Using Java to find substring of a bigger string us

Question

If I have a string like this:

FOO[BAR]

I need a generic way to get the "BAR" string out of the string so that no matter what string is between the square brackets it would be able to get the string.

e.g.

FOO[DOG] = DOG
FOO[CAT] = CAT

Answer 1

the non-regex way:

String input = "FOO[BAR]", extracted;
extracted = input.substring(input.indexOf("["),input.indexOf("]"));

alternatively, for slightly better performance/memory usage (thanks Hosam):

String input = "FOO[BAR]", extracted;
extracted = input.substring(input.indexOf('['),input.lastIndexOf(']'));

Answer 2

I think your regular expression would look like:

/FOO\[(.+)\]/

Assuming that FOO going to be constant.

So, to put this in Java:

Pattern p = Pattern.compile("FOO\\[(.+)\\]");
Matcher m = p.matcher(inputLine);

Answer 3

String input = "FOO[BAR]";
String result = input.substring(input.indexOf("[")+1,input.lastIndexOf("]"));

This will return the value between first '[' and last ']'

Foo[Bar] => Bar

Foo[Bar[test]] => Bar[test]

Note: You should add error checking if the input string is not well formed.

Answer 4

This is a working example :

RegexpExample.java

package org.regexp.replace;

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexpExample
{
    public static void main(String[] args)
    {
        String string = "var1[value1], var2[value2], var3[value3]";
        Pattern pattern = Pattern.compile("(\\[)(.*?)(\\])");
        Matcher matcher = pattern.matcher(string);

        List<String> listMatches = new ArrayList<String>();

        while(matcher.find())
        {
            listMatches.add(matcher.group(2));
        }

        for(String s : listMatches)
        {
            System.out.println(s);
        }
    }
}

It displays :

value1
value2
value3

Answer 5

I'd define that I want a maximum number of non-] characters between [ and ]. These need to be escaped with backslashes (and in Java, these need to be escaped again), and the definition of non-] is a character class, thus inside [ and ] (i.e. [^\\]]). The result:

FOO\\[([^\\]]+)\\]

Answer 6

You should be able to use non-greedy quantifiers, specifically *?. You're going to probably want the following:

Pattern MY_PATTERN = Pattern.compile("\\[(.*?)\\]");

This will give you a pattern that will match your string and put the text within the square brackets in the first group. Have a look at the Pattern API Documentation for more information.

To extract the string, you could use something like the following:

Matcher m = MY_PATTERN.matcher("FOO[BAR]");
while (m.find()) {
    String s = m.group(1);
    // s now contains "BAR"
}