Java Regex: Matcher.find problems

Question

I am having trouble distinguishing two templates when I aplly match.find().

String template1 = "GET /boards/(.+?)";
String template2 = "GET /boards/(.+?)/lists";

When given the following input : "GET /boards/boardName/lists" , it matches with the first template instead of the second. What am I doing wrong ?

Thanks in advance

In the first one, +? will still match (non-greedily) the character after the last forward slash because . matches any single character except newline. Therefore, it matches on this expression first. If you don't want the first expression to match, change it to GET /boards/([^/]+)$ — hwnd
– hwnd, Commented Oct 17, 2015 at 20:12
In the first case, group 1 contains boardName/lists. In the second case group 1 contains boardName. Both patterns will match. — Boris the Spider
– Boris the Spider, Commented Oct 17, 2015 at 20:13

Kasravnd · Accepted Answer · 2015-10-17 20:47:16Z

1

That's because of that (.+?) will match every combinations of characters with length 1 or more which will make your regex engine match the following part :

boardName/lists

Also note that if you first try the following regex :

GET /boards/(.+?)/lists

It will match the string too but the difference is that in this regex the group 1 will be contain boardName, but in the first one the group 1 will be b (because of ? which makes .+ a none greedy pattern ).

If you want that the first regex not match your string you can use a negative look ahead and a negated character class to match the strings that are not followed by word list :

GET /boards/([^/]+)(?!lists)

edited Oct 17, 2015 at 20:47

answered Oct 17, 2015 at 20:12

Kasravnd

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3 Comments

Kasravnd Over a year ago

@hwnd Yep, that will match the strings that just have one word after GET /boards/.

YoungHobbit Over a year ago

Can you please check this: ideone.com/u75KTR I am getting different output then what you have mentioned.

Kasravnd Over a year ago

@YoungHobbit yep, sorry I missed that point, the first regex group 1 will be the character b because of none greedy matching

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