Java for Web学习笔记（九四）：消息和集群（9）RabbitMQ和消息模式（下）

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例子：RPC的实现

这是一个通过AMQP使用RPC的例子，RPC是个同步的处理，需要等待响应。在实际应用需要特别消息，server可能性能很慢，server可能关闭。我们是否一定要使用RPC，是否可以用异步的方式替代。在此，我们只是演示如何利用RabbitMQ提供的消息管理来实现一个RPC。思路如下：

RPC Server从一个队列rpc_queue中接收消息，RPC client将请求消息发往rpc_queue队列。
消息的Properties中Correlation-Id带有这个请求的UUID，用于和响应对应。
消息的Properties中Reply-to带有client希望从那个队列中接收这个响应。
RPC的调用是同步的，通过BlockingQueue来实现这一个过程。

小例子将简单模拟Fibonacci函数

RPC Server的代码

public class FibonacciRPCServer {    private static final Logger log = LogManager.getLogger();    private static final String RPC_QUEUE_NAME = "rpc_queue";    private Connection connection = null;    private Channel channel = null;    public FibonacciRPCServer() throws IOException, TimeoutException{        ConnectionFactory factory = new ConnectionFactory();        factory.setHost("191.8.1.107");        factory.setUsername("test");        factory.setPassword("123456");                connection = factory.newConnection();        channel = connection.createChannel();    }    public void open() throws IOException {                    channel.queueDeclare(RPC_QUEUE_NAME, false, false, false, null);        channel.basicQos(1);        log.info(" [x] Awaiting RPC requests");        Consumer consumer = new DefaultConsumer(channel) {            @Override            public void handleDelivery(String consumerTag, Envelope envelope, BasicProperties properties, byte[] body)                    throws IOException {                try {                    BasicProperties replyProps = new BasicProperties.Builder()                            .correlationId(properties.getCorrelationId()).build();                    String message = new String(body,"UTF-8");                    int n = Integer.parseInt(message);                    log.info(" [.] fib(" + message + ")");                    String response = String.valueOf(fib(n));                    channel.basicPublish( "", properties.getReplyTo(), replyProps, response.getBytes("UTF-8"));                } finally {                    channel.basicAck(envelope.getDeliveryTag(), false);                }            }        };        channel.basicConsume(RPC_QUEUE_NAME, false, consumer); // 需要应答的        }    public void close(){                try {            if(channel != null)                channel.close();        } catch (IOException | TimeoutException e) {            e.printStackTrace();        }        try{            if(connection != null)                connection.close();        }catch (IOException e) {            e.printStackTrace();        }            }    private static int fib(int n) {        if (n ==0) return 0;        if (n == 1) return 1;        return fib(n-1) + fib(n-2);    }}

RPC Client的代码

public class FibonacciRPCClient {    private static final Logger log = LogManager.getLogger();    private Connection connection;    private Channel channel;    private String requestQueueName = "rpc_queue";    private String replyQueueName;    public FibonacciRPCClient() throws IOException, TimeoutException{        ConnectionFactory factory = new ConnectionFactory();        factory.setHost("191.8.1.107");        factory.setUsername("test");        factory.setPassword("123456");        connection = factory.newConnection();        channel = connection.createChannel();        replyQueueName = channel.queueDeclare().getQueue();    }    public String call(String message) throws UnsupportedEncodingException, IOException, InterruptedException{        String corrId = UUID.randomUUID().toString();        BasicProperties props = new BasicProperties.Builder()                .correlationId(corrId).replyTo(replyQueueName).build();        channel.basicPublish("", requestQueueName, props, message.getBytes("UTF-8"));        final BlockingQueue<String> response = new ArrayBlockingQueue<String>(1);        channel.basicConsume(replyQueueName, true, new DefaultConsumer(channel){            @Override            public void handleDelivery(String consumerTag, Envelope envelope, BasicProperties properties, byte[] body)                    throws IOException {                if (properties.getCorrelationId().equals(corrId)) {                    response.offer(new String(body, "UTF-8"));                }            }        });        return response.take();    }    public void close(){                // ... 略 ...关闭channel和connection    }}

上面，我们注意到

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

我们看一看抓包：

相关链接：我的Professional Java for Web Applications相关文章

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