Question

我希望在SocketChannel调用close方法时收到通知。我的第一个想法是创建一个包装器，在调用implCloseSelectableChannel方法时通知监听器（因为close方法本身在final中声明为AbstractInterruptibleChannel）。此解决方案有效，但当我尝试使用Selector进行注册时，由于IllegalSelectorException中的以下检查，我将获得SelectorImpl：

/*     */   protected final SelectionKey register(AbstractSelectableChannel paramAbstractSelectableChannel, int paramInt, Object paramObject)
/*     */   {
/* 128 */     if (!(paramAbstractSelectableChannel instanceof SelChImpl))
/* 129 */       throw new IllegalSelectorException();

现在我无法覆盖register方法以委托给包裹的SocketChannel，因为它在final中声明为AbstractSelectableChannel而我无法实现SelChImpl因为它在sun.nio.ch包中具有默认可见性。我可以看到从这里开始的唯一方法是制作我自己的SelectorProvider和Selector，但这似乎有点过于简单。

关闭SocketChannel或者我是否需要重新考虑我的程序设计时，是否有更简单的方式获得通知？

SocketChannelWrapper示例：

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.net.SocketOption;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;

public class SocketChannelWrapper extends SocketChannel {
    private static interface CloseListener {
        public void socketChannelClosed(SocketChannel channel);
    }

    private final SocketChannel socket;
    private final CloseListener listener;

    public SocketChannelWrapper(SocketChannel socket, CloseListener l) {
        super(socket.provider());
        this.socket = socket;
        listener = l;
    }

    @Override
    public SocketAddress getLocalAddress() throws IOException {
        return socket.getLocalAddress();
    }

    @Override
    public <T> T getOption(SocketOption<T> name) throws IOException {
        return socket.getOption(name);
    }

    @Override
    public Set<SocketOption<?>> supportedOptions() {
        return socket.supportedOptions();
    }

    @Override
    public SocketChannel bind(SocketAddress local) throws IOException {
        return socket.bind(local);
    }

    @Override
    public <T> SocketChannel setOption(SocketOption<T> name, T value)
            throws IOException {
        return socket.setOption(name, value);
    }

    @Override
    public SocketChannel shutdownInput() throws IOException {
        return socket.shutdownInput();
    }

    @Override
    public SocketChannel shutdownOutput() throws IOException {
        return socket.shutdownOutput();
    }

    @Override
    public Socket socket() {
        return socket.socket();
    }

    @Override
    public boolean isConnected() {
        return socket.isConnected();
    }

    @Override
    public boolean isConnectionPending() {
        return socket.isConnectionPending();
    }

    @Override
    public boolean connect(SocketAddress remote) throws IOException {
        return socket.connect(remote);
    }

    @Override
    public boolean finishConnect() throws IOException {
        return socket.finishConnect();
    }

    @Override
    public SocketAddress getRemoteAddress() throws IOException {
        return socket.getRemoteAddress();
    }

    @Override
    public int read(ByteBuffer dst) throws IOException {
        return socket.read(dst);
    }

    @Override
    public long read(ByteBuffer[] dsts, int offset, int length)
            throws IOException {
        return socket.read(dsts, offset, length);
    }

    @Override
    public int write(ByteBuffer src) throws IOException {
        return socket.write(src);
    }

    @Override
    public long write(ByteBuffer[] srcs, int offset, int length)
            throws IOException {
        return socket.write(srcs, offset, length);
    }

    @Override
    protected void implCloseSelectableChannel() throws IOException {
        socket.close();
        listener.socketChannelClosed(this);
    }

    @Override
    protected void implConfigureBlocking(boolean block) throws IOException {
        socket.configureBlocking(block);
    }

    public static void main(String[] args) throws UnknownHostException,
            IOException {
        final Selector selector = Selector.open();
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        selector.select();
                        Iterator<SelectionKey> itr = selector.selectedKeys()
                                .iterator();
                        while (itr.hasNext()) {
                            SelectionKey key = itr.next();
                            itr.remove();

                            if (key.isValid()) {
                                if (key.isAcceptable()) {
                                    ((ServerSocketChannel) key.channel())
                                            .accept();
                                }
                            }
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
        t.setDaemon(true);

        ServerSocketChannel server = ServerSocketChannel.open().bind(
                new InetSocketAddress(1234));
        server.configureBlocking(false);

        server.register(selector, SelectionKey.OP_ACCEPT);
        t.start();

        SocketChannel socket = new SocketChannelWrapper(
                SocketChannel.open(new InetSocketAddress(InetAddress
                        .getLocalHost(), 1234)), new CloseListener() {
                    @Override
                    public void socketChannelClosed(SocketChannel channel) {
                        System.out.println("Socket closed!");
                    }
                });
        socket.configureBlocking(false);
        // socket.close(); //prints out "Socket closed!"
        socket.register(selector, SelectionKey.OP_READ);
    }
}

Answer 1

如果SocketChannel已被您关闭，您正在关闭它，因此您可以按照自己喜欢的方式通知自己。

如果您希望在 peer 关闭连接时收到通知，OP_READ将会触发，读取将返回-1。

Answer 2

那是令人讨厌的。您可以使用像http://www.csg.ci.i.u-tokyo.ac.jp/~chiba/javassist/这样的字节级aop包（使用aop，你可以在close方法上添加一个cutpoint来进行回调）。

您还可以创建一个与sun包同名的包，并在那里实现接口。

但是我看不到一个好的，干净的方法来做到这一点。

如何在SocketChannel关闭时收到通知？

2 个答案: