hostLookUp

/*
* Main.java
*
* Created on 2006年11月11日, 下午12:30
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/

package javaapplication2;

/**
*
* @author Star
*/
import java.net.*;
import java.io.*;

public class HostLookup {

public static void main (String[] args) {

if (args.length > 0) { // use command line
for (int i = 0; i <>
System.out.println(lookup(args[i]));
}
}
else {
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter names and IP addresses. Enter \"exit\" to quit.");
try {
while (true) {
String host = in.readLine();
if (host.equalsIgnoreCase("exit") || host.equalsIgnoreCase("quit")) {
break;
}
System.out.println(lookup(host));
}
}
catch (IOException ex) {
System.err.println(ex);
}

}

} /* end main */


private static String lookup(String host) {

InetAddress node;

// get the bytes of the IP address
try {
node = InetAddress.getByName(host);
}
catch (UnknownHostException ex) {
return "Cannot find host " + host;
}

if (isHostname(host)) {
return node.getHostAddress();
}
else { // this is an IP address
return node.getHostName();
}

} // end lookup

private static boolean isHostname(String host) {

// Is this an IPv6 address?
if (host.indexOf(':') != -1) return false;

char[] ca = host.toCharArray();
// if we see a character that is neither a digit nor a period
// then host is probably a hostname
for (int i = 0; i <>
if (!Character.isDigit(ca[i])) {
if (ca[i] != '.') return true;
}
}

// Everything was either a digit or a period
// so host looks like an IPv4 address in dotted quad format
return false;

} // end isHostName

} // end HostLookup