java - Regular expression to retrieve domain.tld

Question

I'm need a regular expression in Java that I can use to retrieve the domain.tld part from any url. So https://foo.com/bar, http://www.foo.com#bar, http://bar.foo.com will all return foo.com.

I wrote this regex, but it's matching the whole url

Pattern.compile("[.]?.*[.x][a-z]{2,3}");

I'm not sure I'm matching the "." character right. I tried "." but I get an error from netbeans.

Update:

The tld is not limited to 2 or 3 characters, and http://www.foo.co.uk/bar should return foo.co.uk.

Answer 1

This is harder than you might imagine. Your example https://foo.com/bar, has a comma in it, which is a valid URL character. Here is a great post about some of the troubles:

https://blog.codinghorror.com/the-problem-with-urls/

https?://([-A-Za-z0-9+&@#/%?=~_()|!:,.;]*[-A-Za-z0-9+&@#/%=~_()|])

Is a good starting point

Some listings from "Mastering Regular Expressions" on this topic:

http://regex.info/listing.cgi?ed=3&p=207

@sjobe

>>> import re
>>> pattern = r'https?://([-A-Za-z0-9+&@#/%?=~_()|!:,.;]*[-A-Za-z0-9+&@#/%=~_()|])'
>>> url = re.compile(pattern)
>>> url.match('http://news.google.com/').groups()
('news.google.com/',)
>>> url.match('not a url').groups()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'groups'
>>> url.match('http://google.com/').groups()
('google.com/',)
>>> url.match('http://google.com').groups()
('google.com',)

sorry the example is in python not java, it's more brief. Java requires some extraneous escaping of the regex.