rocketmq中ListenerContainerConfiguration的作用是什么，相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。

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ListenerContainerConfiguration

rocketmq-spring-boot-2.0.3-sources.jar!/org/apache/rocketmq/spring/autoconfigure/ListenerContainerConfiguration.java

@Configuration
public class ListenerContainerConfiguration implements ApplicationContextAware, SmartInitializingSingleton {
    private final static Logger log = LoggerFactory.getLogger(ListenerContainerConfiguration.class);

    private ConfigurableApplicationContext applicationContext;

    private AtomicLong counter = new AtomicLong(0);

    private StandardEnvironment environment;

    private RocketMQProperties rocketMQProperties;

    private ObjectMapper objectMapper;

    public ListenerContainerConfiguration(ObjectMapper rocketMQMessageObjectMapper,
        StandardEnvironment environment,
        RocketMQProperties rocketMQProperties) {
        this.objectMapper = rocketMQMessageObjectMapper;
        this.environment = environment;
        this.rocketMQProperties = rocketMQProperties;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = (ConfigurableApplicationContext) applicationContext;
    }

    @Override
    public void afterSingletonsInstantiated() {
        Map beans = this.applicationContext.getBeansWithAnnotation(RocketMQMessageListener.class);

        if (Objects.nonNull(beans)) {
            beans.forEach(this::registerContainer);
        }
    }

    private void registerContainer(String beanName, Object bean) {
        Class clazz = AopProxyUtils.ultimateTargetClass(bean);

        if (!RocketMQListener.class.isAssignableFrom(bean.getClass())) {
            throw new IllegalStateException(clazz + " is not instance of " + RocketMQListener.class.getName());
        }

        RocketMQMessageListener annotation = clazz.getAnnotation(RocketMQMessageListener.class);
        validate(annotation);

        String containerBeanName = String.format("%s_%s", DefaultRocketMQListenerContainer.class.getName(),
            counter.incrementAndGet());
        GenericApplicationContext genericApplicationContext = (GenericApplicationContext) applicationContext;

        genericApplicationContext.registerBean(containerBeanName, DefaultRocketMQListenerContainer.class,
            () -> createRocketMQListenerContainer(containerBeanName, bean, annotation));
        DefaultRocketMQListenerContainer container = genericApplicationContext.getBean(containerBeanName,
            DefaultRocketMQListenerContainer.class);
        if (!container.isRunning()) {
            try {
                container.start();
            } catch (Exception e) {
                log.error("Started container failed. {}", container, e);
                throw new RuntimeException(e);
            }
        }

        log.info("Register the listener to container, listenerBeanName:{}, containerBeanName:{}", beanName, containerBeanName);
    }

    private DefaultRocketMQListenerContainer createRocketMQListenerContainer(String name, Object bean, RocketMQMessageListener annotation) {
        DefaultRocketMQListenerContainer container = new DefaultRocketMQListenerContainer();

        String nameServer = environment.resolvePlaceholders(annotation.nameServer());
        nameServer = StringUtils.isEmpty(nameServer) ? rocketMQProperties.getNameServer() : nameServer;
        String accessChannel = environment.resolvePlaceholders(annotation.accessChannel());
        container.setNameServer(nameServer);
        if (!StringUtils.isEmpty(accessChannel)) {
            container.setAccessChannel(AccessChannel.valueOf(accessChannel));
        }
        container.setTopic(environment.resolvePlaceholders(annotation.topic()));
        container.setConsumerGroup(environment.resolvePlaceholders(annotation.consumerGroup()));
        container.setRocketMQMessageListener(annotation);
        container.setRocketMQListener((RocketMQListener) bean);
        container.setObjectMapper(objectMapper);
        container.setName(name);  // REVIEW ME, use the same clientId or multiple?

        return container;
    }

    private void validate(RocketMQMessageListener annotation) {
        if (annotation.consumeMode() == ConsumeMode.ORDERLY &&
            annotation.messageModel() == MessageModel.BROADCASTING) {
            throw new BeanDefinitionValidationException(
                "Bad annotation definition in @RocketMQMessageListener, messageModel BROADCASTING does not support ORDERLY message!");
        }
    }
}

