如何通过Web套接字向连接的用户发送消息? [英] How to send a message through web socket to a connected user?

问题描述

我想通过Web套接字向特定用户发送消息.到目前为止，我可以打开Web套接字并像这样从客户端读取消息:

I want to send a message through a web socket to a specific user. So far I can open a web socket and read message from client like that:

@ServerEndpoint(value = "/wsep")
public class WebSocketEndpoint {

    private static final Logger LOGGER = LoggerFactory.getLogger(WebSocketEndpoint.class);

    private Session session;

    @OnOpen
    public void onOpen(Session session) {
        this.session = session;
        try {
            session.getBasicRemote().sendText("You are connected. Your ID is " + session.getId());
        } catch (Exception e) {
            LOGGER.error("Error on open web socket", e);
        }
    }

    @OnMessage
    public void onClientMessage(String message, Session session) {      
        LOGGER.info("Message from {} is: {}", session.getId(), message);
    }

    @OnClose
    public void onClose(Session session) {
        this.session = null;
        LOGGER.info("{} disconnected", session.getId());
    }
}

我有一个独立的服务，可以在目标用户中创建消息.我的Message类是一个简单的POJO:

I have an independent service which creates message in destination to a user. My Message class is a simple POJO:

public class Message {
    private String fromUserName;
    private String toUserName;
    private String content;
    ...
}

在我的MessageService中创建新消息时，我想通知接收者是否已连接.我想我必须添加方法WebSocketEndpoint.onServerMessage:

When a new message is created in my MessageService, I want to inform the receiver if he is connected. I think I have to add a method WebSocketEndpoint.onServerMessage:

public void onServerMessage(Session session, Message message) {
    session.getBasicRemote().sendText(message.getContent());
}

但是我不知道该怎么做.

But I don't know how to do something like that which works.

推荐答案

所有用户都将有一个ServerEndpoint实例.因此，它应该存储所有客户端会话.正如Vu.N所建议的那样，一种方法是使用地图:

There will be one instance of the ServerEndpoint for all your users. So, it should store all client sessions. As Vu.N suggested, one way you can do it is using a map:

Map<String, Session> sessions = new ConcurrentHashMap<>();

public void onOpen(Session session) {
    String username = [...]
    sessions.put(username, session);
}

然后，很容易将消息发送给用户:

Then, it will be easy to send the message to the user:

public void onServerMessage(Session session, Message message) {
    sessions.get(message.getToUserName())
            .getBasicRemote() // see also getAsyncRemote()
            .sendText(message.getContent());
}

现在最难的部分是获取username吗?

Now the hardest part is to get the username?

在我过去的作品中，我通过3种方式来做到这一点:

In my past works, I've done it in 3 ways:

1. 客户端连接到具有某些密钥"的URL.此密钥"将用于查找正确的用户名. WebSocket服务器端点将是这样的:

1. The client connects to a URL that has some "key". This "key" would be used to find the right username. The WebSocket server endpoint would be like this:

@ServerEndpoint(value="/wsep/{key}") // the URL will have an extra "key"
public class WebSocketEndpoint {
[...]
@OnOpen
public void onOpen(Session session, @PathParam("key") String key) {
    String username = getUserNameWithKey(key);
    sessions.add(username, session);
}

客户端在第一条消息中发送一些信息.您只需忽略@OnOpen部分:

The client sends some information in the first message. You just ignore the @OnOpen part:

@OnOpen
public void onOpen(Session session) {
    LOGGER.info("Session open. ID: {}", session.getId());
}

@OnMessage
public void onMessage(Session session, String message) {
    String username = getUserNameFromMessage(message);
    sessions.add(username, session);
}

某些用户信息可以从Cookie，JWT或其他内容获得.您需要ServerEndpointConfig.Configurator才能从请求中获取该信息.例如:

Some user info can be obtained from a cookie, JWT, or something. You'll need a ServerEndpointConfig.Configurator to get that information from the request. For example:

public class CookieServerConfigurator extends ServerEndpointConfig.Configurator {

    @Override
    public void modifyHandshake(ServerEndpointConfig sec, HandshakeRequest request, HandshakeResponse response) {
        Map<String,List<String>> headers = request.getHeaders();
        sec.getUserProperties().put("cookie", headers.get("cookie"));
    }
}

然后，服务器端点将指向该配置程序:

Then, the server endpoint will point to that configurator:

@ServerEndpoint(value = "/example2/", configurator = CookieServerConfigurator.class)
public class WebSocketEndpoint {

您将获得如下信息:

@OnOpen
public void onOpen(Session session, EndpointConfig endpointConfig) {
    String username = getUsername((List<String>)endpointConfig.getUserProperties().get("cookie"));

您可以在此处看到一些有效的示例: https://github.com/matruskan/websocket-example

You can see some working examples here: https://github.com/matruskan/websocket-example

对于更复杂的系统，您也可以使用标记系统"，而不是使用Map.然后，每个会话都可以接收发送到其任何标签的消息，并且发送到标签的消息可以定向到许多会话.

For more complex systems, you can also have a "tagging system", instead of using a Map. Then, each session can receive messages sent to any of its tags, and a message sent to a tag can be directed to many sessions.

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