java - 当没有传入连接时 SelectionKey.isAcceptable() 返回 "true"

Question

我正在使用 Java NIO 用 Ja​​va 编写一个聊天服务器。服务器毫无问题地接受连接，但任何时候 select() 在第一个客户端之后返回 > 0 时，服务器套接字始终位于选定的键集中，即使没有挂起的连接也是如此。即使 select() 返回 1，选定的键集也将有 2 个元素并包括服务器套接字。这会导致accept()返回null。

任何帮助将不胜感激。

主循环:

public void start() throws IOException {
    Set<SelectionKey>       keys;
    Iterator<SelectionKey>  keyIterator;
    this.keepGoing = true;

    while (keepGoing) {
        int readyChannels = this.selector.select();

        if (readyChannels == 0) 
        {
            continue;
        }

        keys        = this.selector.selectedKeys();
        keyIterator = keys.iterator();

        while (keyIterator.hasNext())
        {
            SelectionKey currentKey = keyIterator.next();

            if (currentKey.isAcceptable())
            {
                addClient(currentKey);
            }
            if (currentKey.isReadable())
            {
                readSock(currentKey);
            }
            if (currentKey.isWritable())
            {
                // write data to the buffer and remove OP_WRITE
            }
        }
    }

}

服务器初始化代码:

public Server(int port) {

    this.listenPort = port;

    try
    {
        this.selector = Selector.open();
        this.listenChannel = ServerSocketChannel.open();
        this.listenChannel.socket().bind(new InetSocketAddress(this.listenPort), BACKLOG);
        this.listenChannel.configureBlocking(false);
        this.listenChannel.register(this.selector, SelectionKey.OP_ACCEPT);
    } 
    catch (IOException e)
    {
        System.out.println("Server could not initialise: " + e.getMessage());
    }

    this.users = new HashMap<>();
}

addClient 方法:

private void addClient(SelectionKey key) throws IOException {
    ServerSocketChannel acceptSocket    = (ServerSocketChannel) key.channel();
    SocketChannel       newClient       = acceptSocket.accept();
    SelectionKey        clientKey;

    // Set the new client to non-blocking mode and add to the selector
    newClient.configureBlocking(false);
    clientKey = newClient.register(this.selector, SelectionKey.OP_READ);

    // Add a new key-user pair to the user list
    this.users.put(clientKey, new User());

    // Attach a buffer for reading the packets
    clientKey.attach(new PacketBuffer(newClient));
}

Answer 1

您必须在 keyIterator.next() 之后调用 keyIterator.remove()，或者在循环结束时清除选定的键集。选择器不会从该集中删除键，这取决于您。但您还需要注意，accept() 在非阻塞模式下可以返回 null，并相应地进行防御性编程。