Question

我正在尝试设置套接字的SO_KEEPALIVE时间。

我创建了一个类SocketBuilder来使用SocketImpl构建套接字实例。源代码如下，

public class SocketBuilder {

    private static SocketImpl si;

    public static Socket createCVPSocket() throws Exception {
        if (si == null) {
            init();
        }
        return new CSocket(si);
    }    


    private static void init() throws SocketException {
        @SuppressWarnings("rawtypes")
        Constructor cons = null;
        try {
            cons = Class.forName("java.net.SocksSocketImpl")
                    .getDeclaredConstructor();
        } catch (NoSuchMethodException | SecurityException
                | ClassNotFoundException e) {
            throw new RuntimeException(
                    "Not able to access socket implementation.");
        }
        cons.setAccessible(true);
        SocketImpl si = null;
        try {
            si = (SocketImpl) cons.newInstance();
        } catch (InstantiationException | IllegalAccessException
                | IllegalArgumentException | InvocationTargetException e) {
            throw new RuntimeException("Not able to create instance of socket.");
        }
        if (si != null) {
            si.setOption(SocketImpl.SO_KEEPALIVE, new Integer(60));
        }
    }

    private static class CSocket extends Socket {
        protected CSocket(SocketImpl si) throws SocketException, Exception {
            super(si);
        }
    }
    public static void main(String[] args) {
        try {
            Socket sock = SocketBuilder.createCVPSocket();
            System.out.println(sock);
        } catch (Exception e) { 
            e.printStackTrace();
        }
    }
}

我收到java.net.SocketException: Socket Closed例外。如果我删除行si.setOption(SocketImpl.SO_KEEPALIVE, new Integer(60));，它可以正常工作。但我想设置SocketImpl.SO_KEEPALIVE。如何设置套接字SO_KEEPALIVE？

Answer 1

您的代码中存在一些错误：

SocketImpl si = null;此声明与您的课程字段重叠
setOption仅在套接字打开/连接

完成后必须关闭套接字

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.net.*;

public class SocketBuilder {
private static SocketImpl si;

public static Socket createCVPSocket() throws Exception {
    if (si == null) {
        init();
    }
    return new CSocket(si);
}    


private static void init() throws SocketException {
    @SuppressWarnings("rawtypes")
    Constructor cons = null;
    try {
        cons = Class.forName("java.net.SocksSocketImpl")
                .getDeclaredConstructor();
    } catch (NoSuchMethodException | SecurityException
            | ClassNotFoundException e) {
        throw new RuntimeException(
                "Not able to access socket implementation.");
    }
    cons.setAccessible(true);
    si = null;
    try {
        si = (SocketImpl) cons.newInstance();
    } catch (InstantiationException | IllegalAccessException
            | IllegalArgumentException | InvocationTargetException e) {
        throw new RuntimeException("Not able to create instance of socket.");
    }

}

private static class CSocket extends Socket {
    protected CSocket(SocketImpl si) throws SocketException, Exception {
        super(si);
        super.bind(new InetSocketAddress("127.0.0.1", 8888));

        si.setOption(SocketImpl.SO_KEEPALIVE, Boolean.TRUE);
    }
}
public static void main(String[] args) {
    try {
        Socket sock = SocketBuilder.createCVPSocket();
        System.out.println(sock);
    } catch (Exception e) { 
        e.printStackTrace();
    }
}

}

Answer 2

如果查看AbstractPlainSocketImpl#setOption方法的源代码，

public void setOption(int opt, Object val) throws SocketException {
        if (isClosedOrPending()) {
            throw new SocketException("Socket Closed");
        }
// Rest of the code removed for brevity
}

在设置选项之前，您可以看到isClosedOrPending检查。

 /*
 * Return true if already closed or close is pending
 */
public boolean isClosedOrPending() {
    /*
     * Lock on fdLock to ensure that we wait if a
     * close is in progress.
     */
    synchronized (fdLock) {
        if (closePending || (fd == null)) {
            return true;
        } else {
            return false;
        }
    }
}

在您的情况下，由于您只是创建一个套接字，它将不会有任何与之关联的fd。这就是你得到这个错误的原因。

SocketImpl Setoption中的套接字闭合异常

2 个答案: