Problems with matching emails with regex

I'm trying to match an email address here is what I've come up with so far :

String text = "gandalf_storm@mymail.com"; 
String regex = "(\\w+)@{1}(\\w+){2,}\\.{1}\\w{2,4}";

This however works with following cases :

gandalf_storm@mymail.com

gandalfstorm@mymail.com

gandalf2storm@mymail.com

So it matches any alphanumeric character repeated once or more that comes before one @ followed by any alphanumeric character repeated at least two times(which is minimal characters for any domain name) followed by one .(dot) and followed by any alphanumeric character repeated at least 2 times and at most 4 times(because there are domains such as .us or .mobi).

This expression however does not work with emails such as :

gandalf.storm@mymail.com gandalf.storm@mydomain.me.uk gandalf.storm@mysubdomain.mydomain.me.uk gandalf.storm@mysubdomain.mysubdomain.mydomain.me.uk etc as many subdomains

or

gandalf.storm@mymail.c开发者_运维问答om gandalf2storm@mydomain.me.uk gandalf_storm@mysubdomain.mydomain.me.uk gandalfstorm@mysubdomain.mysubdomain.mydomain.me.uk

I've just started to learn regex and I found interesting to try to solve problems such as these by using regex .. not partially but for each case, any help would be much appriciated. Thank you

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This question has been asked many, many times before here on SO. Here's why you don't want to use regexes to parse email addresses. Note please that that monster of a regex doesn't even handle comments.

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see this question. Particularly the answer from Good Person. This article has some code for validating an email address.

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The regex you use is very restrictive :

• Using the \w character class before the @ does not allow the . character, which explains why gandalf.storm does not match
• In the domain part of the regex, you only allow two "words" separated with a . character, which excludes "mysubdomain.mydomain.net"

You should try to fix these to match your more complicated examples.

As a side note, when you want to match a single character, the {1} part is not mandatory.

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To answer your question, as you are learning.

The problem with your regex not matching with the first lot is partly because the part before the @ does not allow the '.' character. changing to this:

 String regex = "([\\w.]+)@(\\w+){2,}\\.\\w{2,4}";

should allow gandalf.storm@mymail.com, because the [\\w.]+ says any character in the group '\w' (any character) or '.' (does not need to be escaped when part of a group, actually means a dot) 1 or more times

This might give you enough of a help to be able to figure the rest out on your own. after all that is the point of learning :)

I tested this at http://www.regexplanet.com/simple/index.html which uses the java library for the engine.