最近做RabbitMQ故障演练发现RabbitMQ服务器停止后，基于springboot的消费端不可以自动的恢复，队列的消费者消失，消息一直积压到队列中，这种情况肯定是不可接收的；通过研究源代码找到了解决方案。
一、添加自动恢复配置automaticRecovery
java
CachingConnectionFactory factory = new CachingConnectionFactory(connectionFactory);
cachingConnectionFactoryConfigurer.configure(factory);
//设置TCP连接超时时间，默认：60000ms
factory.getRabbitConnectionFactory().setConnectionTimeout(properties.getConnectionTimeout());
//启用或禁用连接自动恢复，默认：false
factory.getRabbitConnectionFactory().setAutomaticRecoveryEnabled(properties.isAutomaticRecovery());
//设置连接恢复时间间隔，默认：5000ms
factory.getRabbitConnectionFactory().setNetworkRecoveryInterval(properties.getNetworkRecoveryInterval());
//启用或禁用拓扑恢复，默认：true【拓扑恢复功能可以帮助消费者重新声明之前定义的队列、交换机和绑定等拓扑结构】
factory.getRabbitConnectionFactory().setTopologyRecoveryEnabled(properties.isTopologyRecovery());
//替换默认异常处理DefaultExceptionHandler
factory.getRabbitConnectionFactory().setExceptionHandler(new DefaultMqExceptionHandler());
//添加连接监听器
factory.addConnectionListener(new DefaultMqConnectionListener(factory));通过上述配置如果RabbitMQ服务器发生故障，则会自动重启恢复连接及队列的消费者，如果恢复失败则会间隔5000ms再次重试；在这里提一个问题，如果服务重试一直失败，重试的上限是多少？带着这个问题我们分析下源码。
二、RabbitMQ客户端实现连接的自动恢复功能
AutorecoveringConnection#beginAutomaticRecovery是在 RabbitMQ 客户端库层面实现的连接的自动恢复功能。当 RabbitMQ 连接出现故障时，它会尝试重新建立连接，以确保消息传递的可靠性。
java
private synchronized void beginAutomaticRecovery() throws InterruptedException {
//获取故障恢复连接的间隔时间，实际是设置的：networkRecoveryInterval
final long delay = this.params.getRecoveryDelayHandler().getDelay(0);
if (delay > 0) {
//等待指定的间隔时间
this.wait(delay);
}
//调用恢复通知监听器
this.notifyRecoveryListenersStarted();
//获取恢复建立的连接对象
final RecoveryAwareAMQConnection newConn = this.recoverConnection();
//如果为null则直接返回
if (newConn == null) {
return;
}
//连接已经恢复建立，恢复监听器、channel等资源
LOGGER.debug("Connection {} has recovered", newConn);
this.addAutomaticRecoveryListener(newConn);
this.recoverShutdownListeners(newConn);
this.recoverBlockedListeners(newConn);
this.recoverChannels(newConn);
// don't assign new delegate connection until channel recovery is complete
this.delegate = newConn;
//判断是否恢复拓扑结构，如果开启则开启拓扑结构恢复
if (this.params.isTopologyRecoveryEnabled()) {
notifyTopologyRecoveryListenersStarted();
recoverTopology(params.getTopologyRecoveryExecutor());
}
this.notifyRecoveryListenersComplete();
}addAutomaticRecoveryListener自动恢复监听器
java
private void addAutomaticRecoveryListener(final RecoveryAwareAMQConnection newConn) {
final AutorecoveringConnection c = this;
// this listener will run after shutdown listeners,
// see https://github.com/rabbitmq/rabbitmq-java-client/issues/135
RecoveryCanBeginListener starter = cause -> {
try {
if (shouldTriggerConnectionRecovery(cause)) {
//开始自动回复
c.beginAutomaticRecovery();
}
} catch (Exception e) {
newConn.getExceptionHandler().handleConnectionRecoveryException(c, e);
}
};
synchronized (this) {
newConn.addRecoveryCanBeginListener(starter);
}
}init初始化
java
public void init() throws IOException, TimeoutException {
//建立连接，否则抛出异常
this.delegate = this.cf.newConnection();
//自动回复监听器
this.addAutomaticRecoveryListener(delegate);
}三、消费端实现消息的消费和处理
SimpleMessageListenerContainer.AsyncMessageProcessingConsumer#run是应用程序层面实现消息的消费和处理，它负责从RabbitMQ中接收消息并进行相应的逻辑处理：
java
@Override // NOSONAR - complexity - many catch blocks
public void run() { // NOSONAR - line count
...
