RabbitMQ学习笔记五：RabbitMQ之优先级消息队列

RabbitMQ优先级队列注意点：

1、只有当消费者不足，不能及时进行消费的情况下，优先级队列才会生效

2、RabbitMQ3.5以后才支持优先级队列

代码在博客：RabbitMQ学习笔记三：Java实现RabbitMQ之与Spring集成 最后面有下载地址，只是做了少许改变，改变的代码如下：

消费者 spring-config.xml（还需要增加一个QueueListener监听器，代码就不复制到这里了，可以参考项目中的其他监听器）

<!-- ========================================RabbitMQ========================================= -->
    <!-- 连接工厂 -->
    <rabbit:connection-factory id="connectionFactory" host="localhost" publisher-confirms="true" virtual-host="/" username="guest" password="guest" />
    <!-- 监听器 -->
    <rabbit:listener-container connection-factory="connectionFactory">
        <!-- queues是队列名称，可填多个，用逗号隔开， method是ref指定的Bean调用Invoke方法执行的方法名称 -->
        <rabbit:listener queues="red" method="onMessage" ref="redQueueListener" />
        <rabbit:listener queues="blue" method="onMessage" ref="blueQueueListener" />
        <rabbit:listener queues="queue" method="queueList" ref="queueListener" />
    </rabbit:listener-container>
    <!-- 队列声明 -->
    <rabbit:queue name="red" durable="true" />
    <rabbit:queue name="blue" durable="true" />
    <rabbit:queue name="queue" durable="true" />
    <!-- 红色监听处理器 -->
    <bean id="redQueueListener" class="com.aitongyi.customer.RedQueueListener" />
    <!-- 颜色监听处理器 -->
    <bean id="blueQueueListener" class="com.aitongyi.customer.BlueQueueListener" />
    <!-- 优先级队列监听处理器 -->
    <bean id="queueListener" class="com.aitongyi.customer.QueueListener" />

生产者增加一个主方法：

public static void main(String[] args)
    {
        CachingConnectionFactory connectionFactory = new CachingConnectionFactory();
        connectionFactory.setAddresses("127.0.0.1:5672");
        connectionFactory.setUsername("guest");
        connectionFactory.setPassword("guest");
        connectionFactory.setVirtualHost("/");
        connectionFactory.setPublisherConfirms(true); // 必须要设置

        RabbitTemplate template = new RabbitTemplate(connectionFactory);

        for (final int i : priority)
        {
            template.convertAndSend("queue", (Object) ("queue" + i), new MessagePostProcessor() {

                @Override
                public Message postProcessMessage(Message arg0) throws AmqpException
                {
                    arg0.getMessageProperties().setPriority(i);
                    return arg0;
                }
            });
        }
    }

当然，还需要在客户端创建一个优先级队列：

注意，x-max-length = 9999，这个值最后不要写太大了，否则你电脑的内存会一直处于100%的使用状态（至于出现这种状况怎么解决，请点击：RabbitMQ学习笔记四：RabbitMQ命令（附疑难问题解决）），并且这个取值范围在0~255之间，超过了可能会出现问题，我测试了设置9999时，部分有问题，后面会把有问题的地方贴上来。

好了，所有的事情准备完毕了，我们先启动消费者，然后再运行主方法，此时的队列优先级设置为，private static final int[] priority = { 1, 5, 1, 2, 3, 4, 5, 5, 0, 3, 6, 10, 4, 100, 99, 98 };执行结果如下：

2017-05-16 09:51:48 399 [INFO] c.a.c.QueueListener - queueList Receved:queue1
2017-05-16 09:51:48 417 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:51:48 435 [INFO] c.a.c.QueueListener - queueList Receved:queue1
2017-05-16 09:51:48 493 [INFO] c.a.c.QueueListener - queueList Receved:queue2
2017-05-16 09:51:48 514 [INFO] c.a.c.QueueListener - queueList Receved:queue3
2017-05-16 09:51:48 596 [INFO] c.a.c.QueueListener - queueList Receved:queue4
2017-05-16 09:51:48 950 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:51:48 975 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:51:49 015 [INFO] c.a.c.QueueListener - queueList Receved:queue0
2017-05-16 09:51:49 039 [INFO] c.a.c.QueueListener - queueList Receved:queue3
2017-05-16 09:51:49 058 [INFO] c.a.c.QueueListener - queueList Receved:queue6
2017-05-16 09:51:49 084 [INFO] c.a.c.QueueListener - queueList Receved:queue10
2017-05-16 09:51:49 102 [INFO] c.a.c.QueueListener - queueList Receved:queue4
2017-05-16 09:51:49 140 [INFO] c.a.c.QueueListener - queueList Receved:queue100
2017-05-16 09:51:49 561 [INFO] c.a.c.QueueListener - queueList Receved:queue99
2017-05-16 09:51:49 595 [INFO] c.a.c.QueueListener - queueList Receved:queue98

