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交换机

**交换机 **是消息队列中的一个组件，其作用类似于网络路由器。它负责将我们发送的消息转发到相应的目标，就像快递站将快递发送到对应的站点，或者网络路由器将网络请求转发到相应的服务器或客户端一样。交换机的主要功能是提供转发消息的能力，根据消息的路由规则将消息投递到合适的队列或绑定的消费者。
我们可以理解为，如果说一个快递站已经承受不了那么多的快递了，就建多个快递站。

fanout

扇出，广播
特点：消息会被转发到所有绑定到该交换机的队列
场景:很适用于发布订阅的场景，比如写日志，可以多个系统间共享

示例场景：

生产者代码：

package com.yupi.springbootinit.mq;import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;import java.util.Scanner;public class FanoutProducer {// 交换机名字private static final String EXCHANGE_NAME = "fanout-exchange";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");try (Connection connection = factory.newConnection();Channel channel = connection.createChannel()) {// 创建交换机channel.exchangeDeclare(EXCHANGE_NAME, "fanout");Scanner scanner = new Scanner(System.in);while (scanner.hasNext()) {String message = scanner.nextLine();channel.basicPublish(EXCHANGE_NAME, "", null, message.getBytes("UTF-8"));System.out.println(" [x] Sent '" + message + "'");}}}
}

消费者代码：

package com.yupi.springbootinit.mq;import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.DeliverCallback;public class FanoutConsumer {//交换机名字private static final String EXCHANGE_NAME = "fanout-exchange";public static void main(String[] argv) throws Exception {//建立连接ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");Connection connection = factory.newConnection();//创建频道Channel channel1 = connection.createChannel();// 声明交换机channel1.exchangeDeclare(EXCHANGE_NAME, "fanout");// 创建队列1，连接到交换机上String queueName = "xiaowang_queue";channel1.queueDeclare(queueName, true, false, false, null);channel1.queueBind(queueName, EXCHANGE_NAME, "");// 创建队列2,连接到交换机上String queueName2 = "xiaoli_queue";channel1.queueDeclare(queueName2, true, false, false, null);channel1.queueBind(queueName2, EXCHANGE_NAME, "");System.out.println(" [*] Waiting for messages. To exit press CTRL+C");// 创建交付回调函数1DeliverCallback deliverCallback1 = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [小王] Received '" + message + "'");};// 创建交付回调函数2DeliverCallback deliverCallback2 = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [小李] Received '" + message + "'");};// 开始消费消息队列1channel1.basicConsume(queueName, true, deliverCallback1, consumerTag -> { });// 开始消费消息队列2channel1.basicConsume(queueName2, true, deliverCallback2, consumerTag -> { });}
}

Direct

官方教程：https://www.rabbitmq.com/tutorials/tutorial-four-java.html
特点：消息会根据路由键转发到指定的队列
场景：特定的消息只交给特定的系统（程序）来处理

注意：不同队列可以绑定相同的路由键

示例场景：
老板在发送消息同时会带上路由键，根据路由键找对应的队列来发送

生产者代码：

package com.yupi.springbootinit.mq;import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;import java.util.Scanner;public class DirectProducer {private static final String EXCHANGE_NAME = "direct-exchange";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");try (Connection connection = factory.newConnection();Channel channel = connection.createChannel()) {//声明交换机是directchannel.exchangeDeclare(EXCHANGE_NAME, "direct");//输入消息 和 路由键Scanner scanner = new Scanner(System.in);while (scanner.hasNext()) {String userInput = scanner.nextLine();String[] strings = userInput.split(" ");if (strings.length < 1) {continue;}String message = strings[0];String routingKey = strings[1];//发布消息的时候注意指定路由键channel.basicPublish(EXCHANGE_NAME, routingKey, null, message.getBytes("UTF-8"));System.out.println(" [x] Sent '" + message + " with routing:" + routingKey + "'");}}}
}

