kafka原理和实践（四）spring-kafka消费者源码

Posted on 2017-11-30 12:31 只会一点java 阅读(26221) 评论(7) 编辑收藏举报

系列目录

kafka原理和实践（一）原理：10分钟入门

kafka原理和实践（二）spring-kafka简单实践

kafka原理和实践（三）spring-kafka生产者源码

kafka原理和实践（四）spring-kafka消费者源码

kafka原理和实践（五）spring-kafka配置详解

kafka原理和实践（六）总结升华

==============正文分割线=====================

一、kafkaConsumer消费者模型

如上图所示，spring-kafka消费者模型主要流程：

1.容器启动，轮询执行消费。

2.kafkaConsumer拉取消息流程：

1）Fetcher请求获取器获取请求并存储在unset中

2）ConsumerNetworkClient网络客户端执行poll(),调用NetWlrikClient的send()方法从unset中获取ClientRequest请求转成RequestSend最终塞进Selector的KafkaChannel通道中，Seletcor.send()从kafka集群拉取待消费数据ConsumerRecords

3. 消费者监听器MessageListener.onMessage()执行用户自定义的实际消费业务逻辑。

一、kafkaConsumer构造

  1 @SuppressWarnings("unchecked")
  2     private KafkaConsumer(ConsumerConfig config,
  3                           Deserializer<K> keyDeserializer,
  4                           Deserializer<V> valueDeserializer) {
  5         try {
  6             log.debug("Starting the Kafka consumer");
  7             this.requestTimeoutMs = config.getInt(ConsumerConfig.REQUEST_TIMEOUT_MS_CONFIG);
  8             int sessionTimeOutMs = config.getInt(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG);
  9             int fetchMaxWaitMs = config.getInt(ConsumerConfig.FETCH_MAX_WAIT_MS_CONFIG);
 10             if (this.requestTimeoutMs <= sessionTimeOutMs || this.requestTimeoutMs <= fetchMaxWaitMs)
 11                 throw new ConfigException(ConsumerConfig.REQUEST_TIMEOUT_MS_CONFIG + " should be greater than " + ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG + " and " + ConsumerConfig.FETCH_MAX_WAIT_MS_CONFIG);
 12             this.time = new SystemTime();
 13 
 14             String clientId = config.getString(ConsumerConfig.CLIENT_ID_CONFIG);
 15             if (clientId.length() <= 0)
 16                 clientId = "consumer-" + CONSUMER_CLIENT_ID_SEQUENCE.getAndIncrement();
 17             this.clientId = clientId;
 18             Map<String, String> metricsTags = new LinkedHashMap<>();
 19             metricsTags.put("client-id", clientId);
 20             MetricConfig metricConfig = new MetricConfig().samples(config.getInt(ConsumerConfig.METRICS_NUM_SAMPLES_CONFIG))
 21                     .timeWindow(config.getLong(ConsumerConfig.METRICS_SAMPLE_WINDOW_MS_CONFIG), TimeUnit.MILLISECONDS)
 22                     .tags(metricsTags);
 23             List<MetricsReporter> reporters = config.getConfiguredInstances(ConsumerConfig.METRIC_REPORTER_CLASSES_CONFIG,
 24                     MetricsReporter.class);
 25             reporters.add(new JmxReporter(JMX_PREFIX));
 26             this.metrics = new Metrics(metricConfig, reporters, time);
 27             this.retryBackoffMs = config.getLong(ConsumerConfig.RETRY_BACKOFF_MS_CONFIG);
 28 
 29             // load interceptors and make sure they get clientId
 30             Map<String, Object> userProvidedConfigs = config.originals();
 31             userProvidedConfigs.put(ConsumerConfig.CLIENT_ID_CONFIG, clientId);
 32             List<ConsumerInterceptor<K, V>> interceptorList = (List) (new ConsumerConfig(userProvidedConfigs)).getConfiguredInstances(ConsumerConfig.INTERCEPTOR_CLASSES_CONFIG,
 33                     ConsumerInterceptor.class);
 34             this.interceptors = interceptorList.isEmpty() ? null : new ConsumerInterceptors<>(interceptorList);
 35             if (keyDeserializer == null) {
 36                 this.keyDeserializer = config.getConfiguredInstance(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
 37                         Deserializer.class);
 38                 this.keyDeserializer.configure(config.originals(), true);
 39             } else {
 40                 config.ignore(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG);
 41                 this.keyDeserializer = keyDeserializer;
 42             }
 43             if (valueDeserializer == null) {
 44                 this.valueDeserializer = config.getConfiguredInstance(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
 45                         Deserializer.class);
 46                 this.valueDeserializer.configure(config.originals(), false);
 47             } else {
 48                 config.ignore(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG);
 49                 this.valueDeserializer = valueDeserializer;
 50             }
 51             ClusterResourceListeners clusterResourceListeners = configureClusterResourceListeners(keyDeserializer, valueDeserializer, reporters, interceptorList);
 52             this.metadata = new Metadata(retryBackoffMs, config.getLong(ConsumerConfig.METADATA_MAX_AGE_CONFIG), false, clusterResourceListeners);
 53             List<InetSocketAddress> addresses = ClientUtils.parseAndValidateAddresses(config.getList(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG));
 54             this.metadata.update(Cluster.bootstrap(addresses), 0);
 55             String metricGrpPrefix = "consumer";
 56             ChannelBuilder channelBuilder = ClientUtils.createChannelBuilder(config.values());
 57             NetworkClient netClient = new NetworkClient(
 58                     new Selector(config.getLong(ConsumerConfig.CONNECTIONS_MAX_IDLE_MS_CONFIG), metrics, time, metricGrpPrefix, channelBuilder),
 59                     this.metadata,
 60                     clientId,
 61                     100, // a fixed large enough value will suffice
 62                     config.getLong(ConsumerConfig.RECONNECT_BACKOFF_MS_CONFIG),
 63                     config.getInt(ConsumerConfig.SEND_BUFFER_CONFIG),
 64                     config.getInt(ConsumerConfig.RECEIVE_BUFFER_CONFIG),
 65                     config.getInt(ConsumerConfig.REQUEST_TIMEOUT_MS_CONFIG), time);
 66             this.client = new ConsumerNetworkClient(netClient, metadata, time, retryBackoffMs,
 67                     config.getInt(ConsumerConfig.REQUEST_TIMEOUT_MS_CONFIG));
 68             OffsetResetStrategy offsetResetStrategy = OffsetResetStrategy.valueOf(config.getString(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG).toUpperCase(Locale.ROOT));
 69             this.subscriptions = new SubscriptionState(offsetResetStrategy);
 70             List<PartitionAssignor> assignors = config.getConfiguredInstances(
 71                     ConsumerConfig.PARTITION_ASSIGNMENT_STRATEGY_CONFIG,
 72                     PartitionAssignor.class);
 73             this.coordinator = new ConsumerCoordinator(this.client,
 74                     config.getString(ConsumerConfig.GROUP_ID_CONFIG),
 75                     config.getInt(ConsumerConfig.MAX_POLL_INTERVAL_MS_CONFIG),
 76                     config.getInt(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG),
 77                     config.getInt(ConsumerConfig.HEARTBEAT_INTERVAL_MS_CONFIG),
 78                     assignors,
 79                     this.metadata,
 80                     this.subscriptions,
 81                     metrics,
 82                     metricGrpPrefix,
 83                     this.time,
 84                     retryBackoffMs,
 85                     new ConsumerCoordinator.DefaultOffsetCommitCallback(),
 86                     config.getBoolean(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG),
 87                     config.getInt(ConsumerConfig.AUTO_COMMIT_INTERVAL_MS_CONFIG),
 88                     this.interceptors,
 89                     config.getBoolean(ConsumerConfig.EXCLUDE_INTERNAL_TOPICS_CONFIG));
 90             this.fetcher = new Fetcher<>(this.client,
 91                     config.getInt(ConsumerConfig.FETCH_MIN_BYTES_CONFIG),
 92                     config.getInt(ConsumerConfig.FETCH_MAX_BYTES_CONFIG),
 93                     config.getInt(ConsumerConfig.FETCH_MAX_WAIT_MS_CONFIG),
 94                     config.getInt(ConsumerConfig.MAX_PARTITION_FETCH_BYTES_CONFIG),
 95                     config.getInt(ConsumerConfig.MAX_POLL_RECORDS_CONFIG),
 96                     config.getBoolean(ConsumerConfig.CHECK_CRCS_CONFIG),
 97                     this.keyDeserializer,
 98                     this.valueDeserializer,
 99                     this.metadata,
100                     this.subscriptions,
101                     metrics,
102                     metricGrpPrefix,
103                     this.time,
104                     this.retryBackoffMs);
105 
106             config.logUnused();
107             AppInfoParser.registerAppInfo(JMX_PREFIX, clientId);
108 
109             log.debug("Kafka consumer created");
110         } catch (Throwable t) {
111             // call close methods if internal objects are already constructed
112             // this is to prevent resource leak. see KAFKA-2121
113             close(true);
114             // now propagate the exception
115             throw new KafkaException("Failed to construct kafka consumer", t);
116         }
117     }

