如何在 Jetty 9 中访问实例化的 WebSocket？

Question

这可能很明显，但我对这种范式很陌生。我创建了一个 Jetty Server 并按如下方式注册了我的 websocket 类：

        Server server = new Server(8080);
        WebSocketHandler wsHandler = new WebSocketHandler()
        {
            @Override
            public void configure(WebSocketServletFactory factory)
            {
                factory.register(MyEchoSocket.class);
            }
        };
        server.setHandler(wsHandler);

websocket 接收消息正常。我还希望能够在没有先从客户端收到消息的情况下从服务器发送消息。如何访问连接打开时创建的 MyEchoSocket 实例？或者，更一般地说，如何在 MyEchoSocket 中的 onText 方法之外的套接字上发送消息？

Answer 1

两种常用技术，在此以超级简化的聊天室概念呈现。

选项 #1：让 WebSocket 将其状态报告回一个中心位置

@WebSocket
public class ChatSocket {
    public Session session;

    @OnWebSocketConnect
    public void onConnect(Session session) {
        this.session = session;
        ChatRoom.getInstance().join(this);
    }

    @OnWebSocketMessage
    public void onText(String message) {
        ChatRoom.getInstance().writeAllMembers("Hello all");
    }

    @OnWebSocketClose
    public void onClose(int statusCode, String reason) {
        ChatRoom.getInstance().part(this);
    }
}

public class ChatRoom {
    private static final ChatRoom INSTANCE = new ChatRoom();

    public static ChatRoom getInstance()
    {
        return INSTANCE;
    }

    private List<ChatSocket> members = new ArrayList<>();

    public void join(ChatSocket socket) 
    {
        members.add(socket);
    }

    public void part(ChatSocket socket) 
    {
        members.remove(socket);
    }

    public void writeAllMembers(String message) 
    {
        for(ChatSocket member: members)
        {
            member.session.getRemote().sendStringByFuture(message);
        }
    }

    public void writeSpecificMember(String memberName, String message) 
    {
        ChatSocket member = findMemberByName(memberName);
        member.session.getRemote().sendStringByFuture(message);
    }

    public ChatSocket findMemberByName(String memberName) 
    {
        // left as exercise to reader
    }
}

然后只需使用中心位置与您选择的 websocket 通信。

ChatRoom.getInstance().writeSpecificMember("alex", "Hello");

// or

ChatRoom.getInstance().writeAllMembers("Hello all");

选项 #2：使用 WebSocketCreator 手动创建 WebSocket

@WebSocket
public class ChatSocket {
    public ChatRoom chatroom;

    public ChatSocket(ChatRoom chatroom)
    {
        this.chatroom = chatroom;
    }

    @OnWebSocketConnect
    public void onConnect(Session session) {
        chatroom.join(this);
    }

    @OnWebSocketMessage
    public void onText(String message) {
        chatroom.writeAllMembers(message);
    }

    @OnWebSocketClose
    public void onClose(int statusCode, String reason) {
        chatroom.part(this);
    }
}

public class ChatCreator implements WebSocketCreator
{
    private ChatRoom chatroom;

    public ChatCreator(ChatRoom chatroom)
    {
        this.chatroom = chatroom;
    }

    public Object createWebSocket(UpgradeRequest request, 
                                  UpgradeResponse response)
    {
        // We want to create the Chat Socket and associate
        // it with our chatroom implementation
        return new ChatSocket(chatroom);
    }
}

public class ChatHandler extends WebSocketHandler
{
    private ChatRoom chatroom = new ChatRoom();

    @Override
    public void configure(WebSocketServletFactory factory)
    {
        factory.setCreator(new ChatCreator(chatroom));
    }
}

此时，您可以使用与上述相同的技术与您选择的 websocket 通信。