• ListenerContainerConfiguration实现了ApplicationContextAware、SmartInitializingSingleton接口

• 其setApplicationContext方法保存了applicationContext；其afterSingletonsInstantiated方法会获取标注了RocketMQMessageListener注解的bean，然后挨个执行registerContainer

• registerContainer方法首先判断该bean是否是RocketMQListener的实现类，不是则抛出IllegalStateException；接着获取RocketMQMessageListener注解的信息，判断是否设置了不支持的属性；之后通过createRocketMQListenerContainer创建DefaultRocketMQListenerContainer并注册到applicationContext，然后对于没有running的container执行start方法

RocketMQMessageListener

rocketmq-spring-boot-2.0.3-sources.jar!/org/apache/rocketmq/spring/annotation/RocketMQMessageListener.java

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RocketMQMessageListener {

    String NAME_SERVER_PLACEHOLDER = "${rocketmq.name-server:}";
    String ACCESS_KEY_PLACEHOLDER = "${rocketmq.consumer.access-key:}";
    String SECRET_KEY_PLACEHOLDER = "${rocketmq.consumer.secret-key:}";
    String TRACE_TOPIC_PLACEHOLDER = "${rocketmq.consumer.customized-trace-topic:}";
    String ACCESS_CHANNEL_PLACEHOLDER = "${rocketmq.access-channel:}";

    /**
     * Consumers of the same role is required to have exactly same subscriptions and consumerGroup to correctly achieve
     * load balance. It's required and needs to be globally unique.
     *
     *
     * See here for further discussion.
     */
    String consumerGroup();

    /**
     * Topic name.
     */
    String topic();

    /**
     * Control how to selector message.
     *
     * @see SelectorType
     */
    SelectorType selectorType() default SelectorType.TAG;

    /**
     * Control which message can be select. Grammar please see {@link SelectorType#TAG} and {@link SelectorType#SQL92}
     */
    String selectorExpression() default "*";

    /**
     * Control consume mode, you can choice receive message concurrently or orderly.
     */
    ConsumeMode consumeMode() default ConsumeMode.CONCURRENTLY;

    /**
     * Control message mode, if you want all subscribers receive message all message, broadcasting is a good choice.
     */
    MessageModel messageModel() default MessageModel.CLUSTERING;

    /**
     * Max consumer thread number.
     */
    int consumeThreadMax() default 64;

    /**
     * Max consumer timeout, default 30s.
     */
    long consumeTimeout() default 30000L;

    /**
     * The property of "access-key".
     */
    String accessKey() default ACCESS_KEY_PLACEHOLDER;

    /**
     * The property of "secret-key".
     */
    String secretKey() default SECRET_KEY_PLACEHOLDER;

    /**
     * Switch flag instance for message trace.
     */
    boolean enableMsgTrace() default true;

    /**
     * The name value of message trace topic.If you don't config,you can use the default trace topic name.
     */
    String customizedTraceTopic() default TRACE_TOPIC_PLACEHOLDER;

    /**
     * The property of "name-server".
     */
    String nameServer() default NAME_SERVER_PLACEHOLDER;

    /**
     * The property of "access-channel".
     */
    String accessChannel() default ACCESS_CHANNEL_PLACEHOLDER;
}

• RocketMQMessageListener注解定义了consumerGroup、topic、selectorType、selectorExpression、consumeMode、messageModel、consumeThreadMax、consumeTimeout、accessKey、secretKey、enableMsgTrace、customizedTraceTopic、nameServer、accessChannel属性

小结

• ListenerContainerConfiguration实现了ApplicationContextAware、SmartInitializingSingleton接口

• 其setApplicationContext方法保存了applicationContext；其afterSingletonsInstantiated方法会获取标注了RocketMQMessageListener注解的bean，然后挨个执行registerContainer

• registerContainer方法首先判断该bean是否是RocketMQListener的实现类，不是则抛出IllegalStateException；接着获取RocketMQMessageListener注解的信息，判断是否设置了不支持的属性；之后通过createRocketMQListenerContainer创建DefaultRocketMQListenerContainer并注册到applicationContext，然后对于没有running的container执行start方法

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