系列目录
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
==============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，
来源：https://www.cnblogs.com/dennyzhangdd/p/7759876.html