消费者代码：

package com.yupi.springbootinit.mq;import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.DeliverCallback;public class DirectConsumer {private static final String EXCHANGE_NAME = "direct-exchange";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");Connection connection = factory.newConnection();Channel channel = connection.createChannel();//声明交换机，不过生成者已经声明过了，消费者声不声明都可以channel.exchangeDeclare(EXCHANGE_NAME, "direct");// 创建队列String queueName = "xiaoyu_queue";channel.queueDeclare(queueName, true, false, false, null);channel.queueBind(queueName, EXCHANGE_NAME, "xiaoyu"); //指定2交换机和路由键// 创建队列，随机分配一个队列名称String queueName2 = "xiaopi_queue";channel.queueDeclare(queueName2, true, false, false, null);channel.queueBind(queueName2, EXCHANGE_NAME, "xiaopi");System.out.println(" [*] Waiting for messages. To exit press CTRL+C");DeliverCallback xiaoyuDeliverCallback = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [xiaoyu] Received '" +delivery.getEnvelope().getRoutingKey() + "':'" + message + "'");};DeliverCallback xiaopiDeliverCallback = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [xiaopi] Received '" +delivery.getEnvelope().getRoutingKey() + "':'" + message + "'");};channel.basicConsume(queueName, true, xiaoyuDeliverCallback, consumerTag -> {});channel.basicConsume(queueName2, true, xiaopiDeliverCallback, consumerTag -> {});}
}

topic

官方教程：https://www.rabbitmq.com/tutorials/tutorial-five-java.html
特点：消息会根据一个模糊的路由键转发到指定的队列
场景:特定的一类消息可以交给特定的一类系统（程序）来处理
规则：

1. :匹配一个单词，比如.orange，那么 abc.orange、ikun.orange 都能匹配
2. #:匹配0个或多个单词，比如orange.#，那么orange，orange.abc.ikun都能匹配

应用场景：
老板要下发一个任务，让多个组来处理

生产者代码：

package com.yupi.springbootinit.mq;import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;import java.util.Scanner;public class TopicProducer {private static final String EXCHANGE_NAME = "topic-exchange";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");try (Connection connection = factory.newConnection();Channel channel = connection.createChannel()) {channel.exchangeDeclare(EXCHANGE_NAME, "topic");Scanner scanner = new Scanner(System.in);while (scanner.hasNext()) {String userInput = scanner.nextLine();String[] strings = userInput.split(" ");if (strings.length < 1) {continue;}String message = strings[0];String routingKey = strings[1];channel.basicPublish(EXCHANGE_NAME, routingKey, null, message.getBytes("UTF-8"));System.out.println(" [x] Sent '" + message + " with routing:" + routingKey + "'");}}}
}

消费者代码：

package com.yupi.springbootinit.mq;import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.DeliverCallback;public class TopicConsumer {private static final String EXCHANGE_NAME = "topic-exchange";public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");Connection connection = factory.newConnection();Channel channel = connection.createChannel();channel.exchangeDeclare(EXCHANGE_NAME, "topic");// 创建队列String queueName = "frontend_queue";channel.queueDeclare(queueName, true, false, false, null);channel.queueBind(queueName, EXCHANGE_NAME, "#.前端.#");// 创建队列String queueName2 = "backend_queue";channel.queueDeclare(queueName2, true, false, false, null);channel.queueBind(queueName2, EXCHANGE_NAME, "#.后端.#");// 创建队列String queueName3 = "product_queue";channel.queueDeclare(queueName3, true, false, false, null);channel.queueBind(queueName3, EXCHANGE_NAME, "#.产品.#");System.out.println(" [*] Waiting for messages. To exit press CTRL+C");DeliverCallback xiaoaDeliverCallback = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [xiaoa] Received '" +delivery.getEnvelope().getRoutingKey() + "':'" + message + "'");};DeliverCallback xiaobDeliverCallback = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [xiaob] Received '" +delivery.getEnvelope().getRoutingKey() + "':'" + message + "'");};DeliverCallback xiaocDeliverCallback = (consumerTag, delivery) -> {String message = new String(delivery.getBody(), "UTF-8");System.out.println(" [xiaoc] Received '" +delivery.getEnvelope().getRoutingKey() + "':'" + message + "'");};channel.basicConsume(queueName, true, xiaoaDeliverCallback, consumerTag -> {});channel.basicConsume(queueName2, true, xiaobDeliverCallback, consumerTag -> {});channel.basicConsume(queueName3, true, xiaocDeliverCallback, consumerTag -> {});}
}

这样生产者发消息：前端.后端

就可以匹配到前端和后端两个队列

Headers

可以根据headers中的内容来指定发送到哪个队列，由于性能差，比较复杂，一般不推荐使用

RPC

支持用消息队列来模拟RPC的调用，但是一般没必要，直接用 Dubbo、GRPC 等 RPC 框架就好了。