从KafkaConsumer构造函数来看，核心组件有：

1.Metadata：封装了元数据的一些逻辑的类。元数据仅保留一个主题的子集，随着时间的推移可以添加。当我们请求一个主题的元数据时，我们没有任何元数据会触发元数据更新。如果对元数据启用了主题过期，那么在更新之后，在过期时间间隔内未使用的任何主题都将从元数据刷新集中删除。

2.ConsumerNetworkClient：高等级消费者访问网络层，为请求Future任务提供基本支持。这个类是线程安全的，但是不提供响应回调的同步。这保证在调用它们时不会持有锁。

3.SubscriptionState：订阅的TopicPartition的offset状态维护

4.ConsumerCoordinator：消费者的协调者，负责partitiion的分配，reblance

5.Fetcher：从brokers上按照配置获取消息。

二、消费者容器启动流程

kafka消费者有两种常见的实现方式：

1.xml配置文件

2.基于注解实现

其实，不管哪种方式，本质只是生成Spring Bean的方式不同而已。我们就以xml的实现方式来追踪源码。

基于xml的总体配置如下：

 1 <!-- 1.定义consumer的参数 -->
 2     <bean id="consumerProperties" class="java.util.HashMap">
 3         <constructor-arg>
 4             <map>
 5                 <entry key="bootstrap.servers" value="${bootstrap.servers}" />
 6                 <entry key="group.id" value="${group.id}" />
 7                 <entry key="enable.auto.commit" value="${enable.auto.commit}" />
 8                 <entry key="session.timeout.ms" value="${session.timeout.ms}" />
 9                 <entry key="key.deserializer"
10                     value="org.apache.kafka.common.serialization.StringDeserializer" />
11                 <entry key="value.deserializer"
12                     value="org.apache.kafka.common.serialization.StringDeserializer" />
13             </map>
14         </constructor-arg>
15     </bean>
16 
17     <!-- 2.创建consumerFactory bean -->
18     <bean id="consumerFactory"
19         class="org.springframework.kafka.core.DefaultKafkaConsumerFactory" >
20         <constructor-arg>
21             <ref bean="consumerProperties" />
22         </constructor-arg>
23     </bean>
24 
25     <!-- 3.定义消费实现类 -->
26     <bean id="kafkaConsumerService" class="xxx.service.impl.KafkaConsumerSerivceImpl" />
27 
28     <!-- 4.消费者容器配置信息 -->
29     <bean id="containerProperties" class="org.springframework.kafka.listener.config.ContainerProperties">
30         <!-- topic -->
31         <constructor-arg name="topics">
32             <list>
33                 <value>${kafka.consumer.topic.credit.for.lease}</value>
34                 <value>${loan.application.feedback.topic}</value>
35                 <value>${templar.agreement.feedback.topic}</value>
36                 <value>${templar.aggrement.active.feedback.topic}</value>
37                 <value>${templar.aggrement.agreementRepaid.topic}</value>
38                 <value>${templar.aggrement.agreementWithhold.topic}</value>
39                 <value>${templar.aggrement.agreementRepayRemind.topic}</value>
40             </list>
41         </constructor-arg>
42         <property name="messageListener" ref="kafkaConsumerService" />
43     </bean>
44     <!-- 5.消费者并发消息监听容器，执行doStart()方法 -->
45     <bean id="messageListenerContainer" class="org.springframework.kafka.listener.ConcurrentMessageListenerContainer" init-method="doStart" >
46         <constructor-arg ref="consumerFactory" />
47         <constructor-arg ref="containerProperties" />
48         <property name="concurrency" value="${concurrency}" />
49     </bean>

分为5个步骤：

2.1.定义消费参数bean

consumerProperties ,就是个map<key,value>

2.2.创建consumerFactory bean

DefaultKafkaConsumerFactory 实现了ConsumerFactory接口，提供创建消费者和判断是否自动提交2个方法。通过consumerProperties作为参数构造。

1 public interface ConsumerFactory<K, V> {
2 
3     Consumer<K, V> createConsumer();
4 
5     boolean isAutoCommit();
6 
7 
8 }

2.3.定义消费实现类

自定义一个类实现MessageListener接口，接口设计如下：

实现onMessage方法，去消费接收到的消息。两种方案：

1）MessageListener 消费完消息后自动提交offset(enable.auto.commit=true时),可提高效率，存在消费失败但移动了偏移量的风险。

2）AcknowledgingMessageListener 消费完消息后手动提交offset(enable.auto.commit=false时)效率降低，无消费失败但移动偏移量的风险。

