RabbitMQ - exchange

总结一下几种ExchangeTypes。

之前写发布/订阅模式时第一次提到了exchange type。
即producer不是将消息直接放到队列中，而是先到exchange中，exchange主要用于控制消息到队列的路由,根据具体的exchange type将消息传给需要的队列或者直接废弃。
在这一篇中总结一下那些用到的exchange type。

一.Direct Exchange
direct exchange算是最基本的了。
direct exchange用于将带上routing key的消息传值拥有相同routing key的队列中。

当我们想用一个简单的标识符区别所有传入同一个exchange中的消息时direct exchange就非常合适。

private static String DIRECT_EXCHANGE = "DIRECT_EXCHAGNE";

    static class FanoutProducer {
        public static void main(String[] args) throws IOException {
            ConnectionFactory connectionFactory = new ConnectionFactory();
            Connection connection = connectionFactory.newConnection();
            Channel channel= connection.createChannel();;

            String content = "I miss the conversation";
            channel.exchangeDeclare(DIRECT_EXCHANGE, ExchangeTypes.DIRECT);
            channel.basicPublish(DIRECT_EXCHANGE, "alvez", null, content.getBytes());
        }
    }

    static class FanoutConsumer {
        public static void main(String[] args) throws IOException, InterruptedException {
            ConnectionFactory connectionFactory = new ConnectionFactory();
            Connection connection = connectionFactory.newConnection();
            Channel channel= connection.createChannel();

            String queueName = channel.queueDeclare().getQueue();
            channel.queueBind(queueName, DIRECT_EXCHANGE, "alvez");

            QueueingConsumer consumer = new QueueingConsumer(channel);
            String s = channel.basicConsume(queueName, true, consumer);
            System.out.println(s);
            while (true) {
                QueueingConsumer.Delivery delivery = consumer.nextDelivery();
                String message = new String(delivery.getBody());
                String routingKey = delivery.getEnvelope().getRoutingKey();

                System.out.println("From:" + routingKey + "':'" + message + "'");
            }

        }
　　}

二.Fanout Exchange
fanout和routing key无关，它将消息无差别地(indiscriminately)传送给所有队列。

fanout exchange通常用于发布/订阅模式。
将消息传送给不同的队列，不同的队列对同一种消息采取不同的行为。
比如，现在有一个客户订单消息被三个队列接收，队列1完成该订单，队列2将订单写入日志，队列3将订单发给别的部门什么的。
比如下面的代码，消费者可以获得routing key并输出，但能否获取与routing key无关：

    private static String FANOUT_EXCHANGE = "FANOUT_EXCHANGE";

    static class DirectProducer {
        public static void main(String[] args) throws IOException {
            ConnectionFactory connectionFactory = new ConnectionFactory();
            Connection connection = connectionFactory.newConnection();
            Channel channel= connection.createChannel();;

            String content = "I miss the conversation";
            channel.exchangeDeclare(FANOUT_EXCHANGE, ExchangeTypes.FANOUT);
            channel.basicPublish(FANOUT_EXCHANGE, "alvez", null, content.getBytes());
        }
    }

    static class DirectConsumer {
        public static void main(String[] args) throws IOException, InterruptedException {
            ConnectionFactory connectionFactory = new ConnectionFactory();
            Connection connection = connectionFactory.newConnection();
            Channel channel= connection.createChannel();

            String queueName = channel.queueDeclare().getQueue();
            channel.queueBind(queueName, FANOUT_EXCHANGE, "");

            QueueingConsumer consumer = new QueueingConsumer(channel);
            String s = channel.basicConsume(queueName, true, consumer);
            System.out.println(s);
            while (true) {
                QueueingConsumer.Delivery delivery = consumer.nextDelivery();
                String message = new String(delivery.getBody());
                String routingKey = delivery.getEnvelope().getRoutingKey();

                System.out.println("From:" + routingKey + "':'" + message + "'");
            }

        }

    }

三.Topic Exchange
如果根据topic exchange用法说明其特征的话反而更麻烦。
topic exchange正如其名，就是根据某种主题而不是特定的标题，也就是可以匹配routing key的一部分或者全部。
topic exchange的routing key可以有多个词组成，词用'.'分隔。
routing key中可以包括'*'或者'#'，'*'表示一个词，'#'表示0～N个词。

