Question

I have a string that i am trying to extract patterns from, the string is as follows:

(  ELT2N ( ELTOK wpSA910 wpSA909 wpSA908 wpSA474 ) )

The problem is, i dont know how many of the strings beginning with ‘wp’ will be in the string i am trying to search, however i want toi extract all of them using one statement. I am currently using the pattern below:

private final static String STARS_LINE_PATTERN = "\\(\\s+?(\\w+?)\\s+?\\(\\s+(\\w+)\\s+?(\\w+?\\s??){1,}\\s+?\\)\\s+?\\)";

The pattern is matching the string and returning the ‘ELT2N’ and the ‘ELTOK’ strings but is not returning the strings prefixed by ‘wp’.

Can anyone help?

Thanks

Simon

Answer 1

Java regex like most flavors can only keep the last capture when you repeat a capturing group.

For this particular problem, you may want to match the entire wp sequence into one group in one regex, and then post-process it again with another regex. In this case, a simple split is enough.

Here’s a snippet to illustrate the idea:

    import java.util.regex.*;
    import java.util.*;
    //...

    String text = "(  ELT2N ( ELTOK wpSA910 wpSA909 wpSA908 wpSA474 ) )";
    String regex =
        "< (word) < (word) ((?:word )+)> >"
            .replace(" ", "\\s+")
            .replace("<", "\\(")
            .replace(">", "\\)")
            .replace("word", "\\w+");

    Matcher m = Pattern.compile(regex).matcher(text);
    if (m.find()) {
        System.out.printf("%s; %s;%n%s",
            m.group(1),
            m.group(2),
            Arrays.toString(m.group(3).split("\\s+"))
        );
    }

The above prints:

ELT2N; ELTOK;
[wpSA910, wpSA909, wpSA908, wpSA474]

So the entire wp sequence is captured by \3 of the regex pattern, which is then split into its parts.

References

• regular-expressions.info/Repeating a Capturing Group vs Capturing a Repeating Group

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