RabbitMQ笔记十四：ReturnListener

ReturnListener

mandatory

This flag tells the server how to react if the message cannot be routed to a queue.if this flag is set,the server will return an unroutable message with a return method.if this flag is zero,the server silently drops the message
如果mandatory有设置，则当消息不能路由到队列中去的时候，会触发return method。如果mandatory没有设置，则当消息不能路由到队列的时候，server会删除该消息。

immediate

This flag tell the server how to react if the message cannot be routed to a queue consumer immediately.if the flag is set ,the server will return an undeliverable message with a return method.if this flag is zero,the server will queue the message ,but with no guarantee that it will ever be consumed.
如果有设置immediate，则当消息路由到队列的时候，没有消费者的时候，会触发return method。如果immediate标识是0，则服务器就会将消息加入队列，但是不能保证这个消息能被消费。

注意
immediate属性在Rabbitmq3.x的时候，被废弃了。
因为这个关键字违背了生产者和消费者之间解耦的特性，因为生产者不关心消息是否被消费者消费掉，所以这个字段被drop掉了。

RabbitMQ java client 相关API

import com.rabbitmq.client.*;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

public class Send {
    public static void main(String[] args) throws Exception{
        ConnectionFactory connectionFactory = new ConnectionFactory();
        //或者
        connectionFactory.setUri("amqp://zhihao.miao:[email protected]:5672");

        Connection connection = connectionFactory.newConnection();

        Channel channel = connection.createChannel();

        channel.addReturnListener(new ReturnListener() {
            @Override
            public void handleReturn(int replyCode,
                                     String replyText,
                                     String exchange,
                                     String routingKey,
                                     AMQP.BasicProperties properties,
                                     byte[] body)
                    throws IOException {
                System.out.println("=========handleReturn===method============");
                System.out.println("replyText:"+replyText);
                System.out.println("exchange:"+exchange);
                System.out.println("routingKey:"+routingKey);
                System.out.println("message:"+new String(body));
            }
        });

        AMQP.BasicProperties properties = new AMQP.BasicProperties.Builder().deliveryMode(2).
                contentEncoding("UTF-8").build();

        //第三个参数是设置的mandatory
        channel.basicPublish("zhihao.direct.exchange","log.aaa",true,properties,"注册验证码".getBytes());

        TimeUnit.SECONDS.sleep(10);

        channel.close();
        connection.close();
    }
}

zhihao.direct.exchange的路由信息

因为路由不到正确的队列所以触发了ReturnListener方法的回调，控制台上打印：

replyText:NO_ROUTE
exchange:zhihao.direct.exchange
routingKey:log.aaa
message:注册验证码

spring-amqp的相关api

配置：

import org.springframework.amqp.core.Message;
import org.springframework.amqp.rabbit.connection.CachingConnectionFactory;
import org.springframework.amqp.rabbit.connection.ConnectionFactory;
import org.springframework.amqp.rabbit.core.RabbitAdmin;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MQConfig {

    @Bean
    public ConnectionFactory connectionFactory(){
        CachingConnectionFactory factory = new CachingConnectionFactory();
        factory.setUri("amqp://zhihao.miao:[email protected]:5672");
        factory.setPublisherReturns(true);
        return factory;
    }

    @Bean
    public RabbitAdmin rabbitAdmin(ConnectionFactory connectionFactory){
        RabbitAdmin rabbitAdmin = new RabbitAdmin(connectionFactory);
        return rabbitAdmin;
    }

    @Bean
    public RabbitTemplate rabbitTemplate(ConnectionFactory connectionFactory){
        RabbitTemplate rabbitTemplate = new RabbitTemplate(connectionFactory);
        rabbitTemplate.setMandatory(true);
        //rabbitTemplate.setMandatoryExpression(new SpelExpressionParser().parseExpression("(1+2) > 3")); //表达式的值为false
        rabbitTemplate.setReturnCallback(new RabbitTemplate.ReturnCallback(){
            @Override
            public void returnedMessage(Message message,
                                        int replyCode,
                                        String replyText,
                                        String exchange,
                                        String routingKey){
                System.out.println("============returnedMessage==method=========");
                System.out.println("replyCode: "+replyCode);
                System.out.println("replyText: "+replyText);
                System.out.println("exchange: "+exchange);
                System.out.println("routingKey: "+routingKey);
            }
        });
        return rabbitTemplate;
    }
}

发送消息

import org.springframework.amqp.core.MessageProperties;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;

import java.util.concurrent.TimeUnit;

@ComponentScan
public class Application {

    public static void main(String[] args) throws Exception{
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(Application.class);

        RabbitTemplate rabbitTemplate = context.getBean(RabbitTemplate.class);
        System.out.println(rabbitTemplate);

        MessageProperties messageProperties = new MessageProperties();
        messageProperties.getHeaders().put("desc","消息发送");
        messageProperties.getHeaders().put("token","234sdfsdf3r342dsfd1232");

        //路由不到指定的队列
        rabbitTemplate.convertAndSend("zhihao.direct.exchange","log.aaa","hello welcome");

        TimeUnit.SECONDS.sleep(10);

        context.close();
    }
}

zhihao.direct.exchange的路由信息

rabbitTemplate.setReturnCallback的方法会被执行，控制台打印：

============returnedMessage==method=========
replyCode: 312
replyText: NO_ROUTE
exchange: zhihao.direct.exchange
routingKey: log.aaa

总结

• 设置factory.setPublisherReturns(true);
• rabbitTemplate.setMandatory(true);或rabbitTemplate.setMandatoryExpression(new SpelExpressionParser().parseExpression("(1+2) > 2")); //表达式的值为true
  才会触发returnCallback回调方法的执行。