best Alternative for InetAddress.getByName(host).isReachable(timeout)

Question

I am trying to reach a host and have the following code

if(!InetAddress.getByName(host).isReachable(TIMEOUT)){
   throw new Exception("Host does not exist::"+ hostname);
 }

The hostname I am able to ping from windows, and also did a tracert on it and it returns all the packets. But java throws out exception "Host does not exist::";

The Timeout value I experimented from giving 2000ms, to 5000ms. I tried 3000 as well. What is the cause of this problem I am not able to understand. I researched on the net and some say that InetAddress.getByName(host).isReachable(time) is not reliable and behaves according to the internal system.

What is the best alternative for this if this is true. Please suggest.

Answer 1

Either open a TCP Socket to a port you think is open (22 for Linux, 139 for Windows, etc.)

public static boolean isReachableByTcp(String host, int port, int timeout) {
    try {
        Socket socket = new Socket();
        SocketAddress socketAddress = new InetSocketAddress(host, port);
        socket.connect(socketAddress, timeout);
        socket.close();
        return true;
    } catch (IOException e) {
        return false;
    }
}

Or use some hack to send an actual ping. (inspired from here: http://www.inprose.com/en/content/icmp-ping-in-java)

public static boolean isReachableByPing(String host) {
    try{
        String cmd = "";

        if(System.getProperty("os.name").startsWith("Windows"))
            cmd = "cmd /C ping -n 1 " + host + " | find \"TTL\"";
        else
            cmd = "ping -c 1 " + host;

        Process myProcess = Runtime.getRuntime().exec(cmd);
        myProcess.waitFor();

        return myProcess.exitValue() == 0;
    } catch( Exception e ) {
        e.printStackTrace();
        return false;
    }
}

Same hack for Android can be found here: