我以前有Kafka的知识，并且一直在与Nats.io一起玩，这似乎是消息传递的可靠选择。
特别是，我对文档齐全的请求/回复机制感兴趣，但是我很难用Jnats驱动程序在Java中正确实现它。
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);
}
}
这是请求方法（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Response Handler：
@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");
}
}
});
}
我的两个独立服务通过docker化的Nats.io进行通信，我可以通过Nats Go客户端正确检查两个服务是否已在同一主题上发送了消息。
不幸的是，即使在
asyncRequest中等待量很高时，“请求者”在调用reply.get(...)函数时也无法完全处理答复。当我尝试在调试模式下评估
reply对象时，该对象中没有任何数据，并显示了TimeoutException。在
msg.getData()处，程序崩溃。你们对我有什么提示吗？
谢谢！
最佳答案
您应该更改“回复”代码以从原始消息发布到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");
}
}
});
}
请求回复机制正在针对生成的replyTo主题寻找单个响应。
见https://docs.nats.io/nats-concepts/reqreply