如何在 Jetty 9 中访问实例化的 WebSocket？

这可能是显而易见的，但我对这种范例很陌生。我创建一个 Jetty 服务器并注册我的 websocket 类，如下所示：

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

Websocket 可以正常接收消息。我还希望能够从服务器发送消息，而无需先从客户端接收消息。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 onText 方法之外的套接字上发送消息？

此处以超级简化的聊天室概念介绍了两种常见技术。

选项#1：让 WebSocket 将其状态报告回中央位置

@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即可与您选择的 Websockets 进行通信。

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来与您选择的 Websocket 进行通信。