2.4.监听容器配置信息

ContainerProperties：包含了一个监听容器的运行时配置信息，主要定义了监听的主题、分区、初始化偏移量，还有消息监听器。

  1 public class ContainerProperties {
  2 
  3     private static final int DEFAULT_SHUTDOWN_TIMEOUT = 10000;
  4 
  5     private static final int DEFAULT_QUEUE_DEPTH = 1;
  6 
  7     private static final int DEFAULT_PAUSE_AFTER = 10000;
  8 
  9     /**
 10      * Topic names.监听的主题字符串数组
 11      */
 12     private final String[] topics;
 13 
 14     /**
 15      * Topic pattern.监听的主题模板
 16      */
 17     private final Pattern topicPattern;
 18 
 19     /**
 20      * Topics/partitions/initial offsets.
 21      */
 22     private final TopicPartitionInitialOffset[] topicPartitions;
 23 
 24     /**
 25      * 确认模式（自动确认属性为false时使用）
 26      * <ul>
 27      * <li>1.RECORD逐条确认: 每条消息被发送给监听者后确认</li>
 28      * <li>2.BATCH批量确认: 当批量消息记录被消费者接收到并传送给监听器时确认</li>
 30      * <li>3.TIME超时确认:当超过设置的超时时间毫秒数时确认(should be greater than
 31      * {@code #setPollTimeout(long) pollTimeout}.</li>
 32      * <li>4.COUNT计数确认: 当接收到指定数量之后确认</li>
 33      * <li>5.MANUAL手动确认：由监听器负责确认（AcknowledgingMessageListener）</ul>
 36      */
 37     private AbstractMessageListenerContainer.AckMode ackMode = AckMode.BATCH;
 38 
 39     /**
 40      * The number of outstanding record count after which offsets should be
 41      * committed when {@link AckMode#COUNT} or {@link AckMode#COUNT_TIME} is being
 42      * used.
 43      */
 44     private int ackCount;
 45 
 46     /**
 47      * The time (ms) after which outstanding offsets should be committed when
 48      * {@link AckMode#TIME} or {@link AckMode#COUNT_TIME} is being used. Should be
 49      * larger than
 50      */
 51     private long ackTime;
 52 
 53     /**
 54      * 消息监听器，必须是 MessageListener或者AcknowledgingMessageListener两者中的一个 55      * 56      */
 57     private Object messageListener;
 58 
 59     /**
 60      * The max time to block in the consumer waiting for records.
 61      */
 62     private volatile long pollTimeout = 1000;
 63 
 64     /**
 65      * 线程执行器：轮询消费者
 66      */
 67     private AsyncListenableTaskExecutor consumerTaskExecutor;
 68 
 69     /**
 70      * 线程执行器：调用监听器
 71      */
 72     private AsyncListenableTaskExecutor listenerTaskExecutor;
 73 
 74     /**
 75      * 错误回调，当监听器抛出异常时
 76      */
 77     private GenericErrorHandler<?> errorHandler;
 78 
 79     /**
 80      * When using Kafka group management and {@link #setPauseEnabled(boolean)} is
 81      * true, the delay after which the consumer should be paused. Default 10000.
 82      */
 83     private long pauseAfter = DEFAULT_PAUSE_AFTER;
 84 
 85     /**
 86      * When true, avoids rebalancing when this consumer is slow or throws a
 87      * qualifying exception - pauses the consumer. Default: true.
 88      * @see #pauseAfter
 89      */
 90     private boolean pauseEnabled = true;
 91 
 92     /**
 93      * Set the queue depth for handoffs from the consumer thread to the listener
 94      * thread. Default 1 (up to 2 in process).
 95      */
 96     private int queueDepth = DEFAULT_QUEUE_DEPTH;
 97 
 98     /**
 99      * 停止容器超时时间    */
103     private long shutdownTimeout = DEFAULT_SHUTDOWN_TIMEOUT;
104 
105     /**
106      * 用户定义的消费者再平衡监听器实现类     */
108     private ConsumerRebalanceListener consumerRebalanceListener;
109 
110     /**
111      * 提交回调，默认记录日志。      */
114     private OffsetCommitCallback commitCallback;
115 
116     /**
117      * Whether or not to call consumer.commitSync() or commitAsync() when the
118      * container is responsible for commits. Default true. See
119      * https://github.com/spring-projects/spring-kafka/issues/62 At the time of
120      * writing, async commits are not entirely reliable.
121      */
122     private boolean syncCommits = true;
123 
124     private boolean ackOnError = true;
125 
126     private Long idleEventInterval;
127 
128     public ContainerProperties(String... topics) {
129         Assert.notEmpty(topics, "An array of topicPartitions must be provided");
130         this.topics = Arrays.asList(topics).toArray(new String[topics.length]);
131         this.topicPattern = null;
132         this.topicPartitions = null;
133     }
134 
135     public ContainerProperties(Pattern topicPattern) {
136         this.topics = null;
137         this.topicPattern = topicPattern;
138         this.topicPartitions = null;
139     }
140 
141     public ContainerProperties(TopicPartitionInitialOffset... topicPartitions) {
142         this.topics = null;
143         this.topicPattern = null;
