rabbitmq学习6:RPC

在《rabbitmq学习2:Work Queues 》中我们已经知道了在多个worker如何分配耗时的任务。如果我现在要在远程的机器上运行然后得到结果，那应当怎么做呢？那就要用到RPC（Remote Procedure Call or RPC ）了！

   关于RPC的介绍请参考百度百科里的关于RPC的介绍：http://baike.baidu.com/view/32726.htm#sub32726

   现在来看看来看看Rabbitmq中RPC吧！RPC的工作示意图如下：

   上图中的C代表客户端，S表示服务器端；Rabbitmq中的RPC流程如下：

1、首先客户端发送一个reply_to和corrention_id的请求,发布到RPC队列中；

2、服务器端处理这个请求，并把处理结果发布到一个回调Queue,此Queue的名称应当与reply_to的名称一致

3、客户端从回调Queue中得到先前corrention_id设定的值的处理结果。如果碰到和先前不一样的corrention_id的值，将会忽略而不是抛出异常。

 

  对于上面所提到的回调Queue中的消费处理使用的是BasicProperties类；而消息 属性在AMQP的协议中规定有14个；而很多大部分我们没有用到。常用的几个属性有：

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 : 标记消息是持久性消息还是瞬态信息。在前面的“Work Queue”中我们已经提到过；   

  content_type : 用来描述MIME的类型。如把其类型设定为JSON；

  reply_to : 用于命名一个回调Queue；

  correlation_id : 用于与相关联的请求的RPC响应.

  现在我们就开始RPC的程序吧！

client的代码如下：

package com.abin.rabbitmq;

import java.util.UUID;

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.QueueingConsumer;

public class RPCClient {
    private Connection connection;
    private Channel channel;
    private String requestQueueName = "rpc_queue";
    private String replyQueueName;
    private QueueingConsumer consumer;

    public RPCClient() throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");
        connection = factory.newConnection();
        channel = connection.createChannel();

        replyQueueName = channel.queueDeclare().getQueue();
        consumer = new QueueingConsumer(channel);
        channel.basicConsume(replyQueueName, true, consumer);
    }

    public String call(String message) throws Exception {
        String response = null;
        String corrId = UUID.randomUUID().toString();

        BasicProperties props = new BasicProperties();
        props.setReplyTo(replyQueueName);
        props.setCorrelationId(corrId);

        channel.basicPublish("", requestQueueName, props, message.getBytes());

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

        return response;
    }

    public void close() throws Exception {
        connection.close();
    }

    public static void main(String[] argv) {
        RPCClient fibonacciRpc = null;
        String response = null;
        try {
            fibonacciRpc = new RPCClient();

            System.out.println(" [x] Requesting fib(30)");
            response = fibonacciRpc.call("30");
            System.out.println(" [.] Got '" + response + "'");
            System.out.println(" [x] Requesting fib(-1)");
            response = fibonacciRpc.call("-1");
            System.out.println(" [.] Got '" + response + "'");
            System.out.println(" [x] Requesting fib(a)");
            response = fibonacciRpc.call("a");
            System.out.println(" [.] Got '" + response + "'");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fibonacciRpc != null) {
                try {
                    fibonacciRpc.close();
                } catch (Exception ignore) {
                }
            }
        }
    }
}

 

 server的代码如下：

package com.abin.rabbitmq;

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.QueueingConsumer;

public class RPCServer {
    private static final String RPC_QUEUE_NAME = "rpc_queue";

    private static int fib(int n) {
        if (n > 1)
            return fib(n - 1) + fib(n - 2);
        else
            return n;
    }

    public static void main(String[] argv) {
        Connection connection = null;
        Channel channel = null;
        try {
            ConnectionFactory factory = new ConnectionFactory();
            factory.setHost("localhost");

            connection = factory.newConnection();
            channel = connection.createChannel();

            channel.queueDeclare(RPC_QUEUE_NAME, false, false, false, null);

            channel.basicQos(1);

            QueueingConsumer consumer = new QueueingConsumer(channel);
            channel.basicConsume(RPC_QUEUE_NAME, false, consumer);

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

            while (true) {
                String response = null;

                QueueingConsumer.Delivery delivery = consumer.nextDelivery();

                BasicProperties props = delivery.getProperties();
                BasicProperties replyProps = new BasicProperties();
                replyProps.setCorrelationId(props.getCorrelationId());

                try {
                    String message = new String(delivery.getBody(), "UTF-8");
                    int n = Integer.parseInt(message);

                    System.out.println(" [.] fib(" + message + ")");
                    response = "" + fib(n);
                } catch (Exception e) {
                    System.out.println(" [.] " + e.toString());
                    response = "";
                } finally {
                    channel.basicPublish("", props.getReplyTo(), replyProps,
                            response.getBytes("UTF-8"));

                    channel.basicAck(delivery.getEnvelope().getDeliveryTag(),
                            false);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (connection != null) {
                try {
                    connection.close();
                } catch (Exception ignore) {
                }
            }
        }
    }
}

 

先运行服务器端，运行结果如下：

[x] Awaiting RPC requests

   再运行运行客户端，运行结果如下：

[x] Requesting fib(30)
[.] Got '832040'
[x] Requesting fib(-1)
[.] Got '-1'
[x] Requesting fib(a)
[.] Got ''

   在服务器还可以出现：

[.] fib(30)
[.] fib(-1)
[.] java.lang.NumberFormatException: For input string: "a"

 

 

 

•