java - 如何断开客户端与 NIO 服务器套接字的连接

Question

我正在开发一个与许多客户端相连的服务器。我需要知道客户端何时与服务器断开连接。所以每个客户端都向服务器发送一个特定的字符。如果两秒后没有收到字符，那么我应该断开服务器与客户端的连接(释放为此客户端分配的资源)。

这是我的服务器的主要代码:

public EchoServer(int port) throws IOException {
    this.port = port;
    hostAddress = InetAddress.getByName("127.0.0.1");
    selector = initSelector();
    loop();
}

private Selector initSelector() throws IOException {
    Selector socketSelector = SelectorProvider.provider().openSelector();

    ServerSocketChannel serverChannel = ServerSocketChannel.open();
    serverChannel.configureBlocking(false);

    InetSocketAddress isa = new InetSocketAddress(hostAddress, port);
    serverChannel.socket().bind(isa);
    serverChannel.register(socketSelector, SelectionKey.OP_ACCEPT);

    return socketSelector;
}

private void loop() {
    for (;true;) {
        try {
            selector.select();
            Iterator<SelectionKey> selectedKeys = selector.selectedKeys()
                    .iterator();
            while (selectedKeys.hasNext()) {
                SelectionKey key = selectedKeys.next();
                selectedKeys.remove();

                if (!key.isValid()) {
                    continue;
                }

                // Check what event is available and deal with it
                if (key.isAcceptable()) {
                    accept(key);
                } else if (key.isReadable()) {
                    read(key);
                } else if (key.isWritable()) {
                    write(key);
                }
            }
            Thread.sleep(1000);
            timestamp++;
        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }       
    }
}

第一个问题是，我用来识别在线客户端(每秒发送特定消息)的方法是否是一种好方法？

如果是好的，我如何检测 SelectionKey 是否与女巫客户端相关，然后如何断开与服务器的 key ？

Answer 1

The first question is that, whether the way that I used in order to recognizing online clients (sending specific message every second) is a good approach or not?

不是在回显服务器的情况下。在诸如此类的许多情况下，您所需要做的就是适本地识别流结束和连接失败。

how can I detect with SelectionKey is related to which client

SelectionKey有一个channel，channel有一个socket，Socket有一个remote IP address:port。这就是您所需要的。

and then how can I disconnect the key from server?

当您从 read() 方法或任何 IOException 读取或写入时获得 -1 时关闭 channel 。