An nslookup clone in Java
import java.io.DataInputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
/**
* An "nslookup" clone in Java.
*
* @author Elliot Rusty Harold, O'Reilly & Associates
*/
public class JavaLookup {
public static void main(String args[]) {
if (args.length > 0) { // use command line
for (int i = 0; i < args.length; i++) {
lookup(args[i]);
}
} else {
DataInputStream myInputStream = new DataInputStream(System.in);
System.out
.println("Enter names and IP addresses. Enter \"exit\" to quit.");
while (true) {
String s;
try {
s = myInputStream.readLine();
} catch (IOException e) {
break;
}
if (s.equals("exit"))
break;
if (s.equals("quit"))
break;
if (s.charAt(0) == '\004')
break; // unix ^D
lookup(s);
}
}
} /* end main */
private static void lookup(String s) {
InetAddress thisComputer;
byte[] address;
// get the bytes of the IP address
try {
thisComputer = InetAddress.getByName(s);
address = thisComputer.getAddress();
} catch (UnknownHostException ue) {
System.out.println("Cannot find host " + s);
return;
}
if (isHostname(s)) {
// Print the IP address
for (int i = 0; i < address.length; i++) {
int unsignedByte = address[i] < 0 ? address[i] + 256
: address[i];
System.out.print(unsignedByte + ".");
}
System.out.println();
} else { // this is an IP address
try {
System.out.println(InetAddress.getByName(s));
} catch (UnknownHostException e) {
System.out.println("Could not lookup the address " + s);
}
}
} // end lookup
private static boolean isHostname(String s) {
char[] ca = s.toCharArray();
// if we see a character that is neither a digit nor a period
// then s is probably a hostname
for (int i = 0; i < ca.length; i++) {
if (!Character.isDigit(ca[i])) {
if (ca[i] != '.') {
return true;
}
}
}
// Everything was either a digit or a period
// so s looks like an IP address in dotted quad format
return false;
} // end isHostName
} // end javalookup
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