Java中的Nats请求/应答

g6ll5ycj  于 2023-09-29  发布在  Java
关注(0)|答案(1)|浏览(108)

我以前有Kafka的知识,我一直在玩Nats.io,这似乎是一个非常可靠的消息传递选择。
特别是,我对文档完备的请求/应答机制很感兴趣,但在Java中使用Jnats驱动程序正确实现它时遇到了困难。
这是我的连接器:

// Single server nats connection
    @PostConstruct
    public void connect() throws ExternalServiceUnavailableException {

        Options options = new Options.Builder()
                .server(connectionString)
                .maxReconnects(20)
                .reconnectWait(Duration.ofSeconds(5))
                .connectionTimeout(Duration.ofSeconds(5))
                .connectionListener((conn, type) -> {
                    if (type == ConnectionListener.Events.CONNECTED) {
                        LOG.info("Connected to Nats Server");
                    } else if (type == ConnectionListener.Events.RECONNECTED) {
                        LOG.info("Reconnected to Nats Server");
                    } else if (type == ConnectionListener.Events.DISCONNECTED) {
                        LOG.error("Disconnected to Nats Server, reconnect attempt in seconds");
                    } else if (type == ConnectionListener.Events.CLOSED) {
                        LOG.info("Closed connection with Nats Server");
                    }
                })
                .build();

        try {
            connection = Nats.connect(options);

        } catch (Exception e) {
            LOG.error("Unable to connect to Nats Server");
            throw new ExternalServiceUnavailableException(ExternalServiceUnavailableException.Service.NATS);
        }

    }

这是request方法(出于测试目的,等待时间非常长):

public Optional<String> asyncRequest(String topic, String message) throws ExternalServiceUnavailableException {

        Future<Message> reply = natsConnector.getConnection().request(topic, message.getBytes());
        try {

            Message msg = reply.get(10L, TimeUnit.SECONDS);

            LOG.info(new String(msg.getData()));

            return Optional.of(new String(msg.getData(), StandardCharsets.UTF_8));

        } catch (InterruptedException | ExecutionException | TimeoutException e) {
            e.printStackTrace();
            LOG.error("Unable to retrieve response for the sent request: " + message);
            throw new ExternalServiceUnavailableException(ExternalServiceUnavailableException.Service.NATS);
        }

    }

这是带有回复机制的响应处理程序:

@PostConstruct
    private void init() {
        Dispatcher dispatcher = natsConnector.getConnection().createDispatcher(message -> {
        });

        Subscription assetsInfo = dispatcher.subscribe("assets-info", message -> {
        JSONObject requestMessage = new JSONObject(new String(message.getData(), StandardCharsets.UTF_8));

            if (requestMessage.getString("requestType").equals("stock-status")) {

                if (requestMessage.getString("of").equals("all")) {

                    JSONObject response = assetQuery.retrieveYesterdayStockStatus();
                    LOG.info("response ready");
                    natsOperation.publishEvent("assets-info", response);
                    LOG.info("message sent");
                }
            }
        });
    }

我的两个独立的服务通过dockerized Nats.io进行通信,我可以通过Nats Go客户端正确地检查两个服务是否发送了相同主题的消息。
不幸的是,当调用asyncRequest函数时,即使在reply.get(...)中有很高的await,“request”也不能完全处理回复。
当我尝试在调试模式下计算reply对象时,它没有任何数据,并显示TimeoutException
msg.getData()处,程序崩溃。
你们有什么提示吗谢谢你,谢谢

drkbr07n

drkbr07n1#

您应该更改您的“replyer”代码,以便从原始邮件发布到replyTo主题。

@PostConstruct
private void init() {
    Dispatcher dispatcher = natsConnector.getConnection().createDispatcher(message -> {});

    Subscription assetsInfo = dispatcher.subscribe("assets-info", message -> {
        JSONObject requestMessage = new JSONObject(
            new String(message.getData(), StandardCharsets.UTF_8)
        );

        if (requestMessage.getString("requestType").equals("stock-status")) {
            if (requestMessage.getString("of").equals("all")) {
                JSONObject response = assetQuery.retrieveYesterdayStockStatus();
                LOG.info("response ready");
                //See Change Here
                natsOperation.publish(message.getReplyTo(), response);
                LOG.info("message sent");
            }
        }
    });
}

请求应答机制在生成的replyTo主题上寻找单个响应。
参见https://docs.nats.io/nats-concepts/reqreply

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