比如消息发布时routing key为"honda.civic.navy"，
能接收消息的队列的routing key可以是"honda.civic.navy"或"*.civic.*"或"honda.#"或"#"，
但不能是"honda.accord.navy"或"honda.accord.silver"或"*.accord.*"或"ford.#"。

    private static String TOPIC_EXCHANGE = "TOPIC_EXCHAGNE";

    static class TopicProducer {
        public static void main(String[] args) throws IOException {
            ConnectionFactory connectionFactory = new ConnectionFactory();
            Connection connection = connectionFactory.newConnection();
            Channel channel= connection.createChannel();;

            String content = "I miss the conversation";
            channel.exchangeDeclare(TOPIC_EXCHANGE, ExchangeTypes.TOPIC);
            channel.basicPublish(TOPIC_EXCHANGE, "alvez.dep.FBI.map", null, content.getBytes());
        }
    }

    static class TopicConsumer {
        public static void main(String[] args) throws IOException, InterruptedException {
            ConnectionFactory connectionFactory = new ConnectionFactory();
            Connection connection = connectionFactory.newConnection();
            Channel channel= connection.createChannel();

            String queueName = channel.queueDeclare().getQueue();
            channel.queueBind(queueName, TOPIC_EXCHANGE, "alvez.#");

            QueueingConsumer consumer = new QueueingConsumer(channel);
            String s = channel.basicConsume(queueName, true, consumer);
            System.out.println(s);
            while (true) {
                QueueingConsumer.Delivery delivery = consumer.nextDelivery();
                String message = new String(delivery.getBody());
                String routingKey = delivery.getEnvelope().getRoutingKey();

                System.out.println("From:" + routingKey + "':'" + message + "'");
            }

        }
　　}

四.Headers Exchange
即消息头和队列中声明的消息头匹配时可以通信，似乎不是很常用。
就可以定义多个条件进行匹配这一点来说，headers exchange和topic exchange有些相似。
有时候会给人"为什么会有这种东西?"的感觉，相比topic exchage有什么优势?
如果仅仅说"headers exchange是基于headers的，topic exchange是基于routing key的"，这种回答没什么意义。

代码如下，可以看到producer和consumer的routing key是不同的，producer的header通过properties对象传输：

　　private static String HEADERS_EXCHANGE = "HEADERS_EXCHANGE";

    static class HeadersProducer {
        public static void main(String[] args) throws IOException {
            ConnectionFactory connectionFactory = new ConnectionFactory();
            Connection connection = connectionFactory.newConnection();
            Channel channel = connection.createChannel();

            String content = "I miss the conversation";
            channel.exchangeDeclare(HEADERS_EXCHANGE, ExchangeTypes.HEADERS);
            AMQP.BasicProperties properties = new AMQP.BasicProperties();
            Map<String,Object> map = new HashMap<>();
            map.put("key1","val1");
            properties.setHeaders(map);

            channel.basicPublish(HEADERS_EXCHANGE, "alvez", properties, content.getBytes());

        }
    }

    static class HeadersConsumer {
        public static void main(String[] args) throws IOException, InterruptedException {
            ConnectionFactory connectionFactory = new ConnectionFactory();
            Connection connection = connectionFactory.newConnection();
            Channel channel = connection.createChannel();

            String queueName = channel.queueDeclare().getQueue();
            Map<String, Object> headers = new HashMap<>();
            headers.put("key1","val1");
            headers.put("key2","val2");
            headers.put("key3","val3");
            headers.put("key4","val4");
            channel.queueBind(queueName, HEADERS_EXCHANGE, "",headers);

            QueueingConsumer consumer = new QueueingConsumer(channel);
            String s = channel.basicConsume(queueName, true, consumer);
            System.out.println(s);
            while (true) {
                QueueingConsumer.Delivery delivery = consumer.nextDelivery();
                String message = new String(delivery.getBody());
                String routingKey = delivery.getEnvelope().getRoutingKey();

                System.out.println("From:" + routingKey + "':'" + message + "'");
            }

        }

    }

(ps:图不错，感谢图片作者。)