Java regex to extract host name and domain name from a URL

Question

I have already viewed and tried multiple other threads and doesn't work for me. I need the regex solution for it to work and no java code that does it without regex.

Some of the threads which I have already checked: Get domain name from given url, Extract host name/domain name from URL string, and Java regex to extract domain name? None work for me, either the regex doesn't work or the solution is a java code without regex.

What I am trying to do?

Case 1:
Input: https://api.twitter.com/blog/category/2?user=42&status=enabled
Output: api.twitter.com

Input: abc.xyz.com/blog/category/2?user=42&status=enabled
Output: abc.xyz.com

Case 2:
Input: https://abc.xyz.com/blog/category/2?user=42&status=enabled
Output: xyz.com

Input: abc.xyz.com/blog/category/2?user=42&status=enabled
Output: xyz.com

I need 2 regexes to solve each case mentioned above. If it can be done in one, even that works.

I tried the below regex from the first post:

^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?

This one works when there is https:// or any scheme but fails when there is no scheme in the URL.

So far I am solving the first case using a 2 step solution.

Step 1: Replace scheme
(.*://)(.*) -> $2
remove anything before and including string "://"

Step 2: Extract host name
([^/]*)(.*) -> $1
The first group extracts everything that is before the first "/". Basically extracting everything that isn't slash till I see the first one.

Why is the abc not part of the output in case 2 and how would a regex know when to use which? — geanakuch
– geanakuch, Commented Jun 8, 2021 at 5:36
Do you understand the regexp you quoted? (As in, enough to debug and maintain it) — Thorbjørn Ravn Andersen
– Thorbjørn Ravn Andersen, Commented Jun 8, 2021 at 5:38
For case 2, I can use 2 step solution. If case 1 works for me. First, extract the hostname then the domain name from it. — Bikas Katwal
– Bikas Katwal, Commented Jun 8, 2021 at 5:39
@BikasKatwal: Why does output #2 show abc.xyz.com but output #3 and #4 show only xyz.com? — anubhava
– anubhava, Commented Jun 8, 2021 at 6:30
@anubhava thanks! that works :) Could you add this as the answer? and I will use this .* instead of https. As the scheme can be anything, forgot to mention it in question. — Bikas Katwal
– Bikas Katwal, Commented Jun 8, 2021 at 7:02

anubhava · Accepted Answer · 2021-06-08 07:04:10Z

4

You may use this regex with optional matches and capture groups:

^(?:\w+://)?((?:[^./?#]+\.)?([^/?#]+))

RegEx Demo

RegEx Details:

^: Start
(?:\w+://)?: Optionally match scheme names followed by ://
(: Start capture group #1
- (?:[^./?#]+\.)?: Optionally match first part of domain name using a non-capture group
- ([^/?#]+): Match 1+ of any character that is not /, ?, # in capture group #2
): End capture group #1

answered Jun 8, 2021 at 7:04

anubhava

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