Netty - 如何在客户端获得服务器响应 [英] Netty - How to get server response in the client

问题描述

我主要是在那里与Netty，但一个概念仍然暗示我，我在教程中找不到任何东西，等等。首先我明白Netty是异步的，但是客户端必须有一种方法来调用服务器，并且能够在处理程序之外获得响应。让我解释更多。

I'm mostly there with Netty but one concept is still alluding me, and I can't find anything in the tutorials and so on. Firstly I do understand that Netty is asynchronous, but there must be a way for a client to call the server and be able to get a response beyond the handler. Let me explain more.

我有一个客户如下图所示。请注意，我理解它是自举的，每次调用都建立了一个新的连接，这只是为了使示例更小，更简洁。请忽略该事实。

I have a client as illustrated below. And please note that I understand it's bootstrapped and a new connection is established on each call, that's just there to make the example smaller and more succinct. Please ignore that fact.

Client.java

Client.java

// ServerResponse is a result from the server, in this case 
// a list of users of the system (ignore that each time it's all bootstrapped).

public User[] callServerForInformationFromGUIWidget()
{
    ClientBootstrap bootstrap = new ClientBootstrap(...);
    bootstrap.setPipelineFactory(...);

    ChannelFuture future = bootstrap.connect(new InetSocketAddress(host, port));
    Channel channel = future.awaitUninterruptibly().getChannel();

    // Where request is a POJO sent to the server, 
    // with a request such as get me a list of users
    RequestPojo request = new RequestPojo(requestUserListCommand);

    ChannelFuture lastWriteFuture = channel.write(request);

    if(lastWriteFuture != null)
        lastWriteFuture.awaitUninterruptibly();
}

现在我明白了如何获取服务器上的数据，结果。唯一的是如何在客户端处理它？是的，clientHandler类可以执行如下操作：

Now I understand how to get the data on the server, and fire back the result. The only thing is how do I handle it on the client side? Yes the clientHandler class can do something like the following:

ClientHandler.java

ClientHandler.java

@Override
public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) 
{
    User[] users = (User[])e.getMessage();
}

问题是客户端代码如何获得结果？所有示例都类似于聊天服务，其中事件触发了客户端上不等待响应的其他事情。甚至http客户端示例，我发现缺乏这一点。文档总体上是很好，但它缺乏如何做回调。无论如何，在这种情况下，我需要客户端从服务器获取响应，并基于结果，它会做它需要的。

The problem is how does the client code actually get that result? All the examples are similar to a chat service, where the event fires off something else on the client that's not waiting on a response. Even the http client example I found lacking this. The documentation overall is really good, but it's lacking on how to do callbacks. Anyways, in this case I need the client to get the response from the server, and based on the results it will do what it needs.

换句话说，我如何写客户端来做这样的事情：

In other words, how do I write the client to do something like this:

IdealClient.java

IdealClient.java

// ServerResponse is a result from the server, in this case 
// a list of users of the system.

public User[] callServerForInformationFromGUIWidget()
{
    ...
    RequestPojo request = new RequestPojo(requestUserListCommand);
    ChannelFuture lastWriteFuture = channel.write(request);

    if(lastWriteFuture != null)
        lastWriteFuture.awaitUninterruptibly();

    User[] users = resultFromCallToServer();

    performSomeAction(users);
}

因为处理程序不知道是谁在寻找答案，问的问题。如果它是在处理程序，而不是如何做？

Because the handler doesn't know who is looking for the answer, or who asked the question. And if it's done in the handler, than how?

回到我对示例的评论，http客户端（和处理程序）示例只是将结果转储到System.out。如果你有一个GUI，你如何将结果从你的请求传递到GUI？我从来没有看到任何例子。

Back to my comments about the examples, the http client (and handler) examples just dump the result to System.out. If you had a GUI how would you pass the result from your request up to the GUI? I never saw any examples for this.

推荐答案

Jestan是正确的。在我的情况下，我有一个客户端需要处理价格tick数据。我使用Antlr进行解析。我在我的解析器中触发我的事件，但在我的case我的协议是基于字符串。下面是一个没有Antlr的例子，我传递String消息在你的情况下它可以是用户。

Jestan is correct. In my case I have a client that need to process price tick data. I use Antlr for the parsing. I fire my events in my parser, but in my case my protocol is String based. Below is an example without Antlr, I pass the String message in your case it could be the users.

//----------------- Event --------------
public class DataChangeEvent {
    private String message;

    public DataChangeEvent(String message) {
        this.message = message;
    }

    public String getMessage() {
        return message;
    }


}

//----------------- Listener --------------
public interface DataChangeListenter {
    public void dataChangeEvent(DataChangeEvent event);
}

//----------------- Event Handler that fires the dataChange events --------------
// This class needs to be static since you need to register all your classes that want to be notified of data change events
public class DataChangedHandler {
    private static List<DataChangeListenter> listeners = new ArrayList<DataChangeListenter>();

    public static void registerDataChangeListener(DataChangeListenter listener) {
        listeners.add(listener);
    }

    public static void fireDataChange(DataChangeEvent dataChangeEvent) {
        for(DataChangeListenter listenter : listeners) {
            listenter.dataChangeEvent(dataChangeEvent);
        }
    }
}

//----------------- Example class that implements the listener and registers itself for events --------------
public class ProcessMessage implements DataChangeListenter {

    public ProcessMessage() {
        DataChangedHandler.registerDataChangeListener(this);
    }

    public void dataChangeEvent(DataChangeEvent event) {
        //Depending on your protocal, I use Antlr to parse my message
        System.out.println(event.getMessage());
    }


}

//---------------- Netty Handler -----------
public class TelnetClientHandler extends SimpleChannelHandler {

    private static final Logger logger = Logger.getLogger(TelnetClientHandler.class.getName());

    @Override
    public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
        String message = (String) e.getMessage();
        DataChangedHandler.fireDataChange(message);
    }
}

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