Analysis of the IPV4 address function of regular expression validation

Source: Internet
Author: User
This example describes the regular expression validation IPV4 address feature. Share to everyone for your reference, as follows:

The IPV4 address consists of 4 groups of numbers, separated by a., and the range of values for each group of numbers is 0-255.

IPV4 must meet the following four rules:

1. Any 1-digit or 2-digit number, or 0-99;
2. Any 3-digit number starting with 1, or 100-199;
3, any one starting with 2, the 2nd digit is 0-4 between 3 digits, that is, 200-249;
4, any one beginning with 25, the 3rd digit in the 0-5 between the 3 digits, namely 250-255.

The idea of constructing a regular expression is clear after all the rules are listed.

The first rule that satisfies the first one is: \d{1,2}
The first rule that satisfies the second one is: 1\d{2}
The first rule that satisfies the third one is: 2[0-4]\d
The first rule that satisfies fourth rules is: 25[0-5]

By grouping them together, you get a regular expression that matches 0-255 numbers:

(\d{1,2}) | (1\d{2}) | (2[0-4]\d) | (25[0-5])

The IPV4 consists of four groups of numbers, separated by., or by three numbers and characters. And a set of numbers, so the regular expression that matches the IPV4 is as follows:

((\d{1,2}) | (1\d{2}) | (2[0-4]\d) | (25[0-5])) \.) {3} ((\d{1,2}) | (1\d{2}) | (2[0-4]\d) | (25[0-5]))

The Java test code is as follows:

public static void Matchandprint (string regex, String sourcetext) {  Pattern pattern = pattern.compile (regex);  Matcher Matcher = Pattern.matcher (sourcetext);  while (Matcher.find ()) {    System.out.println (Matcher.group ());}  } public static void Main (string[] args) {  String regex = "^ ((\\d{1,2}) | ( 1\\D{2}) | (2[0-4]\\d) | (25[0-5])) \\.) {3} ((\\d{1,2}) | (1\\d{2}) | (2[0-4]\\d) | (25[0-5])) $";  Matchandprint (Regex, "23.135.2.255");  Matchandprint (Regex, "255.255.0.256");  Matchandprint (Regex, "0.0.0.0");}

The output results are as follows:

23.135.2.255
0.0.0.0

This regular has a flaw, that is, if you do not use boundary matching, like the second Test IP 255.255.0.256 will also be matched to the result of matching is 255.255.0.25. You can add a constraint, either before or after a boundary, or a non-numeric, and use the front and back lookup (Lookaround), which is described later. That

(? <= (\\b|\\d)) ((\d{1,2}) | (1\d{2}) | (2[0-4]\d) | (25[0-5])) \.) {3} ((\d{1,2}) | (1\d{2}) | (2[0-4]\d) | (25[0-5])) (? = (\\b|\\d))

String regex = "(? <= (\\b|\\d)) ((\\d{1,2}) | ( 1\\D{2}) | (2[0-4]\\d) | (25[0-5])) \\.) {3} ((\\d{1,2}) | (1\\d{2}) | (2[0-4]\\d) | (25[0-5])) (? = (\\b|\\d)) ";

This solves the problem.

It is hoped that this article will be helpful to everyone's regular expression learning.

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.