很奇怪，没有按照优先级执行？文章前面已经提到，只有当消费者不足，不能及时进行消费的情况下，优先级队列才会生效。所以，我们需要先将所有的消息队列发送至服务器，然后再启动消费者处理消息，这样，就可以看到效果了。为了达到这个目的，则需要先运行主方法，然后再启动消费者，队列优先级设置和上方一样，执行结果如下：

2017-05-16 09:56:23 296 [INFO] c.a.c.QueueListener - queueList Receved:queue100
2017-05-16 09:56:23 359 [INFO] c.a.c.QueueListener - queueList Receved:queue99
2017-05-16 09:56:23 438 [INFO] c.a.c.QueueListener - queueList Receved:queue98
2017-05-16 09:56:23 500 [INFO] c.a.c.QueueListener - queueList Receved:queue10
2017-05-16 09:56:23 594 [INFO] c.a.c.QueueListener - queueList Receved:queue6
2017-05-16 09:56:23 656 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:56:23 765 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:56:23 874 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:56:24 077 [INFO] c.a.c.QueueListener - queueList Receved:queue4
2017-05-16 09:56:24 202 [INFO] c.a.c.QueueListener - queueList Receved:queue4
2017-05-16 09:56:24 262 [INFO] c.a.c.QueueListener - queueList Receved:queue3
2017-05-16 09:56:24 311 [INFO] c.a.c.QueueListener - queueList Receved:queue3
2017-05-16 09:56:24 389 [INFO] c.a.c.QueueListener - queueList Receved:queue2
2017-05-16 09:56:24 422 [INFO] c.a.c.QueueListener - queueList Receved:queue1
2017-05-16 09:56:24 500 [INFO] c.a.c.QueueListener - queueList Receved:queue1
2017-05-16 09:56:24 547 [INFO] c.a.c.QueueListener - queueList Receved:queue0

这样，优先级队列就实现了，至于相同优先级的队列，执行顺序应该是随机的吧，我也没有测试，有兴趣的同学可以自己研究。

附：队列优先级设置为：private static final int[] priority = { 1, 5, 1, 2, 9998, 3, 4, 5, 999, 5, 0, 3, 6, 10, 4, 1000, 9999, 100, 99, 98, 899 };运行结果为：

2017-05-16 09:59:29 839 [INFO] c.a.c.QueueListener - queueList Receved:queue1000
2017-05-16 09:59:29 917 [INFO] c.a.c.QueueListener - queueList Receved:queue999
2017-05-16 09:59:29 995 [INFO] c.a.c.QueueListener - queueList Receved:queue899
2017-05-16 09:59:30 073 [INFO] c.a.c.QueueListener - queueList Receved:queue100
2017-05-16 09:59:30 182 [INFO] c.a.c.QueueListener - queueList Receved:queue99
2017-05-16 09:59:30 275 [INFO] c.a.c.QueueListener - queueList Receved:queue98
2017-05-16 09:59:30 353 [INFO] c.a.c.QueueListener - queueList Receved:queue9999
2017-05-16 09:59:30 431 [INFO] c.a.c.QueueListener - queueList Receved:queue9998
2017-05-16 09:59:30 509 [INFO] c.a.c.QueueListener - queueList Receved:queue10
2017-05-16 09:59:30 619 [INFO] c.a.c.QueueListener - queueList Receved:queue6
2017-05-16 09:59:30 670 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:59:30 733 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:59:30 826 [INFO] c.a.c.QueueListener - queueList Receved:queue5
2017-05-16 09:59:31 138 [INFO] c.a.c.QueueListener - queueList Receved:queue4
2017-05-16 09:59:31 282 [INFO] c.a.c.QueueListener - queueList Receved:queue4
2017-05-16 09:59:31 316 [INFO] c.a.c.QueueListener - queueList Receved:queue3
2017-05-16 09:59:31 379 [INFO] c.a.c.QueueListener - queueList Receved:queue3
2017-05-16 09:59:31 410 [INFO] c.a.c.QueueListener - queueList Receved:queue2
2017-05-16 09:59:31 472 [INFO] c.a.c.QueueListener - queueList Receved:queue1
2017-05-16 09:59:31 712 [INFO] c.a.c.QueueListener - queueList Receved:queue1
2017-05-16 09:59:31 745 [INFO] c.a.c.QueueListener - queueList Receved:queue0

恩，排序结果是有点乱。。。