java aio SO_KEEPALIVE not supported in ubuntu 16.04?

Question

I am testing java AsynchronousServerSocketChannel, but when I tried set SO_KEEPALIVE=true, a error message showed me that not support it? How to fix below issues? It is really not support keep-alive in ubunut server?

The code is:

private void init(String host, int port) {
    try {
        final AsynchronousChannelGroup group = AsynchronousChannelGroup.withCachedThreadPool(Executors.newCachedThreadPool(), 10);
        final AsynchronousServerSocketChannel server = AsynchronousServerSocketChannel
                .open(group).bind(new InetSocketAddress(host, port))
                .setOption(StandardSocketOptions.SO_KEEPALIVE, true)
                .setOption(StandardSocketOptions.TCP_NODELAY, true)
                .setOption(StandardSocketOptions.SO_REUSEADDR, true)
                .setOption(StandardSocketOptions.SO_RCVBUF, 16 * 1024);
        System.out.println("Listening on: " + host + ":" + port);
        System.out.println("Channel Provider : " + server.provider());
        server.accept(null, new handler());
        group.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS);
        //TimeUnit.DAYS.sleep(Long.MAX_VALUE);
    } catch (IOException | InterruptedException ex) {
        Logger.getLogger(AIOEchoServer.class.getName()).log(Level.SEVERE, null, ex);
    }
}

private class handler implements CompletionHandler<AsynchronousSocketChannel, Void> {

    @Override
    public void completed(AsynchronousSocketChannel result, Void attachment) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }

    @Override
    public void failed(Throwable ex, Void attachment) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }
}

The error is:

Exception in thread "main" java.lang.UnsupportedOperationException: 'SO_KEEPALIVE' not supported
at sun.nio.ch.AsynchronousServerSocketChannelImpl.setOption(AsynchronousServerSocketChannelImpl.java:187)
at TestAIO.AIOEchoServer.init(AIOEchoServer.java:28)
at TestAIO.AIOEchoServer.main(AIOEchoServer.java:20)

Answer 1

You're using a AsynchronousServerSocketChannel, i.e. a listening socket which can only accept new incoming connections and not exchange data. The socket option simply is not applicable to a listening socket.

The class documentation states as much.

You should set those options on the new socket you get from accept()