不靠谱的InetAddress.isReachable，解决办法

public static final boolean isNodeReachable(String hostname) {
        try {
            InetAddress address = InetAddress.getByName(hostname);
            if (address.isReachable(3000)) {
                return true;
            } else {
                return false;
            }
        } catch (Exception e) {
            System.out.println(hostname + "网络不可达！");
            e.printStackTrace();
            return false;
        }
    }

public static final boolean isNodeReachable(String hostname) {
        try {
            return 0==Runtime.getRuntime().exec("ping -c 1 "+hostname).waitFor();
        } catch (InterruptedException | IOException e) {
            e.printStackTrace();
            return false;
        }
    }