144         Assert.notEmpty(topicPartitions, "An array of topicPartitions must be provided");
145         this.topicPartitions = new LinkedHashSet<>(Arrays.asList(topicPartitions))
146                 .toArray(new TopicPartitionInitialOffset[topicPartitions.length]);
147     }
148 ...省略各种set、get
149 
150 }

2.5.启动并发消息监听容器

核心类ConcurrentMessageListenerContainer,继承自抽象类AbstractMessageListenerContainer，类图如下：

看上图可知AbstractMessageListenerContainer有2个实现类分别对应单线程和多线程，建议采用多线程消费。下面分析一下主要ConcurrentMessageListenerContainer类，注意2个方法：

1.构造函数，入参：消费者工厂ConsumerFactory+容器配置ContainerProperties

2.doStart()：核心方法KafkaMessageListenerContainer的start()方法。源码如下：

  1 public class ConcurrentMessageListenerContainer<K, V> extends AbstractMessageListenerContainer<K, V> {
  2 
  3     private final ConsumerFactory<K, V> consumerFactory;
  4 
  5     private final List<KafkaMessageListenerContainer<K, V>> containers = new ArrayList<>();
  6 
  7     private int concurrency = 1;
  8 
  9     /**
 10      * Construct an instance with the supplied configuration properties.
 11      * The topic partitions are distributed evenly across the delegate
 12      * {@link KafkaMessageListenerContainer}s.
 13      * @param consumerFactory the consumer factory.
 14      * @param containerProperties the container properties.
 15      */
 16     public ConcurrentMessageListenerContainer(ConsumerFactory<K, V> consumerFactory,
 17             ContainerProperties containerProperties) {
 18         super(containerProperties);
 19         Assert.notNull(consumerFactory, "A ConsumerFactory must be provided");
 20         this.consumerFactory = consumerFactory;
 21     }
 22 
 23     public int getConcurrency() {
 24         return this.concurrency;
 25     }
 26 
 27     /**
 28      * The maximum number of concurrent {@link KafkaMessageListenerContainer}s running.
 29      * Messages from within the same partition will be processed sequentially.
 30      * @param concurrency the concurrency.
 31      */
 32     public void setConcurrency(int concurrency) {
 33         Assert.isTrue(concurrency > 0, "concurrency must be greater than 0");
 34         this.concurrency = concurrency;
 35     }
 36 
 37     /**
 38      * Return the list of {@link KafkaMessageListenerContainer}s created by
 39      * this container.
 40      * @return the list of {@link KafkaMessageListenerContainer}s created by
 41      * this container.
 42      */
 43     public List<KafkaMessageListenerContainer<K, V>> getContainers() {
 44         return Collections.unmodifiableList(this.containers);
 45     }
 46 
 47     /*
 48      * Under lifecycle lock.
 49      */
 50     @Override
 51     protected void doStart() {
 52         if (!isRunning()) {
 53             ContainerProperties containerProperties = getContainerProperties();
 54             TopicPartitionInitialOffset[] topicPartitions = containerProperties.getTopicPartitions();
 55             if (topicPartitions != null//校验并发数>分区数，报错。
 56                     && this.concurrency > topicPartitions.length) {
 57                 this.logger.warn("When specific partitions are provided, the concurrency must be less than or "
 58                         + "equal to the number of partitions; reduced from " + this.concurrency + " to "
 59                         + topicPartitions.length);
 60                 this.concurrency = topicPartitions.length;//并发数最大只能=分区数
 61             }
 62             setRunning(true);
 63             //遍历创建监听器容器
 64             for (int i = 0; i < this.concurrency; i++) {
 65                 KafkaMessageListenerContainer<K, V> container;
 66                 if (topicPartitions == null) {
 67                     container = new KafkaMessageListenerContainer<>(this.consumerFactory, containerProperties);
 68                 }
 69                 else {
 70                     container = new KafkaMessageListenerContainer<>(this.consumerFactory, containerProperties,
 71                             partitionSubset(containerProperties, i));
 72                 }
 73                 if (getBeanName() != null) {
 74                     container.setBeanName(getBeanName() + "-" + i);
 75                 }
 76                 if (getApplicationEventPublisher() != null) {
 77                     container.setApplicationEventPublisher(getApplicationEventPublisher());
 78                 }
 79                 container.setClientIdSuffix("-" + i);
 80                 container.start();//核心方法，启动容器
 81                 this.containers.add(container);
 82             }
 83         }
 84     }146 ...省略
147 }

