Java PatternSyntaxException: Unmatched closing '('

Question

I need to remove all the URLs found in Twitter messages. I have a file with around 200,000 such messages so speed is crucial! To do this I use Java as a programming language, here is an example of my code: ``` public String performStrip(){ String tweet = this.getRawTweet(); String urlPattern = "((https?|http)://(bit\.ly|t\.co|lnkd\.in|tcrn\.ch)\S*)\b"; Pattern p = Pattern.compile(urlPattern,Pattern.CASE_INSENSITIVE); Matcher m = p.matcher(tweet); int i = 0; while (m.find()) { tweet = tweet.replaceAll(m.group(i),"").trim(); i++; } return tweet; } ``` This works fine in following cases: ``` http://t.co/nhWp9hldEH -> (empty string) http://t.co/nhWp9hldEH" -> " http://t.co/nhWp9hldEH)aaa" -> aaa" aaa(http://t.co/nhWp9hldEH" -> aaa(" aaa(http://t.co/nhWp9hldEH)" -> aaa()" ``` However, when I get to a case as follows: ``` http://t.co/nhWp9hldEH)aaa" ``` I get an error ``` java.util.regex.PatternSyntaxException: Unmatched closing ')' near index 21 ``` http://t.co/nhWp9hldEH)aa ``` at j…

Accepted Answer

The problem is that you may have regex special characters in a URL, as you can see.

Short solution: use `Pattern.quote()`. Your code would then be:

```
tweet = tweet.replaceAll(Pattern.quote(m.group(i)),"").trim();
```

Note: only available since JDK 1.5, but you do use this or better, right?

Another solution is to simply use `.replace()`:

```
tweet = tweet.replace(m.group(i), "").trim();
```

Unlike what its name suggests with regards to `.replaceAll()`, `.replace()` does replace all occurrences; it is simply that it doesn't take a regex as a replacement string. See also `.replaceFirst()`.

Last but not least, you seem to be misusing `.group()`! Your loop should be:

```
while (m.find())
    tweet = tweet.replace(m.group(), "").trim();
```

No need for the `i` variable here; `m.group(i)` will, for one match, return what is matched by capturing group `i` in your regex.

Java PatternSyntaxException: Unmatched closing '('

Solution

Problem