extract a substring in Java

Question

I have the following string:

"hello this.is.a.test(MainActivity.java:47)"

and I want to be able to extract the MainActivity.java:47 (everything that is inside '(' and ')' and only the first occurance).

I tried with regex but it seems that I am doing something wrong.

Thanks

posiible duplicates of http://stackoverflow.com/questions/4749549/extract-substring-in-java-using-regex and http://stackoverflow.com/questions/4662215/java-how-to-extract-a-substring-using-regex — Saurabh Gokhale, Mar 17 '11 at 14:28
Do you specifically _need_ to use a regex, or is any working method sufficient? — Pops, Mar 17 '11 at 14:30
it looks like you're trying to parse a stacktrace. It comes from a text file, or do you have access to the Exception object being created? — Soronthar, Mar 17 '11 at 14:42

Aaron Digulla · Answer 1 · 2011-03-17T16:43:11.803

4

You can do it yourself:

int pos1 = str.indexOf('(') + 1;
int pos2 = str.indexOf(')', pos1);

String result = str.substring(pos1, pos2)

Or you can use commons-lang which contains a very nice StringUtils class that has substringBetween()

edited Mar 17 '11 at 16:43

answered Mar 17 '11 at 14:27

Aaron Digulla

321,842
108
597
820

1

I think you need to replace the line: `int pos1 = str.lastIndexOf('(') + 1;` with `int pos1 = str.indexOf('(') + 1;`. The OP wants only the first occurence. – Mihai Toader Mar 17 '11 at 14:46
@Toader: Maybe. I've upvoted your comment to make it more prominent. That way, the OP can decided what he needs. – Aaron Digulla Mar 17 '11 at 14:49
1

thanks .. This is what he said: "and only the first occurance." – Mihai Toader Mar 17 '11 at 14:50

score 1 · Answer 2 · answered Mar 17 '11 at 14:28

I think Regex is a liitle bit an overkill. I would use something like this:

String input = "hello this.is.a.test(MainActivity.java:47)";
String output = input.subString(input.lastIndexOf("(") + 1, input.lastIndexOf(")"));

score 1 · Answer 3 · answered Mar 17 '11 at 14:28

1

This should work:

^[^\\(]*\\(([^\\)]+)\\)

The result is in the first group.

answered Mar 17 '11 at 14:28

Mihai Toader

12,041
1
29
33

1

Sure you *could* do it with a regex, but when it looks like that, why bother? – Daniel DiPaolo Mar 17 '11 at 14:30
1

ACtually the actual regex is much simpler :). I just complicated it to make sure it works as intended :). This will work too: `\$(.+?)\$` – Mihai Toader Mar 17 '11 at 14:33
Two reasons to bother about regexes: the "lastIndexOf" method will iterate over the chars of the string twice (once for the "(", once for the ")") while a good regex implementation will iterate over the chars just once (twice, in the worst case, depending on the output). The second is that you may have unbalanced (). In the special case of the OP, they are balance so my second point is moot. – Soronthar Mar 17 '11 at 14:37
... and the doubled backslashes are not part of the regexp, only necessary for the Java String literal. – Paŭlo Ebermann Mar 17 '11 at 14:45

score 1 · Answer 4 · answered Mar 17 '11 at 17:32

Another answer for your question :


String str = "hello this.is.a.test(MainActivity.java:47) another.test(MyClass.java:12)";
Pattern p = Pattern.compile("[a-z][\\w]+\\.java:\\d+", Pattern.CASE_INSENSITIVE);
Matcher m=p.matcher(str);

if(m.find()) {
    System.out.println(m.group());
}

The RegExp explained :

[a-z][\w]+\.java:\d+

[a-z] > Check that we start with a letter ...
[\w]+ > ... followed by a letter, a digit or an underscore...
\.java: > ... followed exactly by the string ".java:"...
\d+ > ... ending by one or more digit(s)

score 0 · Answer 5 · answered Mar 17 '11 at 14:29

0

Pseudo-code:

int p1 = location of '('
int p2 = location of ')', starting the search from p1
String s = extract string from p1 to p2

String.indexOf() and String.substring() are your friends.

answered Mar 17 '11 at 14:29

Bombe

81,643
20
123
127

score 0 · Answer 6 · answered Mar 17 '11 at 14:42

Try this:

String input = "hello this.is.a.test(MainActivity.java:47) (and some more text)";
Pattern p = Pattern.compile("[^\\)]*\\(([^\\)]*)\\).*");
Matcher m = p.matcher( input );
if(m.matches()) {
  System.out.println(m.group( 1 )); //output: MainActivity.java:47
}

This also finds the first occurence of text between ( and ) if there are more of them.

Note that in Java you normally have the expressions wrapped with ^ and $ implicitly (or at least the same effect), i.e. the regex must match the entire input string. Thus [^\\)]* at the beginning and .* at the end are necessary.

extract a substring in Java

6 Answers6