深入学习RabbitMQ(一):mandatory标志的作用

smallswan 发布于4月前 阅读1992次
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        在生产者通过channel的basicPublish方法发布消息时,通常有几个参数需要设置,为此我们有必要了解清楚这些参数代表的具体含义及其作用,查看Channel接口,会发现存在3个重载的basicPublish方法

 

void basicPublish(String exchange, String routingKey, BasicProperties props, byte[] body) throws IOException;

void basicPublish(String exchange, String routingKey, boolean mandatory, BasicProperties props, byte[] body)
            throws IOException;

void basicPublish(String exchange, String routingKey, boolean mandatory, boolean immediate, BasicProperties props, byte[] body)
            throws IOException;

 

        他们共有的参数分别是:
        exchange:交换机名称
        routingKey:路由键
        props:消息属性字段,比如消息头部信息等等
        body:消息主体部分
        除此之外,还有mandatory和immediate这两个参数,鉴于RabbitMQ3.0不再支持immediate标志,因此我们重点讨论mandatory标志
        mandatory的作用:

 

        当mandatory标志位设置为true时,如果exchange根据自身类型和消息routingKey无法找到一个合适的queue存储消息,那么broker会调用basic.return方法将消息返还给生产者;当mandatory设置为false时,出现上述情况broker会直接将消息丢弃;通俗的讲,mandatory标志告诉broker代理服务器至少将消息route到一个队列中,否则就将消息return给发送者;

       下面我们通过几个实例测试下mandatory标志的作用:
        测试1:设置mandatory标志,且exchange未绑定队列

 

public class ProducerTest {
	public static void main(String[] args) {
		String exchangeName = "confirmExchange";
		String queueName = "confirmQueue";
		String routingKey = "confirmRoutingKey";
		String bindingKey = "confirmBindingKey";
		int count = 3;
		
		ConnectionFactory factory = new ConnectionFactory();
		factory.setHost("172.16.151.74");
		factory.setUsername("test");
		factory.setPassword("test");
		factory.setPort(5672);
		
		//创建生产者
		Sender producer = new Sender(factory, count, exchangeName, routingKey);
		producer.run();
	}
}

class Sender
{
	private ConnectionFactory factory;
	private int count;
	private String exchangeName;
	private String routingKey;
	
	public Sender(ConnectionFactory factory,int count,String exchangeName,String routingKey) {
		this.factory = factory;
		this.count = count;
		this.exchangeName = exchangeName;
		this.routingKey = routingKey;
	}
	
	public void run() {
		try {
			Connection connection = factory.newConnection();
			Channel channel = connection.createChannel();
			//创建exchange
			channel.exchangeDeclare(exchangeName, "direct", true, false, null);
			//发送持久化消息
			for(int i = 0;i < count;i++)
			{
				//第一个参数是exchangeName(默认情况下代理服务器端是存在一个""名字的exchange的,因此如果不创建exchange的话我们可以直接将该参数设置成"",如果创建了exchange的话我们需要将该参数设置成创建的exchange的名字),第二个参数是路由键
				channel.basicPublish(exchangeName, routingKey, true, MessageProperties.PERSISTENT_BASIC, ("第"+(i+1)+"条消息").getBytes());
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

       第45行我们将basicPublish的第三个参数mandatory设置成了true,表示开启了mandatory标志,但我们没有为当前exchange绑定任何队列;

       通过wireshark抓包看到下面输出: 

       可以看到最后执行了basic.return方法,将发布者发出的消息返还给了发布者,查看协议的Arguments参数部分可以看到,Reply-Text字段值为:NO_ROUTE,表示消息并没有路由到合适的队列中;

       那么我们该怎么获取到没有被正确路由到合适队列的消息呢?这时候可以通过为channel信道设置ReturnListener监听器来实现,具体实现代码见下:

 

public class ProducerTest {
	public static void main(String[] args) {
		String exchangeName = "confirmExchange";
		String queueName = "confirmQueue";
		String routingKey = "confirmRoutingKey";
		String bindingKey = "confirmBindingKey";
		int count = 3;
		
		ConnectionFactory factory = new ConnectionFactory();
		factory.setHost("172.16.151.74");
		factory.setUsername("test");
		factory.setPassword("test");
		factory.setPort(5672);
		
		//创建生产者
		Sender producer = new Sender(factory, count, exchangeName, routingKey);
		producer.run();
	}
}

class Sender
{
	private ConnectionFactory factory;
	private int count;
	private String exchangeName;
	private String routingKey;
	
	public Sender(ConnectionFactory factory,int count,String exchangeName,String routingKey) {
		this.factory = factory;
		this.count = count;
		this.exchangeName = exchangeName;
		this.routingKey = routingKey;
	}
	
	public void run() {
		try {
			Connection connection = factory.newConnection();
			Channel channel = connection.createChannel();
			//创建exchange
			channel.exchangeDeclare(exchangeName, "direct", true, false, null);
			//发送持久化消息
			for(int i = 0;i < count;i++)
			{
				//第一个参数是exchangeName(默认情况下代理服务器端是存在一个""名字的exchange的,
				//因此如果不创建exchange的话我们可以直接将该参数设置成"",如果创建了exchange的话
				//我们需要将该参数设置成创建的exchange的名字),第二个参数是路由键
				channel.basicPublish(exchangeName, routingKey, true, MessageProperties.PERSISTENT_BASIC, ("第"+(i+1)+"条消息").getBytes());
			}
			channel.addReturnListener(new ReturnListener() {
				
