RabbitMQ 笔记-RPC

RabbitMQ中实现RPC的机制是：

• 客户端发送请求（消息）时，在消息的属性（MessageProperties，在AMQP协议中定义了14中properties，这些属性会随着消息一起发送）中设置两个值replyTo（一个Queue名称，用于告诉服务器处理完成后将通知我的消息发送到这个Queue中）和correlationId（此次请求的标识号，服务器处理完成后需要将此属性返还，客户端将根据这个id了解哪条请求被成功执行了或执行失败）
• 服务器端收到消息并处理
• 服务器端处理完消息后，将生成一条应答消息到replyTo指定的Queue，同时带上correlationId属性
• 客户端之前已订阅replyTo指定的Queue，从中收到服务器的应答消息后，根据其中的correlationId属性分析哪条请求被执行了，根据执行结果进行后续业务处理

public class RPCClient {

    private static final String RPC_QUEUE_NAME = "rpc_queue";

    private Connection connection;
    private Channel channel;
    private String replyQueueName;
    private QueueingConsumer consumer;

    public RPCClient() throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        // 设置MabbitMQ所在主机ip或者主机名
        factory.setHost("192.168.65.136");
        factory.setUsername("rabbitmq");
        factory.setPassword("123456");
        // 创建一个连接
        connection = factory.newConnection();
        // 创建一个频道
        channel = connection.createChannel();

        //声明队列
        channel.queueDeclare(RPC_QUEUE_NAME, false, false, false, null);

        //为每一个客户端获取一个随机的回调队列
        replyQueueName = channel.queueDeclare().getQueue();
        //为每一个客户端创建一个消费者（用于监听回调队列，获取结果）
        consumer = new QueueingConsumer(channel);
        //消费者与队列关联
        channel.basicConsume(replyQueueName, true, consumer);
    }

    /**
     * 获取斐波列其数列的值
     *
     * @param message
     * @return
     * @throws Exception
     */
    public String call(String message) throws Exception{
        String response = null;
        String corrId = java.util.UUID.randomUUID().toString();

        //设置replyTo和correlationId属性值
        BasicProperties props = new BasicProperties.Builder().correlationId(corrId).replyTo(replyQueueName).build();

        //发送消息到rpc_queue队列
        channel.basicPublish("", RPC_QUEUE_NAME, props, message.getBytes());

        while (true) {
            System.out.println("OK?");
            QueueingConsumer.Delivery delivery = consumer.nextDelivery();
            System.out.println("OK");
            if (delivery.getProperties().getCorrelationId().equals(corrId)) {
                response = new String(delivery.getBody(),"UTF-8");
                break;
            }
        }

        return response;
    }

    public static void main(String[] args) throws Exception {
        RPCClient fibonacciRpc = new RPCClient();
        String result = fibonacciRpc.call("4");
        System.out.println( "fib(4) is " + result);
    }
}

public class RPCServer {

    private static final String RPC_QUEUE_NAME = "rpc_queue";

    public static void main(String[] args) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        // 设置MabbitMQ所在主机ip或者主机名
        factory.setHost("192.168.65.136");
        factory.setUsername("rabbitmq");
        factory.setPassword("123456");
        // 创建一个连接
        Connection connection = factory.newConnection();
        // 创建一个频道
        Channel channel = connection.createChannel();

        //声明队列
        channel.queueDeclare(RPC_QUEUE_NAME, false, false, false, null);

        //限制：每次最多给一个消费者发送1条消息
        channel.basicQos(1);

        //为rpc_queue队列创建消费者，用于处理请求
        QueueingConsumer consumer = new QueueingConsumer(channel);
        channel.basicConsume(RPC_QUEUE_NAME, false, consumer);

        System.out.println(" [x] Awaiting RPC requests");

        while (true) {
            QueueingConsumer.Delivery delivery = consumer.nextDelivery();

            //获取请求中的correlationId属性值，并将其设置到结果消息的correlationId属性中
            BasicProperties props = delivery.getProperties();
            BasicProperties replyProps = new BasicProperties.Builder().correlationId(props.getCorrelationId()).build();
            //获取回调队列名字
            String callQueueName = props.getReplyTo();

            String message = new String(delivery.getBody(),"UTF-8");

            System.out.println(" [.] fib(" + message + ")");

            //获取结果
            String response = "" + fib(Integer.parseInt(message));
            //先发送回调结果
            channel.basicPublish("", callQueueName, replyProps,response.getBytes());
            //后手动发送消息反馈
            channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
        }
    }

    /**
     * 计算斐波列其数列的第n项
     *
     * @param n
     * @return
     * @throws Exception
     */
    private static int fib(int n) throws Exception {
        if (n < 0)
            throw new Exception("参数错误，n必须大于等于0");
        if (n == 0)
            return 0;
        if (n == 1)
            return 1;
        return fib(n - 1) + fib(n - 2);
    }
}