Extracting segments of a semver version string via Java regex

Issue

Java 8 here. I am trying to parse a semver (or at least, my flavor of semver) string and extract out its main segments:

• Major version number
• Minor version number
• Patch number
• Qualifier (RC, SNAPSHOT, RELEASE, etc.)

Here is my code:

String version = "1.0.1-RC";
Pattern versionPattern = Pattern.compile("^[1-9]\\d*\\.\\d+\\.\\d+(?:-[a-zA-Z0-9]+)?$");
Matcher matcher = versionPattern.matcher(version);

if (matcher.matches()) {

    System.out.println("\n\n\matching version is: " + matcher.group(0));
    System.out.println("\nmajor #: " + matcher.group(1));
    System.out.println("\nminor #: " + matcher.group(2));
    System.out.println("\npatch #: " + matcher.group(3));
    System.out.println("\nqualifier: " + matcher.group(4) + "\n\n\n");

}

When this runs, I get the following output on the console:

matching version is: 1.0.1-RC
2019-10-18 14:32:05,952 [main] 84b37cef-70f9-4ab8-bafb-005821699766 ERROR c.s.f.s.listeners.StartupListener - java.lang.IndexOutOfBoundsException: No group 1

What do I need to do to my regex and/our use of the Matcher API so that I can extract:

• 1 as the major number
• 0 as the minor number
• 1 as the patch number
• RC as the qualifier

Any ideas?

Solution

NOTE:

• You should not escape m in a string literal, \m is not a valid string escape sequence and the code won't compile
• Matcher#matches() requires a full string match, no need to add ^ and $ anchors
• To be able to reference Matcher#group(n), you need to define the groups in the pattern in the first place. Wrap the parts you need with pairs of unescaped parentheses.

Use

String version = "1.0.1-RC";
Pattern versionPattern = Pattern.compile("([1-9]\\d*)\\.(\\d+)\\.(\\d+)(?:-([a-zA-Z0-9]+))?");
Matcher matcher = versionPattern.matcher(version);

if (matcher.matches()) {
    System.out.println("matching version is: " + matcher.group(0));
    System.out.println("major #: " + matcher.group(1));
    System.out.println("minor #: " + matcher.group(2));
    System.out.println("patch #: " + matcher.group(3));
    System.out.println("qualifier: " + matcher.group(4) + "\n\n\n");
}

See the Java demo, output:

matching version is: 1.0.1-RC
major #: 1
minor #: 0
patch #: 1
qualifier: RC

Answered By - Wiktor Stribiżew