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说明

rocketmq-spring的consumer的相关属性配置有两种方式：

1. 在配置文件中进行配置
2. 类上使用@RocketMQMessageListener注解配置相关属性

关于注解中的属性可以查看：org.apache.rocketmq.spring.annotation.RocketMQMessageListener，而在文件中可以配置的属性只有如下几个（并不遵守spring boot自动配置规范，所以在idea中不会有相关提示）

说明如下：

rocketmq.consumer.customized-trace-topic

rocketmq.access-channe

如果想要设置最大重试次数等一些相关初始化参数配置，很明显是不支持的。

同时，看一下构造consumer的源码，可以看到只配置了固定的几个属性：

    private void initRocketMQPushConsumer() throws MQClientException {

        RPCHook rpcHook = RocketMQUtil.getRPCHookByAkSk(applicationContext.getEnvironment(),
            this.rocketMQMessageListener.accessKey(), this.rocketMQMessageListener.secretKey());
        boolean enableMsgTrace = rocketMQMessageListener.enableMsgTrace();
        if (Objects.nonNull(rpcHook)) {
            consumer = new DefaultMQPushConsumer(consumerGroup, rpcHook, new AllocateMessageQueueAveragely(),
                enableMsgTrace, this.applicationContext.getEnvironment().
                resolveRequiredPlaceholders(this.rocketMQMessageListener.customizedTraceTopic()));
            consumer.setVipChannelEnabled(false);
            consumer.setInstanceName(RocketMQUtil.getInstanceName(rpcHook, consumerGroup));
        } else {
            log.debug("Access-key or secret-key not configure in " + this + ".");
            consumer = new DefaultMQPushConsumer(consumerGroup, enableMsgTrace,
                this.applicationContext.getEnvironment().
                    resolveRequiredPlaceholders(this.rocketMQMessageListener.customizedTraceTopic()));
        }

        String customizedNameServer = this.applicationContext.getEnvironment().resolveRequiredPlaceholders(this.rocketMQMessageListener.nameServer());
        if (customizedNameServer != null) {
            consumer.setNamesrvAddr(customizedNameServer);
        } else {
            consumer.setNamesrvAddr(nameServer);
        }
        if (accessChannel != null) {
            consumer.setAccessChannel(accessChannel);
        }
        consumer.setConsumeThreadMax(consumeThreadMax);
        if (consumeThreadMax < consumer.getConsumeThreadMin()) {
            consumer.setConsumeThreadMin(consumeThreadMax);
        }
        consumer.setConsumeTimeout(consumeTimeout);

        switch (messageModel) {
            case BROADCASTING:
                consumer.setMessageModel(org.apache.rocketmq.common.protocol.heartbeat.MessageModel.BROADCASTING);
                break;
            case CLUSTERING:
                consumer.setMessageModel(org.apache.rocketmq.common.protocol.heartbeat.MessageModel.CLUSTERING);
                break;
            default:
                throw new IllegalArgumentException("Property 'messageModel' was wrong.");
        }

        switch (selectorType) {
            case TAG:
                consumer.subscribe(topic, selectorExpression);
                break;
            case SQL92:
                consumer.subscribe(topic, MessageSelector.bySql(selectorExpression));
                break;
            default:
                throw new IllegalArgumentException("Property 'selectorType' was wrong.");
        }

        switch (consumeMode) {
            case ORDERLY:
                consumer.setMessageListener(new DefaultMessageListenerOrderly());
                break;
            case CONCURRENTLY:
                consumer.setMessageListener(new DefaultMessageListenerConcurrently());
                break;
            default:
                throw new IllegalArgumentException("Property 'consumeMode' was wrong.");
        }

        if (rocketMQListener instanceof RocketMQPushConsumerLifecycleListener) {
            ((RocketMQPushConsumerLifecycleListener) rocketMQListener).prepareStart(consumer);
        } else if (rocketMQReplyListener instanceof RocketMQPushConsumerLifecycleListener) {
            ((RocketMQPushConsumerLifecycleListener) rocketMQReplyListener).prepareStart(consumer);
        }

    }

但是看代码的最后几行，rocketMQListener如果实现了RocketMQPushConsumerLifecycleListener接口，则会调用RocketMQPushConsumerLifecycleListener的prepareStart(consumer)方法，很明显，可以在这里设置consuemr的参数。

说明：rocketMQListener就是类上带有RocketMQMessageListener的bean。

解决方案

    @RocketMQMessageListener(topic = "test_topic", consumerGroup = "test_topic_consumer", selectorExpression = "*")
    class StringConsumer implements RocketMQListener<String>, RocketMQPushConsumerLifecycleListener {

        @Override
        public void onMessage(String message) {
            LOGGER.info("receive message: {}", message);
        }

        @Override public void prepareStart(DefaultMQPushConsumer consumer) {
            // 设置最大重试次数
            consumer.setMaxReconsumeTimes(5);
            // 如下，设置其它consumer相关属性
            consumer.setPullBatchSize(16);
        }
    }

末语

我是在翻源码的才想到这个解决方案，我想既然提供有这个接口进行自定义配置，官方文档应该会有示例说明，然后翻了下github，是有类似的使用方式的，源码上还有其它示例，如果有其它问题，建议还是先看官方示例是否提供了相关解决方案。github地址：https://github.com/apache/rocketmq-spring/tree/master/rocketmq-spring-boot-samples/rocketmq-consume-demo/src/main/java/org/apache/rocketmq/samples/springboot/consumer

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