junit-team/junit5 · error · ExtensionConfigurationException

Could not instantiate TimeZoneProvider because of exception

Error message

Could not instantiate TimeZoneProvider because of exception

What it means

Thrown as ExtensionConfigurationException by DefaultTimeZoneExtension.createTimeZoneFromProvider when ReflectionSupport.newInstance(providerClass) fails while constructing the TimeZoneProvider declared in @DefaultTimeZone(timeZoneProvider = ...). The original exception is attached as the cause. The provider must have an accessible no-arg constructor and must not throw during construction.

Source

Thrown at junit-jupiter-api/src/main/java/org/junit/jupiter/api/util/DefaultTimeZoneExtension.java:98

		TimeZone configuredTimeZone = TimeZone.getTimeZone(timeZoneId);
		// TimeZone::getTimeZone returns with GMT as fallback if the given ID cannot be understood
		if (configuredTimeZone.equals(TimeZone.getTimeZone("GMT")) && !"GMT".equals(timeZoneId)) {
			throw new ExtensionConfigurationException("""
					@DefaultTimeZone not configured correctly.
					Could not find the specified time zone + '%s'.
					Please use correct identifiers, e.g. "GMT" for Greenwich Mean Time.
					""".formatted(timeZoneId));
		}
		return configuredTimeZone;
	}

	private static TimeZone createTimeZoneFromProvider(Class<? extends TimeZoneProvider> providerClass) {
		try {
			TimeZoneProvider provider = ReflectionSupport.newInstance(providerClass);
			return Optional.ofNullable(provider.get()).orElse(TimeZone.getTimeZone("GMT"));
		}
		catch (Exception exception) {
			throw new ExtensionConfigurationException("Could not instantiate TimeZoneProvider because of exception",
				exception);
		}
	}

	@Override
	public void afterEach(ExtensionContext context) {
		load(context, DEFAULT_KEY).ifPresent(TimeZone::setDefault);
	}

	private static void store(ExtensionContext context, String key, TimeZone value) {
		getStore(context).put(key, value);
	}

	private static Optional<TimeZone> load(ExtensionContext context, String key) {
		return Optional.ofNullable(getStore(context).get(key, TimeZone.class));
	}

	private static ExtensionContext.Store getStore(ExtensionContext context) {

View on GitHub (pinned to 956246301e)

Solutions

1. Give the TimeZoneProvider implementation a public no-arg constructor.
2. Make the class concrete and accessible (public, top-level or public static nested).
3. Move fallible initialization out of the constructor into the get() method.
4. Inspect the attached cause exception to pinpoint the construction failure.

Example fix

// before
public class MyTimeZoneProvider implements TimeZoneProvider {
    public MyTimeZoneProvider(Path config) { /* no no-arg ctor */ }
    public TimeZone get() { return TimeZone.getTimeZone("GMT"); }
}

// after
public class MyTimeZoneProvider implements TimeZoneProvider {
    public MyTimeZoneProvider() {}
    public TimeZone get() { return TimeZone.getTimeZone("GMT"); }
}

Class<? extends TimeZoneProvider> c = MyTimeZoneProvider.class;
if (c.isInterface() || Modifier.isAbstract(c.getModifiers()) || !Modifier.isPublic(c.getModifiers())) {
    throw new IllegalStateException("TimeZoneProvider must be a public concrete class");
}
try {
    c.getDeclaredConstructor();
} catch (NoSuchMethodException e) {
    throw new IllegalStateException("TimeZoneProvider needs a public no-arg constructor", e);
}
ReflectionSupport.newInstance(c); // verify ctor does not throw

static boolean isUsableProvider(Class<? extends TimeZoneProvider> c) {
    if (c.isInterface() || Modifier.isAbstract(c.getModifiers())) return false;
    try { c.getDeclaredConstructor(); return true; }
    catch (NoSuchMethodException e) { return false; }
}

When it happens

Trigger: Setting timeZoneProvider to a class lacking a no-arg constructor, an abstract class or interface, a non-public class with an inaccessible constructor, or a class whose constructor throws.

Common situations: Provider class requiring configuration arguments; constructor performing I/O or env access that fails in the test environment; package-private provider used across packages.

Related errors

• LocaleProvider instance could not be constructed because of
• Either a valid time zone id or a TimeZoneProvider must be pr
• @DefaultTimeZone not configured correctly. Could not find th
• This class must not be instantiated
• This class must not be instantiated

AI-assisted analysis of junit-team/junit5@956246301e (2026-08-04). Data as JSON: /data/errors/aefdde5d16858664.json. Report an issue: GitHub.