try {
//消费端初始化方法
initialize();
//当消费端是活跃状态，或者队列非空，或者消费端未被关闭则进入主循环
while (isActive(this.consumer) || this.consumer.hasDelivery() || !this.consumer.cancelled()) {
mainLoop();
}
}
catch (InterruptedException e) {
...
}
}消费端initialize初始化方法：
java
private void initialize() throws Throwable { // NOSONAR
try {
redeclareElementsIfNecessary();
//启动消费端初始化
this.consumer.start();
this.start.countDown();
}
catch (QueuesNotAvailableException e) {
if (isMissingQueuesFatal()) {
throw e;
}
else {
this.start.countDown();
//消费端启动异常等待处理
handleStartupFailure(this.consumer.getBackOffExecution());
throw e;
}
}
catch (FatalListenerStartupException ex) {
if (isPossibleAuthenticationFailureFatal()) {
throw ex;
}
else {
Throwable possibleAuthException = ex.getCause().getCause();
if (!(possibleAuthException instanceof PossibleAuthenticationFailureException)) {
throw ex;
}
else {
this.start.countDown();
//消费端启动异常等待处理
handleStartupFailure(this.consumer.getBackOffExecution());
throw possibleAuthException;
}
}
}
catch (Throwable t) { //NOSONAR
this.start.countDown();
//消费端启动异常等待处理
handleStartupFailure(this.consumer.getBackOffExecution());
throw t;
}
if (getTransactionManager() != null) {
/*
* Register the consumer's channel so it will be used by the transaction manager
* if it's an instance of RabbitTransactionManager.
*/
ConsumerChannelRegistry.registerConsumerChannel(this.consumer.getChannel(), getConnectionFactory());
}
}消费端异常等待处理处理：
java
protected void handleStartupFailure(BackOffExecution backOffExecution) {
//获取等待时间间隔，参考FixedBackOff类实现
long recoveryInterval = backOffExecution.nextBackOff();
if (BackOffExecution.STOP == recoveryInterval) {
synchronized (this) {
if (isActive()) {
logger.warn("stopping container - restart recovery attempts exhausted");
stop();
}
}
return;
}
try {
if (logger.isDebugEnabled() && isActive()) {
logger.debug("Recovering consumer in " + recoveryInterval + " ms.");
}
//当前时间加上等待时间
long timeout = System.currentTimeMillis() + recoveryInterval;
//如果当前时间小于等待时间，则休眠200毫秒，再次尝试
while (isActive() && System.currentTimeMillis() < timeout) {
Thread.sleep(RECOVERY_LOOP_WAIT_TIME);
}
}
catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new IllegalStateException("Irrecoverable interruption on consumer restart", e);
}
}FixedBackOff回退等待时间类实现：
java
public class FixedBackOff implements BackOff {
// 默认恢复重试间隔
public static final long DEFAULT_INTERVAL = 5000L;
//最大重试次数，可以认为无限大
public static final long UNLIMITED_ATTEMPTS = Long.MAX_VALUE;
// 默认恢复重试间隔
private long interval = 5000L;
//最大重试次数，可以认为无限大
private long maxAttempts = Long.MAX_VALUE;
public FixedBackOff() {
}
public FixedBackOff(long interval, long maxAttempts) {
this.interval = interval;
this.maxAttempts = maxAttempts;
}
public void setInterval(long interval) {
this.interval = interval;
}
public long getInterval() {
return this.interval;
}
public void setMaxAttempts(long maxAttempts) {
this.maxAttempts = maxAttempts;
}
public long getMaxAttempts() {
return this.maxAttempts;
}
public BackOffExecution start() {
return new FixedBackOffExecution();
}
private class FixedBackOffExecution implements BackOffExecution {
private long currentAttempts;
private FixedBackOffExecution() {
this.currentAttempts = 0L;
}
//获取下一次尝试的时间间隔，可以认为一直都是5000ms
public long nextBackOff() {
++this.currentAttempts;
return this.currentAttempts <= FixedBackOff.this.getMaxAttempts() ? FixedBackOff.this.getInterval() : -1L;
}
public String toString() {
