How can use java emulate ping function?

Question

When I type ping xxx.x.xx.x,it would send a icmp package.
If the remote mechine has no echo,it would wait too long.
So Making a runtime process to invoke ping command directly is not efficient.
My single aim is showing the remote mechine exiting or not on web page.
Any idea appreciate

Answer 1

Runtime.exec,I know,but it's too long to wait if the mechine has no echo.
The checked machine is not the pc,but the "set top box".
Assume there are no firewall to block any port and any protocol.
It can telnet to the STB by No.25 port.
But when I use socket connection,it has no response.
It's very weird.
I have successfully to check the PC by this way.
Anyway,this way also wait too long,although I have set the time out value.It has no use.
BTW,I have search the forums again, some one write native C to emualte icmp.I still not test it and hope it not use that complex way.
package TEST;
import java.net.*;
import java.io.*;
* Useful to know if you can connect to a computer
* Port 13 is the date time port
* Port 7 is the echo port
* Port 23 is the Telnet service port
* Port 25 is the E-Mail port
public class PING {
    public static void main (String [] args) {
        if(args.length !=2){
            System.out.println("Usage: java ping ");
            System.exit(0);
        String computer = args[0];
        int dayTimePort = 13; //each computer uses this port for date and time
        dayTimePort = Integer.parseInt(args[1]);
        BufferedReader in = null;
        Socket socketComputer = null;
        try{
            System.out.println(computer + ":" + dayTimePort);
            socketComputer = new Socket(computer,dayTimePort);
            socketComputer.setSoTimeout(1000);
            in = new BufferedReader( new InputStreamReader( socketComputer.getInputStream() ) );
            String timeStamp = in.readLine();
            System.out.println( computer + " is alive at " + timeStamp );
        }catch (UnknownHostException e) {
            System.err.println( "Don't know about host: " + computer );
            System.exit( 1 );
        }catch (IOException e) {
            System.err.println( "Couldn't get I/O for " + "the connection to: " + computer + e.getMessage());
            System.exit( 1 );
    } // end main
} // end class ping.java