继续追踪，调用AbstractMessageListenerContainer的doStart(),值得注意的是start()和stop方法加了同一把锁，用于锁住生命周期。

 1 private final Object lifecycleMonitor = new Object();
 2 
 3 @Override
 4     public final void start() {
 5         synchronized (this.lifecycleMonitor) {
 6             Assert.isTrue(
 7                     this.containerProperties.getMessageListener() instanceof KafkaDataListener,
 8                     "A " + KafkaDataListener.class.getName() + " implementation must be provided");
 9             doStart();
10         }
11     }
12 
13     protected abstract void doStart();

最终调用的是KafkaMessageListenerContainer的doStart()

 1 @Override
 2     protected void doStart() {
 3         if (isRunning()) {
 4             return;
 5         }
 6         ContainerProperties containerProperties = getContainerProperties();
 7 
 8         if (!this.consumerFactory.isAutoCommit()) {
 9             AckMode ackMode = containerProperties.getAckMode();
10             if (ackMode.equals(AckMode.COUNT) || ackMode.equals(AckMode.COUNT_TIME)) {
11                 Assert.state(containerProperties.getAckCount() > 0, "'ackCount' must be > 0");
12             }
13             if ((ackMode.equals(AckMode.TIME) || ackMode.equals(AckMode.COUNT_TIME))
14                     && containerProperties.getAckTime() == 0) {
15                 containerProperties.setAckTime(5000);
16             }
17         }
18 
19         Object messageListener = containerProperties.getMessageListener();
20         Assert.state(messageListener != null, "A MessageListener is required");
21         if (messageListener instanceof GenericAcknowledgingMessageListener) {
22             this.acknowledgingMessageListener = (GenericAcknowledgingMessageListener<?>) messageListener;
23         }
24         else if (messageListener instanceof GenericMessageListener) {
25             this.listener = (GenericMessageListener<?>) messageListener;
26         }
27         else {
28             throw new IllegalStateException("messageListener must be 'MessageListener' "
29                     + "or 'AcknowledgingMessageListener', not " + messageListener.getClass().getName());
30         }
31         if (containerProperties.getConsumerTaskExecutor() == null) {
32             SimpleAsyncTaskExecutor consumerExecutor = new SimpleAsyncTaskExecutor(
33                     (getBeanName() == null ? "" : getBeanName()) + "-C-");
34             containerProperties.setConsumerTaskExecutor(consumerExecutor);
35         }
36         if (containerProperties.getListenerTaskExecutor() == null) {
37             SimpleAsyncTaskExecutor listenerExecutor = new SimpleAsyncTaskExecutor(
38                     (getBeanName() == null ? "" : getBeanName()) + "-L-");
39             containerProperties.setListenerTaskExecutor(listenerExecutor);
40         }//1.构建 监听消费者
41         this.listenerConsumer = new ListenerConsumer(this.listener, this.acknowledgingMessageListener);
42         setRunning(true);
　　　　　　//2.异步提交 监听消费者任务，返回Future并赋值。
43         this.listenerConsumerFuture = containerProperties
44                 .getConsumerTaskExecutor()
45                 .submitListenable(this.listenerConsumer);
46     }

