rabbitMQ學習筆記(七) RPC 遠程過程調用

關於RPC的介紹請參考百度百科里的關於RPC的介紹：http://baike.baidu.com/view/32726.htm#sub32726

   現在來看看Rabbitmq中RPC吧！RPC的工作示意圖如下：

   上圖中的C代表客戶端，S表示服務器端；Rabbitmq中的RPC流程如下：

1、首先客戶端發送一個reply_to和corrention_id的請求,發布到RPC隊列中；

2、服務器端處理這個請求，並把處理結果發布到一個回調Queue,此Queue的名稱應當與reply_to的名稱一致

3、客戶端從回調Queue中得到先前correlation_id設定的值的處理結果。如果碰到和先前不一樣的corrention_id的值，將會忽略而不是拋出異常。

 

  對於上面所提到的回調Queue中的消費處理使用的是BasicProperties類；而消息 屬性在AMQP的協議中規定有14個；而很多大部分我們沒有用到。常用的幾個屬性有：

English代碼  

Message properties
The AMQP protocol predefine a set of 14 properties that go with a message. Most of the properties are rarely used, with the exception of the following:

delivery_mode: Marks a message as persistent (with a value of 2) or transient (any other value). You may remember this property from the second tutorial. 
content_type: Used to describe the mime-type of the encoding. For example for the often used JSON encoding it is a good practice to set this property to: application/json. 
reply_to: Commonly used to name a callback queue. 
correlation_id: Useful to correlate RPC responses with requests. 

 delivery_mode : 標記消息是持久性消息還是瞬態信息。在前面的“Work Queue”中我們已經提到過；   

  content_type : 用來描述MIME的類型。如把其類型設定為JSON；

  reply_to : 用於命名一個回調Queue；

  correlation_id : 用於與相關聯的請求的RPC響應.

當客戶端想要調用服務器的某個方法來完成某項功能時，就可以使用rabbitMQ支持的PRC服務。

其實RPC服務與普通的收發消息的區別不大， RPC的過程其實就是  

客戶端向服務端定義好的Queue發送消息，其中攜帶的消息就應該是服務端將要調用的方法的參數 ，並使用Propertis告訴服務端將結果返回到指定的Queue。

示例：

package com.zf.rabbitmq07;

import java.io.IOException;

import com.rabbitmq.client.AMQP.BasicProperties;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.ConsumerCancelledException;
import com.rabbitmq.client.QueueingConsumer;
import com.rabbitmq.client.QueueingConsumer.Delivery;
import com.rabbitmq.client.ShutdownSignalException;

public class RPCServer {
    
    public static final String RPC_QUEUE_NAME = "rpc_queue";
    
    public static String sayHello(String name){
        return "hello " + name ;
    }
    
    public static void main(String[] args) throws IOException, ShutdownSignalException, ConsumerCancelledException, InterruptedException {
        
        ConnectionFactory connFac = new ConnectionFactory() ;
        connFac.setHost("localhost");
        
        Connection conn = connFac.newConnection() ;
        
        Channel channel = conn.createChannel() ;
        
        channel.queueDeclare(RPC_QUEUE_NAME, false, false, false, null) ;
        
        QueueingConsumer consumer = new QueueingConsumer(channel);
        
        channel.basicConsume(RPC_QUEUE_NAME, false , consumer) ;
        
        while(true){
            System.out.println("服務端等待接收消息..");  
            Delivery deliver = consumer.nextDelivery() ;
            System.out.println("服務端成功收到消息..");
            BasicProperties props =  deliver.getProperties() ;
            
            String message = new String(deliver.getBody() , "UTF-8") ;
            
            String responseMessage = sayHello(message) ;
            
            BasicProperties responseProps = new BasicProperties.Builder()
            .correlationId(props.getCorrelationId())  
            .build() ;
            
            //將結果返回到客戶端Queue
            channel.basicPublish("", props.getReplyTo() , responseProps , responseMessage.getBytes("UTF-8") ) ;
             
            //向客戶端確認消息
            channel.basicAck(deliver.getEnvelope().getDeliveryTag(), false);
            System.out.println("服務端返回消息完成..");
        }
        
    }

}

package com.zf.rabbitmq07;

import java.io.IOException;
import java.util.UUID;

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.ConsumerCancelledException;
import com.rabbitmq.client.QueueingConsumer;
import com.rabbitmq.client.AMQP.BasicProperties;
import com.rabbitmq.client.QueueingConsumer.Delivery;
import com.rabbitmq.client.ShutdownSignalException;

public class RPCClient {

    public static final String RPC_QUEUE_NAME = "rpc_queue";

    public static void main(String[] args) throws IOException, ShutdownSignalException, ConsumerCancelledException, InterruptedException {

        ConnectionFactory connFac = new ConnectionFactory() ;
        connFac.setHost("localhost");
        Connection conn = connFac.newConnection() ;
        Channel channel = conn.createChannel() ;

        //響應QueueName ，服務端將會把要返回的信息發送到該Queue
        String responseQueue = channel.queueDeclare().getQueue() ;

        String correlationId = UUID.randomUUID().toString() ;

        BasicProperties props = new BasicProperties.Builder()
        .replyTo(responseQueue)
        .correlationId(correlationId)
        .build();

        String message = "is_zhoufeng";
        channel.basicPublish( "" , RPC_QUEUE_NAME , props ,  message.getBytes("UTF-8"));

        QueueingConsumer consumer = new QueueingConsumer(channel)    ;

        channel.basicConsume( responseQueue , consumer) ;

        while(true){
            
            Delivery delivery = consumer.nextDelivery() ;
            
            if(delivery.getProperties().getCorrelationId().equals(correlationId)){
                String result = new String(delivery.getBody()) ;  
                System.out.println(result);
            }
            
        }
    }

}