Validating website address
Input validation, as you likely know, ensures that a program operates on clean and usable data.
There are several tools in common use for locating webpages that are vulnerable to missing input validation.
As may be seen in the reference, to check a numeric representation, there may be 1 to 4 parts, and in each case different limitations on the parts apply.
I would suggest using what's available on the platform/framework you are developing.
class and instanciate it by giving it a string representation of the the ip address.
This way you can split out the different validation steps into instance methods and get some separation of concern going.
If you expect a lot of hostnames as parameters, beware that this implementation uses DNS to try to resolve it. Otherwise you can have a peak into In think this solution is quite elegant, although it takes a minute to understand it.
This is not always desired (for more complicated data, it will probably be much easier to take a look, correct that one typo and continue with the rest of the form), so my preference is actually to mark the field so that the user knows which field needs to be corrected, and have the validation script not report a validation error back to the field: Using this method has implications on the form submission process: The form no longer can verify that the data is correct, so the submission function needs to do another round of validation to see if any of the required fields are not correct (one way to do that is to test all relevant fields to see if the text color is using the error color, or we can use global variables to store the validation state).For instance, this here is typically it's own method, call this simply Now that you have this, if you ever want to extend this class to also look for if the IP is localhost or if it is a broadcast address, it is pretty easy to do this. You can also tell exactly which one of your validation rules was broken in the validation of the IP address string. Most of the answers (except that of Michael Konietzka) are wrong: 10.8, for instance, is a valid IP4 address (a shorthand for 10.0.0.8).See Textual representation of IP addresses in the Java specifications.Please note that I switch x and y, since the start of a sub-string will always be the end of the last one plus 1.This solution is about 20x faster than a regex variant and 2x faster than splitting.