doStart主要包含2个操作：构建内部类ListenerConsumer和提交监听消费者任务，返回Future并赋值。

1.构建内部类ListenerConsumer

ListenerConsumer类图如下：

ListenerConsumer构造函数源码如下：

 1 @SuppressWarnings("unchecked")
 2         ListenerConsumer(GenericMessageListener<?> listener, GenericAcknowledgingMessageListener<?> ackListener) {
 3             Assert.state(!this.isAnyManualAck || !this.autoCommit,
 4                     "Consumer cannot be configured for auto commit for ackMode " + this.containerProperties.getAckMode());
 5             @SuppressWarnings("deprecation")
 6             final Consumer<K, V> consumer =
 7                     KafkaMessageListenerContainer.this.consumerFactory instanceof
 8                                     org.springframework.kafka.core.ClientIdSuffixAware
 9                             ? ((org.springframework.kafka.core.ClientIdSuffixAware<K, V>) KafkaMessageListenerContainer
10                                     .this.consumerFactory)
11                                         .createConsumer(KafkaMessageListenerContainer.this.clientIdSuffix)
12                             : KafkaMessageListenerContainer.this.consumerFactory.createConsumer();
13 
14             this.theListener = listener == null ? ackListener : listener;
15             ConsumerRebalanceListener rebalanceListener = createRebalanceListener(consumer);
16 
17             if (KafkaMessageListenerContainer.this.topicPartitions == null) {
18                 if (this.containerProperties.getTopicPattern() != null) {
19                     consumer.subscribe(this.containerProperties.getTopicPattern(), rebalanceListener);
20                 }
21                 else {
22                     consumer.subscribe(Arrays.asList(this.containerProperties.getTopics()), rebalanceListener);
23                 }
24             }
25             else {
26                 List<TopicPartitionInitialOffset> topicPartitions =
27                         Arrays.asList(KafkaMessageListenerContainer.this.topicPartitions);
28                 this.definedPartitions = new HashMap<>(topicPartitions.size());
29                 for (TopicPartitionInitialOffset topicPartition : topicPartitions) {
30                     this.definedPartitions.put(topicPartition.topicPartition(),
31                             new OffsetMetadata(topicPartition.initialOffset(), topicPartition.isRelativeToCurrent()));
32                 }
33                 consumer.assign(new ArrayList<>(this.definedPartitions.keySet()));
34             }
35             this.consumer = consumer;
36             GenericErrorHandler<?> errHandler = this.containerProperties.getGenericErrorHandler();
37             this.genericListener = listener; 
               //1.
               if (this.theListener instanceof BatchAcknowledgingMessageListener) {
38                 this.listener = null;
39                 this.batchListener = null;
40                 this.acknowledgingMessageListener = null;
41                 this.batchAcknowledgingMessageListener = (BatchAcknowledgingMessageListener<K, V>) this.theListener;
42                 this.isBatchListener = true;
43             }//2.
44             else if (this.theListener instanceof AcknowledgingMessageListener) {
45                 this.listener = null;
46                 this.acknowledgingMessageListener = (AcknowledgingMessageListener<K, V>) this.theListener;
47                 this.batchListener = null;
48                 this.batchAcknowledgingMessageListener = null;
49                 this.isBatchListener = false;
50             }//3.
51             else if (this.theListener instanceof BatchMessageListener) {
52                 this.listener = null;
53                 this.batchListener = (BatchMessageListener<K, V>) this.theListener;
54                 this.acknowledgingMessageListener = null;
55                 this.batchAcknowledgingMessageListener = null;
56                 this.isBatchListener = true;
57             }//4.
58             else if (this.theListener instanceof MessageListener) {
59                 this.listener = (MessageListener<K, V>) this.theListener;
60                 this.batchListener = null;
61                 this.acknowledgingMessageListener = null;
62                 this.batchAcknowledgingMessageListener = null;
63                 this.isBatchListener = false;
64             }
65             else {
66                 throw new IllegalArgumentException("Listener must be one of 'MessageListener', "
67                         + "'BatchMessageListener', 'AcknowledgingMessageListener', "
68                         + "'BatchAcknowledgingMessageListener', not " + this.theListener.getClass().getName());
69             }
70             if (this.isBatchListener) {
71                 validateErrorHandler(true);
72                 this.errorHandler = new LoggingErrorHandler();
73                 this.batchErrorHandler = errHandler == null ? new BatchLoggingErrorHandler()
74                         : (BatchErrorHandler) errHandler;
75             }
76             else {
77                 validateErrorHandler(false);
78                 this.errorHandler = errHandler == null ? new LoggingErrorHandler() : (ErrorHandler) errHandler;
79                 this.batchErrorHandler = new BatchLoggingErrorHandler();
80             }
81             Assert.state(!this.isBatchListener || !this.isRecordAck, "Cannot use AckMode.RECORD with a batch listener");
82         }

