RabbitMQ 中的交换机学习

一、直接交换机（Direct Exchange）
1. 介绍
Direct 交换机将消息路由到绑定了指定 Routing Key 的队列中。每条消息都有一个 Routing Key，当队列绑定到 Direct 交换机时，它需要一个指定的 Routing Key。只有消息的 Routing Key 与队列绑定的 Routing Key 完全匹配时，消息才会路由到该队列中。

2. 代码示例
- 发送消息
public class DirectLogs {
public static final String exchange_name = "direct_logs";
public static void main(String[] args) throws Exception {
Channel channel = RabbitMqUtils.getChannel();
Scanner sc = new Scanner(System.in);
while(sc.hasNext()){
String message = sc.next();
channel.basicPublish(exchange_name, "error", null, message.getBytes("UTF-8"));
System.out.println("生产者发送消息：" + message);
}
}
}

- 接收消息
public class ReceiveLogsTopic01 {
public static final String EXCHANGE_NAME = "direct_logs";
public static final String QUEUE_NAME = "console";
public static void main(String[] args) throws Exception {
Channel channel = RabbitMqUtils.getChannel();
channel.exchangeDeclare(EXCHANGE_NAME, BuiltinExchangeType.DIRECT);
channel.queueDeclare(QUEUE_NAME, false, false, false, null);
channel.queueBind(QUEUE_NAME, EXCHANGE_NAME, "info");
channel.queueBind(QUEUE_NAME, EXCHANGE_NAME, "warning");

DeliverCallback deliverCallback = (consumerTag, message) -> {
System.out.println("ReceiveLogsTopic01接收到的消息：" + new String(message.getBody(), "UTF-8"));
};
channel.basicConsume(QUEUE_NAME, true, deliverCallback, consumerTag -> {});
}
}

- 结果
消息通过 Direct 交换机路由到对应队列：

二、主题交换机（Topic Exchange）
1. 介绍
Topic 交换机是基于通配符进行路由的交换机。它允许队列绑定的 Routing Key 使用 *（匹配一个词）和 #（匹配零个或多个词）作为通配符。它适用于需要模糊匹配的场景，例如日志系统。

2. 代码示例
- 发送消息
public class EmitLog {
public static final String exchange_name = "topic_logs";
public static void main(String[] args) throws Exception {
Channel channel = RabbitMqUtils.getChannel();
Map<String, String> bindingKeyMap = new HashMap<>();
bindingKeyMap.put("quick.orange.rabbit", "被队列 Q1Q2 接收到");
bindingKeyMap.put("lazy.orange.elephant", "被队列 Q1Q2 接收到");
bindingKeyMap.put("quick.orange.fox", "被队列 Q1 接收到");
bindingKeyMap.put("lazy.brown.fox", "被队列 Q2 接收到");
bindingKeyMap.put("lazy.pink.rabbit", "虽然满足两个绑定但只被队列 Q2 接收一次");

for (Map.Entry<String, String> entry : bindingKeyMap.entrySet()) {
String key = entry.getKey();
String message = entry.getValue();
channel.basicPublish(exchange_name, key, null, message.getBytes("UTF-8"));
System.out.println("生产者发出消息：" + message);
}
}
}

- 接收消息
public class ReceiveLogsTopic01 {
public static final String exchange_name = "topic_logs";
public static void main(String[] args) throws Exception {
Channel channel = RabbitMqUtils.getChannel();
channel.exchangeDeclare(exchange_name, "topic");
String queue_name = "Q1";
channel.queueDeclare(queue_name, false, false, false, null);
channel.queueBind(queue_name, exchange_name, "*.orange.*");

DeliverCallback deliverCallback = (consumerTag, message) -> {
System.out.println("接收到的消息：" + new String(message.getBody(), "UTF-8"));
System.out.println("接收队列：" + queue_name + " 绑定键：" + message.getEnvelope().getRoutingKey());
};
channel.basicConsume(queue_name, true, deliverCallback, consumerTag -> {});
}
}

三、扇出交换机（Fanout Exchange）
1. 介绍
Fanout 交换机是最简单的交换机类型，它会将消息广播给所有与之绑定的队列，而不考虑消息的 Routing Key。通常用于广播消息，比如多服务实例之间的消息同步。

2. 代码示例
- 发送消息
public class EmitLog {
public static final String exchange_name = "logs";
public static void main(String[] args) throws Exception {
Channel channel = RabbitMqUtils.getChannel();
channel.exchangeDeclare(exchange_name, "fanout");
Scanner sc = new Scanner(System.in);
while(sc.hasNext()){
String message = sc.next();
channel.basicPublish(exchange_name, "", null, message.getBytes());
System.out.println("生产者发送消息：" + message);
}
}
}

- 接收消息
public class ReceiveLog01 {
public static final String exchange_name = "logs";
public static void main(String[] args) throws Exception {
Channel channel = RabbitMqUtils.getChannel();
channel.exchangeDeclare(exchange_name, "fanout");
String queueName = channel.queueDeclare().getQueue();
channel.queueBind(queueName, exchange_name, "");

DeliverCallback deliverCallback = (consumerTag, message) -> {
System.out.println("接收到的消息：" + new String(message.getBody(), "UTF-8"));
};
channel.basicConsume(queueName, true, deliverCallback, consumerTag -> {});
}
}

小结
Direct Exchange：消息通过精确匹配的 Routing Key 路由到绑定的队列。
Topic Exchange：消息通过通配符匹配的 Routing Key 路由到队列，适用于模糊匹配场景。
Fanout Exchange：消息会被广播给所有与之绑定的队列，不考虑 Routing Key，适用于广播场景。
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原文链接：https://blog.csdn.net/dhrmt/article/details/143099569