Thanks for the review, @vy. I've updated the PR.

If this looks good, I'll proceed with adding tests and changelog.

If this looks good, I'll proceed with adding tests and changelog.

@yybmion, yes, please proceed with tests and a changelog.

@yybmion, yes, please proceed with tests and a changelog.

@vy , Added tests and changelog as requested.

Thanks for the review @vy, Changes applied as requested.

Added a null element check in the URI list to throw a ConfigurationException when any element is null. This ensures that testGetConfigurationWithNullInList passes.

for (final URI uri : uris) {

     if (uri == null) {
          throw new ConfigurationException("URI list contains null element");
   }
...

Job	Requested goals	Build Tool Version	Build Outcome	Build Scan®
build-macos-latest	clean install	3.9.8	✅
build-ubuntu-latest	clean install	3.9.8	✅
build-windows-latest	clean install	3.9.8	✅

Generated by gradle/develocity-actions

@vy, I'm sorry about the confusion. Previously, I bumped the versions of those packages in the last PR (#3839) after making some changes, but I forgot to revert them. I've now restored them to their original values.

@yybmion, CI builds are failing. Would you mind reading the Log4j Development Guide and resolving all build failures, please?

@yybmion, just a sec, why do we need these version bumps? We did not touch to these packages.

@vy I think the version bumps are actually needed because the new public method in ConfigurationFactory is inherited by all its subclasses (JsonConfigurationFactory, XmlConfigurationFactory, etc.), which adds the method to those packages' public API.

This is causing the build failure. I've updated the versions back to 2.26.0.

I realize my comments go a bit beyond the immediate scope of this PR, but the section of code below has become a real maintenance headache. It would be great if we could take the opportunity to clean it up once and for all:

Hi @vy and @ppkarwasz,

Thanks for the feedback! Before I finalize this PR, I'd like to clarify the scope of follow-up work.

Based on the discussion, I see two distinct improvement areas:

1. Factory refactoring (removing duplicate code)

I realize my comments go a bit beyond the immediate scope of this PR, but the section of code below has become a real maintenance headache. It would be great if we could take the opportunity to clean it up once and for all:

logging-log4j2/log4j-core/src/main/java/org/apache/logging/log4j/core/config/ConfigurationFactory.java

Lines 373 to 478 in 8a3fb53

	public Configuration getConfiguration(
	final LoggerContext loggerContext, final String name, final URI configLocation) {
	if (configLocation == null) {
	final String configLocationStr = this.substitutor.replace(
	PropertiesUtil.getProperties().getStringProperty(CONFIGURATION_FILE_PROPERTY));
	if (configLocationStr != null) {
	final String[] sources = parseConfigLocations(configLocationStr);
	if (sources.length > 1) {
	final List<AbstractConfiguration> configs = new ArrayList<>();
	for (final String sourceLocation : sources) {
	final Configuration config = getConfiguration(loggerContext, sourceLocation.trim());
	if (config != null) {
	if (config instanceof AbstractConfiguration) {
	configs.add((AbstractConfiguration) config);
	} else {
	LOGGER.error("Failed to created configuration at {}", sourceLocation);
	return null;
	}
	} else {
	LOGGER.warn("Unable to create configuration for {}, ignoring", sourceLocation);
	}
	}
	if (configs.size() > 1) {
	return new CompositeConfiguration(configs);
	} else if (configs.size() == 1) {
	return configs.get(0);
	}
	}
	return getConfiguration(loggerContext, configLocationStr);
	}
	final String log4j1ConfigStr = this.substitutor.replace(
	PropertiesUtil.getProperties().getStringProperty(LOG4J1_CONFIGURATION_FILE_PROPERTY));
	if (log4j1ConfigStr != null) {
	System.setProperty(LOG4J1_EXPERIMENTAL, "true");
	return getConfiguration(LOG4J1_VERSION, loggerContext, log4j1ConfigStr);
	}
	for (final ConfigurationFactory factory : getFactories()) {
	final String[] types = factory.getSupportedTypes();
	if (types != null) {
	for (final String type : types) {
	if (type.equals(ALL_TYPES)) {
	final Configuration config =
	factory.getConfiguration(loggerContext, name, configLocation);
	if (config != null) {
	return config;
	}
	}
	}
	}
	}
	} else {
	final String[] sources = parseConfigLocations(configLocation);
	if (sources.length > 1) {
	final List<AbstractConfiguration> configs = new ArrayList<>();
	for (final String sourceLocation : sources) {
	final Configuration config = getConfiguration(loggerContext, sourceLocation.trim());
	if (config instanceof AbstractConfiguration) {
	configs.add((AbstractConfiguration) config);
	} else {
	LOGGER.error("Failed to created configuration at {}", sourceLocation);
	return null;
	}
	}
	return new CompositeConfiguration(configs);
	}
	// configLocation != null
	final String configLocationStr = configLocation.toString();
	for (final ConfigurationFactory factory : getFactories()) {
	final String[] types = factory.getSupportedTypes();
	if (types != null) {
	for (final String type : types) {
	if (type.equals(ALL_TYPES) || configLocationStr.endsWith(type)) {
	final Configuration config =
	factory.getConfiguration(loggerContext, name, configLocation);
	if (config != null) {
	return config;
	}
	}
	}
	}
	}
	}
	Configuration config = getConfiguration(loggerContext, true, name);
	if (config == null) {
	config = getConfiguration(loggerContext, true, null);
	if (config == null) {
	config = getConfiguration(loggerContext, false, name);
	if (config == null) {
	config = getConfiguration(loggerContext, false, null);
	}
	}
	}
	if (config != null) {
	return config;
	}
	LOGGER.warn(
	"No Log4j 2 configuration file found. "
	+ "Using default configuration (logging only errors to the console), "
	+ "or user programmatically provided configurations. "
	+ "Set system property 'log4j2.debug' "
	+ "to show Log4j 2 internal initialization logging. "
	+ "See https://logging.apache.org/log4j/2.x/manual/configuration.html for instructions on how to configure Log4j 2");
	return new DefaultConfiguration();
	}

Delegate composite configuration logic in Factory.getConfiguration(ctx, name, URI) to the new getConfiguration(ctx, name, List<URI>) method.

2. Exception-throwing consistency

@yybmion, would you be interested in implementing changes necessary to make other ConfigurationFactory::getConfiguration methods throw on failure too?

Align all getConfiguration methods to throw exceptions instead of returning null

I'm currently working on two changes. Should I handle them in separate PRs?

@ppkarwasz, I've addressed all your remarks. Unless you have more, would you mind approving the PR, please?

@yybmion, you've done a great job in this PR, nothing else is needed from your side. 💯 When this PR gets merged, please submit another one addressing the newly created #3958.