Java Regex

Hi,
I am new to Java Regex, i have a requirement in which i need to write java regex for validating ip address keeping in mind the below points.
Basically i need to validate the search key word, which a user enters.

1) IP-address notation dictates that is consists of 4 “dotted-decimals” – i.e. 4 “digit strings” that are separated by a “.” (dot).
Each dotted-decimal is between 1-3 digits long and value of a dotted-decimal number must be between 0-255 to be valid.
Example of valid IP-address notation: 0.0.0.0 or 1.2.3.4 or 23.34.45.56 or 255.255.255.255 (>256 is not valid)

2) Example of allowed inputs:

a) dotted-decimal: .1 or 1. (note: could be with or without leading/trailing “.” !)
b) dotted-decimals: 1.2 or .2.3 or .2.3. or .3.4 (note: could be with or without leading/trailing “.” !)
c) dotted-decimals: 1.2.3 or 1.2.3. or .2.3.4 (note: could be with or without leading/trailing “.” !)
d) dotted-decimals: 1.2.3.4 (note: could be with or without leading/trailing “.” !)

Need Regex pattern for the above.

Thanks in Advance.

Regards,

Girish

These two articles will be of help- Lesson: Regular Expressions and Regular Expressions and the Java Programming Language

The second article is concise.

Thanks Mohamed,
since the conditions are very confusing, can you give me some hint on how to proceed.

Welcome to the Ranch

The conditions for a valid IP address are actually very simple, and you have already described them.
Not sure how you manage not greater than 255, however.

I would not use regex to evaluate an ip address. Well I am but only because there is no other standard way:

Split the ip on the "." You'll have to use "\\." because the argument is a regex pattern and the dot needs to be escaped.
Parse every segment to an int and check its value.

(Are you keeping IPv6 in mind?)

Campbell Ritchie wrote:Not sure how you manage not greater than 255, however.

group() method of Matcher to extract each octet, then Integer.parseInt to check that the octet is in the right range.