一、rabbitmq實現rpc呼叫的原理

·rabbitmq實現rpc的原理是：客戶端向一個佇列中傳送訊息，並註冊一個回撥的佇列用於接收服務端返回的訊息，該訊息需要宣告一個叫做correaltionId的屬性，該屬性將是該次請求的唯一標識。服務端在接受到訊息（在需要時可以驗證correaltionId）後，處理訊息，並將訊息傳送到客戶端註冊的回撥佇列中。原理圖如下：　　

二、程式碼實現

　　下面我們將模擬實現一個rpc客戶端和rpc服務端。客戶端給服務端傳送message，服務端收到後處理message，再將處理後的訊息返給客戶端

　　rpc客戶端

/**
 * rpc客戶端
 
 
*/
public class RpcClient {
    //傳送訊息的佇列名稱
    private static final String RPC_QUEUE_NAME = "rpc_queue";

    public static void main(String[] args) {
        ConnectionFactory connectionFactory = new ConnectionFactory();
        Connection connection = null;
        Channel channel = null;
        try
 
 {
           connection = connectionFactory.newConnection();
           channel = connection.createChannel();
           //建立回撥佇列
           String callbackQueue = channel.queueDeclare().getQueue();
           //建立回撥佇列，消費者從回撥佇列中接收服務端傳送的訊息
            QueueingConsumer consumer = new QueueingConsumer(channel);
            channel.basicConsume(callbackQueue,
 
true,consumer);

            //建立訊息帶有correlationId的訊息屬性
            String correlationId = UUID.randomUUID().toString();
            AMQP.BasicProperties basicProperties = new AMQP.BasicProperties().builder().correlationId(correlationId).replyTo(callbackQueue).build();
            String message = "hello rabbitmq";
            channel.basicPublish("",RPC_QUEUE_NAME,basicProperties,message.getBytes());
            System.out.println("RpcClient send message " + message + ", correaltionId = " + correlationId);

            //接收回調訊息
            while (true){
                QueueingConsumer.Delivery delivery = consumer.nextDelivery();
                String receivedCorrelationId = delivery.getProperties().getCorrelationId();
                if(correlationId.equals(receivedCorrelationId)){
                    System.out.println("RpcClient receive format message " + new String(delivery.getBody(), "UTF-8") + ", correaltionId = " + correlationId);
                    break;
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            try {
                channel.close();
                connection.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }
}

 　　rpc服務端

/**
 * rpc伺服器
 */
public class RpcServer {
    private static final String RPC_QUEUE_NAME = "rpc_queue";

    private static String format(String message){
        return "......" + message + "......";
    }

    public static void main(String[] args) {
        ConnectionFactory connectionFactory = new ConnectionFactory();
        Connection connection = null;
        try {
            connection = connectionFactory.newConnection();
            Channel channel = connection.createChannel();
            channel.queueDeclare(RPC_QUEUE_NAME,false,false,false,null);
            QueueingConsumer consumer = new QueueingConsumer(channel);
            //宣告消費者預取的訊息數量
            channel.basicQos(1);
            channel.basicConsume(RPC_QUEUE_NAME,false,consumer);//採用手動回覆訊息
            System.out.println("RpcServer waitting for receive message");

            while (true){
                //接收並處理訊息
                QueueingConsumer.Delivery delivery = consumer.nextDelivery();
                String message = new String(delivery.getBody(), "UTF-8");
                System.out.println("RpcServer receive message " + message);
                String response = format(message);
                //確認收到訊息
                channel.basicAck(delivery.getEnvelope().getDeliveryTag(),false);

                //取出訊息的correlationId
                AMQP.BasicProperties properties = delivery.getProperties();
                String correlationId = properties.getCorrelationId();

                //建立具有與接收訊息相同的correlationId的訊息屬性
                AMQP.BasicProperties replyProperties = new AMQP.BasicProperties().builder().correlationId(correlationId).build();
                channel.basicPublish("",properties.getReplyTo(),replyProperties,response.getBytes());
            }

        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

 　　先執行服務端，再執行客戶端，結果如下：

　　RpcClient

　　RpcServer