<K, V> aklEndpoint = (AbstractKafkaListenerEndpoint<K, V>) endpoint;
if (this.recordFilterStrategy != null) {
aklEndpoint.setRecordFilterStrategy(this.recordFilterStrategy);
}
if (this.ackDiscarded != null) {
aklEndpoint.setAckDiscarded(this.ackDiscarded);
}
if (this.retryTemplate != null) {
aklEndpoint.setRetryTemplate(this.retryTemplate);
}
if (this.recoveryCallback != null) {
aklEndpoint.setRecoveryCallback(this.recoveryCallback);
}
if (this.batchListener != null) {
aklEndpoint.setBatchListener(this.batchListener);
}
}
endpoint.setupListenerContainer(instance, this.messageConverter);
initializeContainer(instance);
return instance;
}这里主要看这个setupMessageListener方法
spring-kafka-1.2.3.RELEASE-sources.jar!/org/springframework/kafka/config/AbstractKafkaListenerEndpoint.java
private void setupMessageListener(MessageListenerContainer container, MessageConverter messageConverter) {
Object messageListener = createMessageListener(container, messageConverter);
Assert.state(messageListener != null, "Endpoint [" + this + "] must provide a non null message listener");
if (this.retryTemplate != null) {
if (messageListener instanceof AcknowledgingMessageListener) {
messageListener = new RetryingAcknowledgingMessageListenerAdapter<>(
(AcknowledgingMessageListener<K, V>) messageListener, this.retryTemplate,
this.recoveryCallback);
}
else {
messageListener = new RetryingMessageListenerAdapter<>((MessageListener<K, V>) messageListener,
this.retryTemplate, (RecoveryCallback<Object>) this.recoveryCallback);
}
}
if (this.recordFilterStrategy != null) {
if (messageListener instanceof AcknowledgingMessageListener) {
messageListener = new FilteringAcknowledgingMessageListenerAdapter<>(
(AcknowledgingMessageListener<K, V>) messageListener, this.recordFilterStrategy,
this.ackDiscarded);
}
else if (messageListener instanceof MessageListener) {
messageListener = new FilteringMessageListenerAdapter<>((MessageListener<K, V>) messageListener,
this.recordFilterStrategy);
}
else if (messageListener instanceof BatchAcknowledgingMessageListener) {
messageListener = new FilteringBatchAcknowledgingMessageListenerAdapter<>(
(BatchAcknowledgingMessageListener<K, V>) messageListener, this.recordFilterStrategy,
this.ackDiscarded);
}
else if (messageListener instanceof BatchMessageListener) {
messageListener = new FilteringBatchMessageListenerAdapter<>(
(BatchMessageListener<K, V>) messageListener, this.recordFilterStrategy);
}
}
container.setupMessageListener(messageListener);
}这个messageListener包含了原始endpoint携带的bean以及method转换成的InvocableHandlerMethod，然后注入到MessageListenerContainer(
ConcurrentMessageListenerContainer)，然后这里就跟上头的ConcurrentMessageListenerContainer这个衔接上，根据配置的spring.kafka.listener.concurrency来生成多个并发的KafkaMessageListenerContainer实例
MethodKafkaListenerEndpoint
createMessageListener这个方法将endpoint包含的原始标注KafkaListener注解的bean以及方法，包装为InvocableHandlerMethod，注入到MessagingMessageListenerAdapter当中
public class MethodKafkaListenerEndpoint<K, V> extends AbstractKafkaListenerEndpoint<K, V> {
private Object bean;
private Method method;
private MessageHandlerMethodFactory messageHandlerMethodFactory;
//......
@Override
protected MessagingMessageListenerAdapter<K, V> createMessageListener(MessageListenerContainer container,
MessageConverter messageConverter) {
Assert.state(this.messageHandlerMethodFactory != null,
"Could not create message listener - MessageHandlerMethodFactory not set");
MessagingMessageListenerAdapter<K, V> messageListener = createMessageListenerInstance(messageConverter);
messageListener.setHandlerMethod(configureListenerAdapter(messageListener));
return messageListener;
}
/**
* Create a {@link HandlerAdapter} for this listener adapter.
* @param messageListener the listener adapter.
* @return the handler adapter.
*/
protected HandlerAdapter configureListenerAdapter(MessagingMessageListenerAdapter<K, V> messageListener) {
InvocableHandlerMethod invocableHandlerMethod =
this.messageHandlerMethodFactory.createInvocableHandlerMethod(getBean(), getMethod());
return new HandlerAdapter(invocableHandlerMethod);
}
} 这个类会将原始的bean跟方法包装为InvocableHandlerMethod这个类，然后注入到MessagingMessageListenerAdapter当中
小结
- 对于生产者来说，封装KafkaProducer到KafkaTemplate相对简单
-
对于消费者来说，由于spring是采用注解的形式去标注消息处理方法的，所以这里稍微费劲一点：
- 先在KafkaListenerAnnotationBeanPostProcessor中扫描bean，然后注册到KafkaListenerEndpointRegistrar
- 而KafkaListenerEndpointRegistrar在afterPropertiesSet的时候去创建MessageListenerContainer
- messageListener包含了原始endpoint携带的bean以及method转换成的InvocableHandlerMethod
- ConcurrentMessageListenerContainer这个衔接上，根据配置的spring.kafka.listener.concurrency来生成多个并发的KafkaMessageListenerContainer实例
- 每个KafkaMessageListenerContainer都自己创建一个ListenerConsumer，然后自己创建一个独立的kafka consumer，每个ListenerConsumer在线程池里头运行，这样来实现并发
- 每个ListenerConsumer里头都有一个recordsToProcess队列，从原始的kafka consumer poll出来的记录会放到这个队列里头，
- 然后有一个ListenerInvoker线程循环超时等待从recordsToProcess取出记录，然后调用messageListener的onMessage方法(
即KafkaListener注解标准的方法)
ListenerConsumer是重点，里头还有包括offset的提交，这里改天再详解一下。
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