RabbitMQ学习笔记：实现简单的RPC功能

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环境

window10
虚拟机、secureCRT
Intellij IDEA

RPC

Remote Procedure Call。

远程过程调用：调用的程序或者函数，并不在本地，而是在远程计算机中。这个时候不能直接调用，需要通过网络来表达调用的语义和传达调用的数据。

要利用RabbitMQ来实现RPC功能是很简单的；客户端发送消息，服务端回复响应的消息。为了接收响应的消息，我们需要在请求中发送一个回调队列。可以使用默认的队列。

String message = "rabbitmq rpc";
// 匿名回调队列
String callbackQueueName = channel.queueDeclare().getQueue();
// 设置回调队列
AMQP.BasicProperties props = 
new AMQP.BasicProperties.Builder().replyTo(callbackQueueName).build();
channel.basicPublish("", "rpc_queue", props, message.getBytes());

流程图：
在这里插入图片描述

步骤

① 客户端创建一个匿名队列作为回调队列。
② 客户端为RPC请求设置2个属性：replayTo用来告知RPC服务端回复请求时的目的队列（也就是上面的匿名队列）即回调队列；。correlationId用来标记请求的唯一性。
③ 请求发送到rpc_queue队列中。
④ RPC服务端监听rpc_queue队列中的请求，当请求来到时，服务端会处理并且把带有结果的消息发送给客户端。接收的队列就是replyTo设定的回调队列。
⑤ 客户端监听回调队列，当有消息时，检查correlationId属性，如果与请求匹配，那就是结果了。

这里贴出官网的代码：

server端：

import com.rabbitmq.client.*;public class RPCServer {private static final String RPC_QUEUE_NAME = "rpc_queue";private static int fib(int n) {if (n == 0) return 0;if (n == 1) return 1;return fib(n - 1) + fib(n - 2);}public static void main(String[] argv) throws Exception {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");try (Connection connection = factory.newConnection();Channel channel = connection.createChannel()) {// 声明一个队列channel.queueDeclare(RPC_QUEUE_NAME, false, false, false, null);// 清空队列里的内容channel.queuePurge(RPC_QUEUE_NAME);// 设置客户端最多接收未被确认ack的消息的个数channel.basicQos(1);System.out.println(" [x] Awaiting RPC requests");Object monitor = new Object();DeliverCallback deliverCallback = (consumerTag, delivery) -> {AMQP.BasicProperties replyProps = new AMQP.BasicProperties.Builder().correlationId(delivery.getProperties().getCorrelationId()).build();String response = "";try {String message = new String(delivery.getBody(), "UTF-8");int n = Integer.parseInt(message);System.out.println(" [.] fib(" + message + ")");response += fib(n);} catch (RuntimeException e) {System.out.println(" [.] " + e.toString());} finally {channel.basicPublish("", delivery.getProperties().getReplyTo(), replyProps, response.getBytes("UTF-8"));channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);// RabbitMq consumer worker thread notifies the RPC server owner threadsynchronized (monitor) {monitor.notify();}}};channel.basicConsume(RPC_QUEUE_NAME, false, deliverCallback, (consumerTag -> { }));// Wait and be prepared to consume the message from RPC client.while (true) {synchronized (monitor) {try {monitor.wait();} catch (InterruptedException e) {e.printStackTrace();}}}}}
}

client端：

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;import java.io.IOException;
import java.util.UUID;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeoutException;public class RPCClient implements AutoCloseable {private Connection connection;private Channel channel;private String requestQueueName = "rpc_queue";public RPCClient() throws IOException, TimeoutException {ConnectionFactory factory = new ConnectionFactory();factory.setHost("localhost");connection = factory.newConnection();channel = connection.createChannel();}public static void main(String[] argv) {try (RPCClient fibonacciRpc = new RPCClient()) {for (int i = 0; i < 32; i++) {String i_str = Integer.toString(i);System.out.println(" [x] Requesting fib(" + i_str + ")");String response = fibonacciRpc.call(i_str);System.out.println(" [.] Got '" + response + "'");}} catch (IOException | TimeoutException | InterruptedException e) {e.printStackTrace();}}public String call(String message) throws IOException, InterruptedException {final String corrId = UUID.randomUUID().toString();String replyQueueName = channel.queueDeclare().getQueue();AMQP.BasicProperties props = new AMQP.BasicProperties.Builder().correlationId(corrId).replyTo(replyQueueName).build();// 空字符就是使用默认交换器 direct类型的。// 这个默认交换器有个特性：// 每个队列都会自动和这个默认交换器进行绑定，绑定的路由键就是队列名// 这个是rabbitmq自动完成的。// 这也就可以解释：我们没有将回调队列和默认交换器进行绑定，// 但是下面这段代码却可以将消息发送出去。channel.basicPublish("", requestQueueName, props, message.getBytes("UTF-8"));final BlockingQueue<String> response = new ArrayBlockingQueue<>(1);// 监听匿名队列，消费消息String ctag = channel.basicConsume(replyQueueName, true, (consumerTag, delivery) -> {if (delivery.getProperties().getCorrelationId().equals(corrId)) {response.offer(new String(delivery.getBody(), "UTF-8"));}}, consumerTag -> {});String result = response.take();// 取消订阅channel.basicCancel(ctag);return result;}public void close() throws IOException {connection.close();}
}