Regex Named Groups in Java

java

regex-patterns

java-7

best-practices

byAlex Kataev·Mar 4, 2025

Utilize (?<name>pattern) for establishing named groups in Java regex. Retrieve them with matcher.group("name"):

Pattern pattern = Pattern.compile("(?<name>\\w+)");
Matcher matcher = pattern.matcher("Alice in wonderland");
if (matcher.find()) {
    // Alice found wondering in a land of code!
    System.out.println(matcher.group("name")); // Outputs: Alice
}

Using this approach, a word is captured as the named group "name" and printed out.

Making the case: When to use named groups

Preferred for enhanced readability and manageability of regex patterns. Particularly handy with multiplex regex groups. Instead of memorizing group order, just call them by names.

Referencing within regex

Use "\k<name>" to refer to a named group within the actual regex pattern:

Pattern pattern = Pattern.compile("(?<word>\\w+)\\s+\\k<word>");
Matcher matcher = pattern.matcher("hello hello");
boolean result = matcher.matches(); // true - whispered hello is heard

String substitution using named groups

Apply "${name}" for referencing named groups during string replacements:

String text = "John Smith";
String replacedText = text.replaceAll("(?<firstName>\\w+) (?<lastName>\\w+)", "${lastName}, ${firstName}");
// The order of the universe restored
System.out.println(replacedText); // Outputs: Smith, John

Traveling back in time: Pre-Java 7

For Java's older versions that lack native regex named group support, turn to third-party libraries like named-regexp or Google's named-regex. These libraries may offer different syntax and limitations compared to Java 7's implementation. They come to the rescue keeping complex patterns in control for Java 5 or 6 bases.

Picking the right library

named-regexp: Compatible with Java 5 and 6, simplifies the experience of taming named groups.
Google's named-regex: An alternative for those dealing with pre-Java 7 times.
jregex: With a risk of not being actively maintained and compatibility issues with Java versions newer than 6, tread with caution.
Regex2: Limited but ready for duty, will serve with certain constraints
Joni: An Oniguruma port, sparingly documented but has named group support.

Conquering the future: Beyond Java 7

Upgrade to Java 7 or above if possible, to leverage the native support for named groups in regex. It's more likely to perform well and receive better support than third-party counterparts.