Java Regex Escape

Question

I've got this bit of code to grab a url within a textarea. It has been working great until I tried a url with a '+' in it.

Pattern pattern = Pattern.compile("(.*)(https?[://.0-9-?a-z=_#!A-Z]*)(.*)");
Matcher matcher = pattern.matcher(text);

So I tried puting \\+ and \\\\+ in my code but it did not work. So i did some googling and stack overflow problems kept mentioning this guy

Pattern.quote("+");

However, I am not sure how I implement that statement into what I currently have now. If that is even the way I want to go. But I'm assuming I need to do something like this...

String quote = Pattern.quote("+");
Pattern pattern = Pattern.compile("(.*)(https?[://.0-9-?a-z=_#!A-Z]*)(.*)");
Matcher matcher = pattern.matcher(text);

And then add the variable quote somewhere in the pattern? Please help! I just learned this stuff today I'm brand new to it! Thank you?

John Woo · Accepted Answer · 2012-10-17 05:22:17Z

3

just escape the quote with \, example

Pattern pattern = Pattern.compile("(.*)(https?[://.0-9-?a-z=_#!A-Z\"]*)(.*)");

answered Oct 17, 2012 at 5:22

John Woo

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5 Comments

Bohemian Over a year ago

remove the // too. a) it should be \\, and b) you don't need to escape dots within a character class

gmustudent Over a year ago

like this? Pattern pattern = Pattern.compile("(.*)(https?[://.0-9-?a-z=_#!A-Z\"quote\"]*)(.*)");

John Woo Over a year ago

@Bohemian, i don't get it. why would you remove //? i think it didn't escape dots.

gmustudent Over a year ago

Unfortunately it is not escaping the +'s for me with the new code. Are you sure I just put the string into the pattern?

John Woo Over a year ago

@gmustudent how about this? (.*)(https?[://.0-9-?\\+a-z=_#!A-Z\"]*)(.*)

Jeff Bowman · Accepted Answer · 2012-10-17 05:34:05Z

1

(https?[://.0-9-?a-z=_#!A-Z]*)

Bear in mind that [ and ] denote a class of characters, and that this means that any character within it will be included. [aegl]+ will match "age", "a", "e", g", "eagle", and "gaggle". It also means that a character listed twice (like /) is completely redundant.

Pattern.quote is useful, but will only return the same string with a backslash preceding any special character. Pattern.quote("+") will return \+.

Because + has no significance between square brackets, you should be able to put a + unescaped within the square brackets. At that point you can also add a \\ if it makes you feel better.

Pattern pattern = Pattern.compile("(.*)(https?[:/.0-9-?a-z=_#!A-Z+]*)(.*)");
Pattern pattern = Pattern.compile("(.*)(https?[:/.0-9-?a-z=_#!A-Z\\+]*)(.*)");

See it here: http://fiddle.re/0780

answered Oct 17, 2012 at 5:34

Jeff Bowman

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2 Comments

gmustudent Over a year ago

Thank you so much for the explanation. It cleared up a lot of things for me and I learned quite a bit. unfortunately this seems to be working great in the console but breaks down in my web app every time. It just hates the + sign for some reason and won't read it I don't understand why.

Jeff Bowman Over a year ago

@gmustudent Sounds tricky. Maybe I can help you in a SO chat room.

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