				@Override
				public void handleReturn(int arg0, String arg1, String arg2, String arg3, BasicProperties arg4, byte[] arg5)
						throws IOException {
					//此处便是执行Basic.Return之后回调的地方
					String message = new String(arg5);
					System.out.println("Basic.Return返回的结果:  "+message);
				}
			});
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

       在设置了ReturnListener监听器之后,broker(代理服务器)发出basic.return方法之后,就会回调第52行的handleReturn方法,在这个方法里面我们就可以进行消息的重新发布操作啦;

       测试2:设置mandatory标志,且为exchange绑定队列(路由键和绑定键一致)

 

public class ProducerTest {
	public static void main(String[] args) {
		String exchangeName = "confirmExchange";
		String queueName = "confirmQueue";
		String routingKey = "confirmRoutingKey";
		String bindingKey = "confirmRoutingKey";
		//String bindingKey = "confirmBindingKey";
		int count = 3;
		
		ConnectionFactory factory = new ConnectionFactory();
		factory.setHost("172.16.151.74");
		factory.setUsername("test");
		factory.setPassword("test");
		factory.setPort(5672);
		
		//创建生产者
		Sender producer = new Sender(factory, count, exchangeName, queueName,routingKey,bindingKey);
		producer.run();
	}
}

class Sender
{
	private ConnectionFactory factory;
	private int count;
	private String exchangeName;
	private String 	queueName;
	private String routingKey;
	private String bindingKey;
	
	public Sender(ConnectionFactory factory,int count,String exchangeName,String queueName,String routingKey,String bindingKey) {
		this.factory = factory;
		this.count = count;
		this.exchangeName = exchangeName;
		this.queueName = queueName;
		this.routingKey = routingKey;
		this.bindingKey = bindingKey;
	}
	
	public void run() {
		try {
			Connection connection = factory.newConnection();
			Channel channel = connection.createChannel();
			//创建exchange
			channel.exchangeDeclare(exchangeName, "direct", true, false, null);
			//创建队列
			channel.queueDeclare(queueName, true, false, false, null);
			//绑定exchange和queue
			channel.queueBind(queueName, exchangeName, bindingKey);
			//发送持久化消息
			for(int i = 0;i < count;i++)
			{
				//第一个参数是exchangeName(默认情况下代理服务器端是存在一个""名字的exchange的,
				//因此如果不创建exchange的话我们可以直接将该参数设置成"",如果创建了exchange的话
				//我们需要将该参数设置成创建的exchange的名字),第二个参数是路由键
				channel.basicPublish(exchangeName, routingKey, true, MessageProperties.PERSISTENT_BASIC, ("第"+(i+1)+"条消息").getBytes());
			}
			channel.addReturnListener(new ReturnListener() {
				
				@Override
				public void handleReturn(int arg0, String arg1, String arg2, String arg3, BasicProperties arg4, byte[] arg5)
						throws IOException {
					//此处便是执行Basic.Return之后回调的地方
					String message = new String(arg5);
					System.out.println("Basic.Return返回的结果:  "+message);
				}
			});
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

        通过抓包发现并不会有basic.return方法被调用,查看RabbitMQ管理界面发现消息已经到达了队列;


 

        测试3:设置mandatory标志,且exchange绑定队列(路由键和绑定键不一致)

        代码就是把测试2中第6行注释,第7行注释打开,注意到此时的routingKey和bindingKey是不一致的,此时我们运行程序,同时抓包得到下面截图:

       注意一点,我们发送了三条消息,那么相应的应该执行三次basic.return,其中第一次和第二次basic.return显示在一行上了,第三次是单独一行,不要误认为只执行了两次,从协议的具体返回内容里我们同样看到了Reply-Text字段值是NO_ROUTE,这种现象在测试1中已经见过了;

       到此,我们明白了mandatory标志的作用:在消息没有被路由到合适队列情况下会将消息返还给消息发布者,同时我们测试了哪些情况下消息不会到达合适的队列,测试1演示的是创建了exchange但是没有为他绑定队列导致的消息未到达合适队列,测试3演示的是创建了exchange同时创建了queue,但是在将两者绑定的时候,使用的bindingKey和消息发布者使用的rountingKey不一致导致的消息未到达合适队列;

       参考资料:

       RabbitMQ(二) AMQP协议mandatory和immediate标志位区别

       RabbitMQ之mandatory

 

 

 

 

 

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