Pattern matching with Java regex

Question

My server dev gave me a regex that he says is the requirement for user name. It is @"^\w+([\s-]\w+)*$"

I need help figuring out right Java expression for this. It is confusing since I need to put some escape characters to make compiler happy.

I am trying this. Please let me know if this is right :

Pattern p = Pattern.compile("^\\w+([\\s-]\\w+)*\\$", Pattern.CASE_INSENSITIVE);

   Matcher m = p.matcher(username);

   if ((username.length() < 3 ) || (m.find())) {
      log ("Invalid pattern"); 
      return false;
   }

Is this correct ?

Wagner DosAnjos · Accepted Answer · 2016-11-03 03:21:51Z

3

The correct pattern is "^\\w+([\\s-]\\w+)*$".

$ denotes the end of the string, if you use \\$ it will force the string to have the char $ and that's not the intent.

answered Nov 3, 2016 at 3:21

Wagner DosAnjos

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5 Comments

techtinkerer Over a year ago

Thanks. So, what is this regex actually saying ? I understand \w is a word. So, does it mean, a name will be [word] optional : - or space or * followed by another word ?

techtinkerer Over a year ago

should john* be a valid name then ?

Wagner DosAnjos Over a year ago

^ is the beginning of the string, that should have at least one (+) word char (\w -> a-z or 0-9) followed by zero or more (*) occurrences of a space char (\s) or a dash (-) followed by at least one (+) word char (\w).

techtinkerer Over a year ago

thanks. So, john* (john followed by asterix) is invalid then ?

Wagner DosAnjos Over a year ago

john* is invalid in your case.

Raman Sahasi · Accepted Answer · 2016-11-03 03:22:42Z

2

In your regex

^\\w+([\\s-]\\w+)*\\$
                    ^

You don't have to escape this $. It is there to indicate End Of Line.

so the correct Regex would be:

^\\w+([\\s-]\\w+)*$

N.B.: However, you have to make sure that this $ sign doesn't represent $ literally. In that case you'd have to escape it, but I anticipate in that case it would be escaped in your source RegEx as well.

answered Nov 3, 2016 at 3:22

Raman Sahasi

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2 Comments

techtinkerer Over a year ago

thanks for the additional clarification. The name didnt require an explicit dollar sign. I guess this is just a end marker of the name.

Raman Sahasi Over a year ago

@techtinkerer ya. I think in that case you should use RegEx ^\\w+([\\s-]\\w+)*$

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