What causes "Unable to parse version: " in apache/maven?

Trim and reject empty/uninterpolated ('${...}') strings before parsing

apache/maven · error · VersionParserException

Unable to parse version:

Error message

Unable to parse version:

What it means

DefaultModelVersionParser's DefaultVersion wraps the resolver VersionScheme; parsing a version string that the scheme rejects throws VersionParserException('Unable to parse version: <input>'). The generic parse is used when a raw string (e.g. from a POM property or plugin parameter) must become a Version object, and the underlying scheme (typically GenericVersionScheme) rejects malformed input such as empty strings.

Source

Thrown at impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultModelVersionParser.java:90

        requireNonNull(constraint, "constraint");
        return new DefaultVersionConstraint(versionScheme, constraint);
    }

    static class DefaultVersion implements Version {
        private final VersionScheme versionScheme;
        private final org.eclipse.aether.version.Version delegate;

        DefaultVersion(VersionScheme versionScheme, org.eclipse.aether.version.Version delegate) {
            this.versionScheme = versionScheme;
            this.delegate = delegate;
        }

        DefaultVersion(VersionScheme versionScheme, String delegateValue) {
            this.versionScheme = versionScheme;
            try {
                this.delegate = versionScheme.parseVersion(delegateValue);
            } catch (InvalidVersionSpecificationException e) {
                throw new VersionParserException("Unable to parse version: " + delegateValue, e);
            }
        }

        @Override
        public int compareTo(Version o) {
            if (o instanceof DefaultVersion defaultVersion) {
                return delegate.compareTo(defaultVersion.delegate);
            } else {
                return compareTo(new DefaultVersion(versionScheme, o.toString()));
            }
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {

View on GitHub (pinned to e4093d4e12)

Solutions

Trim and reject empty/uninterpolated ('${...}') strings before parsing
Catch VersionParserException and report which string failed with the POM/location context
Where possible use versionScheme.parseVersion indirectly through Model API which surfaces better diagnostics

Example fix

// before
Version v = session.getService(VersionParser.class).parseVersion(props.getProperty('project.version'));

// after
String raw = props.getProperty('project.version');
if (raw == null || raw.isBlank() || raw.contains('${')) {
    throw new IllegalArgumentException('project.version not interpolated: ' + raw);
}
Version v = session.getService(VersionParser.class).parseVersion(raw.trim());

Defensive patterns

Strategy: try-catch

Validate before calling

if (version == null || version.isBlank() || version.contains('${')) {
    throw new IllegalArgumentException('Version string is blank or uninterpolated: ' + version);
}

Try / catch

try {
    Version v = parser.parseVersion(raw);
} catch (VersionParserException e) {
    throw new IllegalArgumentException('Bad version "' + raw + '" in ' + source, e);
}

Prevention

Trim version strings and reject blanks/uninterpolated properties
Carry the POM location/context in wrapped errors for diagnosability
Prefer comparing already-parsed Version objects over re-parsing strings

When it happens

Trigger: session.getService(VersionParser.class).parseVersion(''), parseVersion('${some.unset.property}'), or a version string with characters the version scheme cannot tokenize; also compareTo on a foreign Version implementation that re-parses its toString().

Common situations: POM properties for versions left uninterpolated; user input or CLI args (-Dversion=...) passed to version comparisons; empty default version strings in code; version strings with stray whitespace.

Understand the failure class

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/4226f54b2e63203c. Report an issue: GitHub.