今天研究rocketmq的时候，发现ScheduledExecutorService这个类scheduleAtFixedRate方法可以让main方法一直运行

代码如下：

package com.yuanqiao;

import org.apache.rocketmq.client.impl.factory.MQClientInstance;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;

public class ThreadTest  {

    private final ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(new ThreadFactory() {
        @Override
        public Thread newThread(Runnable r) {
            return new Thread(r, "MQClientFactoryScheduledThread");
        }
    });


    public static void main(String[] args) {
        new ThreadTest().scheduledExecutorService.scheduleAtFixedRate(new Runnable() {

            @Override
            public void run() {
                System.out.println("每隔几秒打印一次");
            }
        }, 1000 * 10, 1000 * 60 * 2, TimeUnit.MILLISECONDS);
    }


}

　　

一开始我研究的rocketmq的代码如下：

package com.yuanqiao;

import org.apache.rocketmq.client.consumer.DefaultMQPushConsumer;
import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyStatus;
import org.apache.rocketmq.client.consumer.listener.MessageListenerConcurrently;
import org.apache.rocketmq.client.exception.MQClientException;
import org.apache.rocketmq.common.consumer.ConsumeFromWhere;
import org.apache.rocketmq.common.message.MessageExt;

import java.util.List;

public class RocketMQConsumer {


    public static void main(String[] args) throws InterruptedException, MQClientException {

        //声明并初始化一个consumer
        //需要一个consumer group名字作为构造方法的参数，这里为consumer1
        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("consumer1");

        //同样也要设置NameServer地址
        consumer.setNamesrvAddr("10.1.54.121:9876;10.1.54.122:9876");

        //这里设置的是一个consumer的消费策略
        //CONSUME_FROM_LAST_OFFSET 默认策略，从该队列最尾开始消费，即跳过历史消息
        //CONSUME_FROM_FIRST_OFFSET 从队列最开始开始消费，即历史消息（还储存在broker的）全部消费一遍
        //CONSUME_FROM_TIMESTAMP 从某个时间点开始消费，和setConsumeTimestamp()配合使用，默认是半个小时以前
        consumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_FIRST_OFFSET);

        //设置consumer所订阅的Topic和Tag，*代表全部的Tag
        consumer.subscribe("TopicTest", "*");

        //设置一个Listener，主要进行消息的逻辑处理
        consumer.registerMessageListener(new MessageListenerConcurrently() {

            @Override
            public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs,
                                                            ConsumeConcurrentlyContext context) {

                System.out.println(Thread.currentThread().getName() + " Receive New Messages: " + msgs);

                //返回消费状态
                //CONSUME_SUCCESS 消费成功
                //RECONSUME_LATER 消费失败，需要稍后重新消费
                return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
            }
        });

        //调用start()方法启动consumer
        consumer.start();

        System.out.println("Consumer Started.");
    }
}

　　

由于我没有安装rocketmq中间件，知识maven引入了rocketmq客户端，所以报错了，但是我发现main方法居然没有执行退出，于是调试了一下。

        <dependency>
            <groupId>org.apache.rocketmq</groupId>
            <artifactId>rocketmq-client</artifactId>
            <version>4.7.1</version>
        </dependency>

　　

报错但是程序没有结束的截图如下：

报错信息如下：

Exception in thread "main" java.lang.IllegalStateException: org.apache.rocketmq.remoting.exception.RemotingConnectException: connect to [10.1.54.122:9876, 10.1.54.121:9876] failed
	at org.apache.rocketmq.client.impl.factory.MQClientInstance.updateTopicRouteInfoFromNameServer(MQClientInstance.java:679)
	at org.apache.rocketmq.client.impl.factory.MQClientInstance.updateTopicRouteInfoFromNameServer(MQClientInstance.java:509)
	at org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl.updateTopicSubscribeInfoWhenSubscriptionChanged(DefaultMQPushConsumerImpl.java:872)
	at org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl.start(DefaultMQPushConsumerImpl.java:653)
	at org.apache.rocketmq.client.consumer.DefaultMQPushConsumer.start(DefaultMQPushConsumer.java:698)
	at com.yuanqiao.RocketMQConsumer.main(RocketMQConsumer.java:51)
Caused by: org.apache.rocketmq.remoting.exception.RemotingConnectException: connect to [10.1.54.122:9876, 10.1.54.121:9876] failed
	at org.apache.rocketmq.remoting.netty.NettyRemotingClient.getAndCreateNameserverChannel(NettyRemotingClient.java:445)
	at org.apache.rocketmq.remoting.netty.NettyRemotingClient.getAndCreateChannel(NettyRemotingClient.java:400)
	at org.apache.rocketmq.remoting.netty.NettyRemotingClient.invokeSync(NettyRemotingClient.java:369)
	at org.apache.rocketmq.client.impl.MQClientAPIImpl.getTopicRouteInfoFromNameServer(MQClientAPIImpl.java:1363)
	at org.apache.rocketmq.client.impl.MQClientAPIImpl.getTopicRouteInfoFromNameServer(MQClientAPIImpl.java:1353)
	at org.apache.rocketmq.client.impl.factory.MQClientInstance.updateTopicRouteInfoFromNameServer(MQClientInstance.java:622)
	... 5 more

　

跟踪代码，发现报错前，有启动定时任务的其他代码存在：

org.apache.rocketmq.client.impl.factory.MQClientInstance#start

　org.apache.rocketmq.client.impl.factory.MQClientInstance#startScheduledTask