How to parse IP Address or Host name containing Alpha Characters?

Question

I am trying to separate two different types of Strings, IP addresses and DNS addresses. I am having trouble figuring out how to split it. My initial thought is:

String stringIP = "123.345.12.1234";
String stringDNS = "iam.adns234.address.com";

if(!Pattern.matches("^[a-zA-Z0-9.]*$",stringDNS)){
    //I only want to get IP type strings here, so I am trying to separate out anything containing alpha characters. `stringDNS` should not be allowed into the if statement.
}

Answer 1

You can "validate" your IP with the following pattern:

String stringIP = "123.345.12.1234";
String stringDNS = "iam.adns234.address.com";
//                | start of input
//                | | 1-4 digits
//                | |      | dot
//                | |      |    | 3 occurrences
//                | |      |    | | 1-4 digits
//                | |      |    | |       | end of input
String pattern = "^(\\d{1,4}\\.){3}\\d{1,4}$";
System.out.println(stringIP.matches(pattern));
System.out.println(stringDNS.matches(pattern));

Output

true
false

Note

Validation here is "lenient", insofar as it won't check the values and will fit your example with up to 4 digit items.

For a more serious validation (with the down side of a less readable pattern), see dasblinkenlight's answer.