RegEx to read multiple parameters of unknown multiplicity

Question

I'm a little stuck at a regular expression. Consider following code:

    String regFlagMulti = "^(\\[([\\w=]*?)\\])*?$";
    String flagMulti = "[TestFlag=1000][TestFlagSecond=1000]";
    Matcher mFlagMulti = Pattern.compile(regFlagMulti).matcher(flagMulti);

    if(mFlagMulti.matches()){
        for(int i = 0; i <= mFlagMulti.groupCount(); i++){
            System.out.println(mFlagMulti.group(i));
        }
    }else{
        System.out.println("MultiFlag didn't match!");
    }

What I want is a regular pattern that gives me the text inside the [ ]; each one in a group of the resulting Matcher object.

Important: I don't know how many [ ] expressions are inside the input string!

For the code above it outputs:

[TestFlag=1000][TestFlagSecond=1000]
[TestFlagSecond=1000]
TestFlagSecond=1000

I can't get the regular Pattern to work. Anyone an idea?

This is not on point, but instead of `([\\w=]*?)`, perhaps `([^\\]]*)` would do as well. — Ted Hopp, May 26 '11 at 13:11

score 3 · Answer 1 · answered May 26 '11 at 13:05

3

Use a pattern which matches a single item in the string and use Matcher.find() to iterate over the whole String.

answered May 26 '11 at 13:05

Aaron Digulla

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score 3 · Accepted Answer · edited May 23 '17 at 12:18

What i want is a regular pattern that gives me the text inside the [ ]; each one in a group of the resulting Matcher object.

Unfortunately this can't be done with the Java regex engine. See my (similar) question over here:

Regular expression with variable number of groups?

This group:

(\\[([\\w=]*?)\\])*
\________________/

is group number 1 and will always contain the last match for that group.

Here's a suggestion for a solution, that also fetches the key/vals:

String regFlagMulti = "(\\[(\\w*?)=(.*?)\\])";
String flagMulti = "[TestFlag=1000][TestFlagSecond=1000]";
Matcher mFlagMulti = Pattern.compile(regFlagMulti).matcher(flagMulti);

while (mFlagMulti.find()) {
    System.out.println("String: " + mFlagMulti.group(1));
    System.out.println("   key: " + mFlagMulti.group(2));
    System.out.println("   val: " + mFlagMulti.group(3));
    System.out.println();
}

Output:

String: [TestFlag=1000]
   key: TestFlag
   val: 1000

String: [TestFlagSecond=1000]
   key: TestFlagSecond
   val: 1000

score 3 · Answer 3 · answered May 26 '11 at 13:08

You can try the following:

String regFlagMulti = "\\[(\\w+=.*?)\\]";
String flagMulti = "[TestFlag=1000][TestFlagSecond=1000]";
Matcher mFlagMulti = Pattern.compile(regFlagMulti).matcher(flagMulti);
while(mFlagMulti.find()){
    System.out.println(mFlagMulti.group(1));
}

Output:

TestFlag=1000
TestFlagSecond=1000

score 0 · Answer 4 · answered May 26 '11 at 13:11

As Aaron correctly pointed out, use one group (they are static to the pattern, repetitions are not added as additional groups) and call find.

The pattern to use could be like this: \G\[([^\]]*)\](?=\[|$)

Group 1 will then contain the text inside the [].

Notes:

\G continues the match where the last match ended

(?= is a positive lookahead to make sure that the end of the pattern is as expected (e.g. either the end of the string, or the next [).

RegEx to read multiple parameters of unknown multiplicity

4 Answers4