1.定义消费者订阅topic或者指定分区

2.设置监听器，支持4种：

　　1）BatchAcknowledgingMessageListener批量需确认消息监听器

　　2）AcknowledgingMessageListener需确认消息监听器

　　3）BatchMessageListener批量消息监听器

　　4）MessageListener消息监听器（用的最多，一次消费一条）

2.提交监听消费者任务（ListenerConsumer），返回Future并赋值。

这里我们看一下任务Runnable接口的run方法，分两种情况

1.如果自定义了分区,没必要再平衡分配分区了，直接回调

2.未指定分区，进入自旋消费

 1 @Override
 2         public void run() {
 3             if (this.genericListener instanceof ConsumerSeekAware) {
 4                 ((ConsumerSeekAware) this.genericListener).registerSeekCallback(this);
 5             }
 6             this.count = 0;
 7             this.last = System.currentTimeMillis();
 8             if (isRunning() && this.definedPartitions != null) {// 1.如果运行中且自定义了分区,没必要再平衡分配分区了，直接回调
 9                 initPartitionsIfNeeded();// 有需要就初始化分区
10                 // 回调
13                 if (!this.autoCommit) {
14                     startInvoker();
15                 }
16             }
17             long lastReceive = System.currentTimeMillis();
18             long lastAlertAt = lastReceive;
19             while (isRunning()) {//2.未指定分区，进入自旋消费
20                 try {
21                     if (!this.autoCommit) {
22                         processCommits();// 如果手动提交，处理提交
23                     }
24                     processSeeks();// 重新定位偏移量，下一次消费时使用
25                     if (this.logger.isTraceEnabled()) {
26                         this.logger.trace("Polling (paused=" + this.paused + ")...");
27                     }// 1）拉取消费记录
28                     ConsumerRecords<K, V> records = this.consumer.poll(this.containerProperties.getPollTimeout());
29                     if (records != null && this.logger.isDebugEnabled()) {
30                         this.logger.debug("Received: " + records.count() + " records");
31                     }
32                     if (records != null && records.count() > 0) {
33                         if (this.containerProperties.getIdleEventInterval() != null) {
34                             lastReceive = System.currentTimeMillis();
35                         }// 2）如果设置了自动提交，直接在当前线程执行
39                         if (this.autoCommit) {
40                             invokeListener(records);
41                         }
42                         else {// 3）否则发送消息进缓存队列
43                             if (sendToListener(records)) {
44                                 if (this.assignedPartitions != null) {
45                                     // avoid group management rebalance due to a slow
46                                     // consumer
47                                     this.consumer.pause(this.assignedPartitions);
48                                     this.paused = true;
49                                     this.unsent = records;
50                                 }
51                             }
52                         }
53                     }
54                     else {
55                         if (this.containerProperties.getIdleEventInterval() != null) {
56                             long now = System.currentTimeMillis();
57                             if (now > lastReceive + this.containerProperties.getIdleEventInterval()
58                                     && now > lastAlertAt + this.containerProperties.getIdleEventInterval()) {
59                                 publishIdleContainerEvent(now - lastReceive);
60                                 lastAlertAt = now;
61                                 if (this.genericListener instanceof ConsumerSeekAware) {
62                                     seekPartitions(getAssignedPartitions(), true);
63                                 }
64                             }
65                         }
66                     }
67                     this.unsent = checkPause(this.unsent);
68                 }
69                 catch (WakeupException e) {
70                     this.unsent = checkPause(this.unsent);
71                 }
72                 catch (Exception e) {
73                     if (this.containerProperties.getGenericErrorHandler() != null) {
74                         this.containerProperties.getGenericErrorHandler().handle(e, null);
75                     }
76                     else {
77                         this.logger.error("Container exception", e);
78                     }
79                 }
80             }
81             if (this.listenerInvokerFuture != null) {
82                 stopInvoker();
83                 commitManualAcks();
84             }
85             try {
86                 this.consumer.unsubscribe();
87             }
88             catch (WakeupException e) {
89                 // No-op. Continue process
90             }
91             this.consumer.close();
92             if (this.logger.isInfoEnabled()) {
93                 this.logger.info("Consumer stopped");
94             }
95         }

1.如果用户自定义了分区且非自动提交，那么开启异步线程执行ListenerInvoker任务，源码如下：

1 private void startInvoker() {
2             ListenerConsumer.this.invoker = new ListenerInvoker();
3             ListenerConsumer.this.listenerInvokerFuture = this.containerProperties.getListenerTaskExecutor()
4                     .submit(ListenerConsumer.this.invoker);
5         }

执行ListenerInvoker的run方法，实际上就执行一遍，因为CountDownLatch初始化为1

 1 private final class ListenerInvoker implements SchedulingAwareRunnable {
 2 
 3             private final CountDownLatch exitLatch = new CountDownLatch(1);
 4 
 5             private volatile boolean active = true;
 6 
 7             private volatile Thread executingThread;
 8 
 9             ListenerInvoker() {
10                 super();
11             }
12 
13             @Override
14             public void run() {
15                 Assert.isTrue(this.active, "This instance is not active anymore");
16                 if (ListenerConsumer.this.theListener instanceof ConsumerSeekAware) {
17                     ((ConsumerSeekAware) ListenerConsumer.this.theListener).registerSeekCallback(ListenerConsumer.this);
18                 }
19                 try {
20                     this.executingThread = Thread.currentThread();
21                     while (this.active) {
22                         try {// 从阻塞队列LinkedBlockingQueue recordsToProcess中拉取 待消费记录
23                             ConsumerRecords<K, V> records = ListenerConsumer.this.recordsToProcess.poll(1,
24                                     TimeUnit.SECONDS);
25                             if (this.active) {
26                                 if (records != null) {
27                                     invokeListener(records);// 消费
28                                 }
29                                 else {
30                                     if (ListenerConsumer.this.logger.isTraceEnabled()) {
31                                         ListenerConsumer.this.logger.trace("No records to process");
32                                     }
33                                 }
34                             }
35                         }
36                         catch (InterruptedException e) {
37                             if (!this.active) {
38                                 Thread.currentThread().interrupt();
39                             }
40                             else {
41                                 ListenerConsumer.this.logger.debug("Interrupt ignored");
42                             }
43                         }
44                     }
45                 }
46                 finally {
47                     this.active = false;
48                     this.exitLatch.countDown();
49                 }
50             }
51 
52             @Override
53             public boolean isLongLived() {
54                 return true;
55             }
581         }

1 private void invokeListener(final ConsumerRecords<K, V> records) {
2             if (this.isBatchListener) {
3                 invokeBatchListener(records);
4             }
5             else {
6                 invokeRecordListener(records);
7             }
8         }

如上图，从阻塞队列中取得待消费记录，用迭代器iterator消费，根据自定义消费类型，用不同listener来执行onMessage方法（用户自定义MessageListener接口的onMessage方法，实现用户自己的消费业务逻辑）