String attemptValue = FixedBackOff.this.maxAttempts == Long.MAX_VALUE ? "unlimited" : String.valueOf(FixedBackOff.this.maxAttempts);
return "FixedBackOff{interval=" + FixedBackOff.this.interval + ", currentAttempts=" + this.currentAttempts + ", maxAttempts=" + attemptValue + '}';
}
}
}总结：综上源码分析可知消费端故障恢复重试等待时间是5000ms,重试次数可以认为是无限制（Long最大值）
mainloop主循环逻辑：
java
private void mainLoop() throws Exception { // NOSONAR Exception
try {
if (SimpleMessageListenerContainer.this.stopNow.get()) {
this.consumer.forceCloseAndClearQueue();
return;
}
//接收客户端发送过来的消息，至少获取一条
boolean receivedOk = receiveAndExecute(this.consumer); // At least one message received
if (SimpleMessageListenerContainer.this.maxConcurrentConsumers != null) {
checkAdjust(receivedOk);
}
long idleEventInterval = getIdleEventInterval();
if (idleEventInterval > 0) {
if (receivedOk) {
updateLastReceive();
}
else {
long now = System.currentTimeMillis();
long lastAlertAt = SimpleMessageListenerContainer.this.lastNoMessageAlert.get();
long lastReceive = getLastReceive();
if (now > lastReceive + idleEventInterval
&& now > lastAlertAt + idleEventInterval
&& SimpleMessageListenerContainer.this.lastNoMessageAlert
.compareAndSet(lastAlertAt, now)) {
publishIdleContainerEvent(now - lastReceive);
}
}
}
}
catch (ListenerExecutionFailedException ex) {
// Continue to process, otherwise re-throw
if (ex.getCause() instanceof NoSuchMethodException) {
throw new FatalListenerExecutionException("Invalid listener", ex);
}
}
catch (AmqpRejectAndDontRequeueException rejectEx) {
/*
* These will normally be wrapped by an LEFE if thrown by the
* listener, but we will also honor it if thrown by an
* error handler.
*/
}
}receiveAndExecute接收和处理消息：
java
private boolean receiveAndExecute(final BlockingQueueConsumer consumer) throws Exception { // NOSONAR
PlatformTransactionManager transactionManager = getTransactionManager();
if (transactionManager != null) {
try {
if (this.transactionTemplate == null) {
this.transactionTemplate =
new TransactionTemplate(transactionManager, getTransactionAttribute());
}
return this.transactionTemplate
.execute(status -> { // NOSONAR null never returned
RabbitResourceHolder resourceHolder = ConnectionFactoryUtils.bindResourceToTransaction(
new RabbitResourceHolder(consumer.getChannel(), false),
getConnectionFactory(), true);
// unbound in ResourceHolderSynchronization.beforeCompletion()
try {
//接收处理消息
return doReceiveAndExecute(consumer);
}
catch (RuntimeException e1) {
prepareHolderForRollback(resourceHolder, e1);
throw e1;
}
catch (Exception e2) {
throw new WrappedTransactionException(e2);
}
});
}
catch (WrappedTransactionException e) { // NOSONAR exception flow control
throw (Exception) e.getCause();
}
}
//接收处理消息
return doReceiveAndExecute(consumer);
}调用具体的消息监听器消费消息：
java
private void doExecuteListener(Channel channel, Object data) {
if (data instanceof Message) {
Message message = (Message) data;
if (this.afterReceivePostProcessors != null) {
for (MessagePostProcessor processor : this.afterReceivePostProcessors) {
message = processor.postProcessMessage(message);
if (message == null) {
throw new ImmediateAcknowledgeAmqpException(
"Message Post Processor returned 'null', discarding message");
}
}
}
if (this.deBatchingEnabled && this.batchingStrategy.canDebatch(message.getMessageProperties())) {
this.batchingStrategy.deBatch(message, fragment -> invokeListener(channel, fragment));
}
else {
invokeListener(channel, message);
}
}
else {
invokeListener(channel, data);
}
}