 1 private void invokeRecordListener(final ConsumerRecords<K, V> records) {
 2             Iterator<ConsumerRecord<K, V>> iterator = records.iterator();
 3             while (iterator.hasNext() && (this.autoCommit || (this.invoker != null && this.invoker.active))) {
 4                 final ConsumerRecord<K, V> record = iterator.next();
 5                 if (this.logger.isTraceEnabled()) {
 6                     this.logger.trace("Processing " + record);
 7                 }
 8                 try {
 9                     if (this.acknowledgingMessageListener != null) {
10                         this.acknowledgingMessageListener.onMessage(record,// 终极核心方法，用户自定义的MessageListener接口的onMessage方法
11                                 this.isAnyManualAck
12                                         ? new ConsumerAcknowledgment(record, this.isManualImmediateAck)
13                                         : null);
14                     }
15                     else {
16                         this.listener.onMessage(record);// 终极核心方法，用户自定义的MessageListener接口的onMessage方法
17                     }
18                     if (!this.isAnyManualAck && !this.autoCommit) {
19                         this.acks.add(record);
20                     }
21                 }
22                 catch (Exception e) {
23                     if (this.containerProperties.isAckOnError() && !this.autoCommit) {
24                         this.acks.add(record);
25                     }
26                     try {
27                         this.errorHandler.handle(e, record);
28                     }
29                     catch (Exception ee) {
30                         this.logger.error("Error handler threw an exception", ee);
31                     }
32                     catch (Error er) { //NOSONAR
33                         this.logger.error("Error handler threw an error", er);
34                         throw er;
35                     }
36                 }
37             }
38         }

2.未指定分区，进入自旋

// 1）拉取消费记录
ConsumerRecords<K, V> records = this.consumer.poll(this.containerProperties.getPollTimeout());

 2）如果设置了自动提交，直接在当前线程执行
invokeListener(records);

// 3）否则发送消息进缓存队列
sendToListener(records)

1）在每个轮询中，消费者将尝试使用最后一个被使用的偏移量作为起始偏移量，并按顺序提取。最后一个被消费的偏移量可以通过 seek(TopicPartition,long)或自动设置为最后一个被订阅的分区列表的偏移量获得。

 1 @Override
 2     public ConsumerRecords<K, V> poll(long timeout) {
 3         acquire();
 4         try {
 5             if (timeout < 0)
 6                 throw new IllegalArgumentException("Timeout must not be negative");
 7 
 8             if (this.subscriptions.hasNoSubscriptionOrUserAssignment())
 9                 throw new IllegalStateException("Consumer is not subscribed to any topics or assigned any partitions");
10 
11             // poll for new data until the timeout expires
12             long start = time.milliseconds();
13             long remaining = timeout;
14             do {
15                 Map<TopicPartition, List<ConsumerRecord<K, V>>> records = pollOnce(remaining);
16                 if (!records.isEmpty()) {
23                     fetcher.sendFetches();// 在返回所获取的记录之前，我们可以发送下一轮的fetches并避免阻塞等待它们的响应，以便在用户处理获取的记录时进行流水线操作。
24                     client.pollNoWakeup();//由于已经更新了所使用的位置，所以我们不允许在返回所获取的记录之前触发wakeups或任何其他错误。
25 
26                     if (this.interceptors == null)
27                         return new ConsumerRecords<>(records);
28                     else// 如果存在消费者拦截器执行拦截
29                         return this.interceptors.onConsume(new ConsumerRecords<>(records));
30                 }
31 
32                 long elapsed = time.milliseconds() - start;
33                 remaining = timeout - elapsed;
34             } while (remaining > 0);
35 
36             return ConsumerRecords.empty();
37         } finally {
38             release();
39         }
40     }

pollOnce：

 1 private Map<TopicPartition, List<ConsumerRecord<K, V>>> pollOnce(long timeout) {
 2         coordinator.poll(time.milliseconds());
 3 
 4         // 遍历所有的TopicPartition，如果有未知偏移量（分区的），那么更新。涉及coordinator刷新已提交分区偏移量+fetcher更新获取位置
 6         if (!subscriptions.hasAllFetchPositions())
 7             updateFetchPositions(this.subscriptions.missingFetchPositions());
 8 
 9         // 返回已获取到的记录
10         Map<TopicPartition, List<ConsumerRecord<K, V>>> records = fetcher.fetchedRecords();
11         if (!records.isEmpty())
12             return records;
13 
14         // 发送fetch请求
15         fetcher.sendFetches();
16 
17         long now = time.milliseconds();
18         long pollTimeout = Math.min(coordinator.timeToNextPoll(now), timeout);
19         // 执行IO，拉取数据
20         client.poll(pollTimeout, now, new PollCondition() {
21             @Override
22             public boolean shouldBlock() {
23                 // since a fetch might be completed by the background thread, we need this poll condition
24                 // to ensure that we do not block unnecessarily in poll()
25                 return !fetcher.hasCompletedFetches();
26             }
27         });
31         if (coordinator.needRejoin())
32             return Collections.emptyMap();
33 
34         return fetcher.fetchedRecords();
35     }

好吧，再往下涉及到通信IO层了，这里不再多说。将来补全了kafka通信协议相关文章后再加上飞机票。

2）invokeListener和分支1一样，最终调用的是用户自定义的MessageListener接口的onMessage方法，不再重复。

3) sendToListener,这里塞进缓存队列LinkedBlockingQueue<ConsumerRecords<K, V>> recordsToProcess,塞进队列后，何时再消费？ListenerInvoker的run方法执行了recordsToProcess.poll进行了消费，

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只会一点java

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