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Support optional: prefix with logging.log4j2.config.override #44488

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Support optional: prefix with logging.log4j2.config.override #44488

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2 changes: 2 additions & 0 deletions ...boot-project/spring-boot-docs/src/docs/antora/modules/how-to/pages/logging.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -201,3 +201,5 @@ To configure Log4j 2 to use an alternative configuration file format, add the ap
Log4j 2 has support for combining multiple configuration files into a single composite configuration.
To use this support in Spring Boot, configure configprop:logging.log4j2.config.override[] with the locations of one or more secondary configuration files.
The secondary configuration files will be merged with the primary configuration, whether the primary's source is Spring Boot's defaults, a standard location such as `log4j.xml`, or the location configured by the configprop:logging.config[] property.

NOTE: Log4j2 override configuration file locations can be prefixed with `optional:`, for example, `optional:classpath:log4j2-override.xml`, to indicate that the location is optional and should only be loaded if the resource exists.
58 changes: 44 additions & 14 deletions ...pring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java
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Expand Up @@ -16,6 +16,7 @@

package org.springframework.boot.logging.log4j2;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
Expand Down Expand Up @@ -69,6 +70,7 @@
import org.springframework.core.annotation.Order;
import org.springframework.core.env.Environment;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.CollectionUtils;
Expand All @@ -86,6 +88,8 @@
*/
public class Log4J2LoggingSystem extends AbstractLoggingSystem {

private static final String OPTIONAL_PREFIX = "optional:";

private static final String LOG4J_BRIDGE_HANDLER = "org.apache.logging.log4j.jul.Log4jBridgeHandler";

private static final String LOG4J_LOG_MANAGER = "org.apache.logging.log4j.jul.LogManager";
Expand Down Expand Up @@ -270,21 +274,42 @@ protected void loadConfiguration(String location, LogFile logFile, List<String>
try {
List<Configuration> configurations = new ArrayList<>();
LoggerContext context = getLoggerContext();
configurations.add(load(location, context));
ResourceLoader resourceLoader = ApplicationResourceLoader.get();
configurations.add(loadConfiguration(resourceLoader, location, context));
for (String override : overrides) {
configurations.add(load(override, context));
Configuration overrideConfiguration = loadOptionalConfiguration(resourceLoader, override, context);
if (overrideConfiguration != null) {
configurations.add(overrideConfiguration);
}
}
Configuration configuration = (configurations.size() > 1) ? createComposite(configurations)
: configurations.iterator().next();
context.start(configuration);
context.start(createCompositeConfigurationIfNecessary(configurations));
}
catch (Exception ex) {
throw new IllegalStateException("Could not initialize Log4J2 logging from " + location, ex);
}
}

private Configuration load(String location, LoggerContext context) throws IOException {
Resource resource = ApplicationResourceLoader.get().getResource(location);
private Configuration loadOptionalConfiguration(ResourceLoader resourceLoader, String location,
LoggerContext context) throws IOException {
if (location.startsWith(OPTIONAL_PREFIX)) {
Resource resource = resourceLoader.getResource(location.substring(OPTIONAL_PREFIX.length()));
try {
return (resource.exists()) ? loadConfiguration(resource, context) : null;
}
catch (FileNotFoundException ex) {
return null;
}
}
return loadConfiguration(resourceLoader, location, context);
}

private Configuration loadConfiguration(ResourceLoader resourceLoader, String location, LoggerContext context)
throws IOException {
Resource resource = resourceLoader.getResource(location);
return loadConfiguration(resource, context);
}

private Configuration loadConfiguration(Resource resource, LoggerContext context) throws IOException {
ConfigurationFactory factory = ConfigurationFactory.getInstance();
if (resource.isFile()) {
try (InputStream inputStream = resource.getInputStream()) {
Expand All @@ -304,7 +329,10 @@ private Configuration load(String location, LoggerContext context) throws IOExce
}
}

private CompositeConfiguration createComposite(List<Configuration> configurations) {
private Configuration createCompositeConfigurationIfNecessary(List<Configuration> configurations) {
if (configurations.size() == 1) {
return configurations.iterator().next();
}
return new CompositeConfiguration(configurations.stream().map(AbstractConfiguration.class::cast).toList());
}

Expand All @@ -322,19 +350,21 @@ protected void reinitialize(LoggingInitializationContext initializationContext)

private void reinitializeWithOverrides(List<String> overrides) {
LoggerContext context = getLoggerContext();
Configuration base = context.getConfiguration();
List<AbstractConfiguration> configurations = new ArrayList<>();
configurations.add((AbstractConfiguration) base);
List<Configuration> configurations = new ArrayList<>();
configurations.add(context.getConfiguration());
ResourceLoader resourceLoader = ApplicationResourceLoader.get();
for (String override : overrides) {
try {
configurations.add((AbstractConfiguration) load(override, context));
Configuration overrideConfiguration = loadOptionalConfiguration(resourceLoader, override, context);
if (overrideConfiguration != null) {
configurations.add(overrideConfiguration);
}
}
catch (IOException ex) {
throw new RuntimeException("Failed to load overriding configuration from '" + override + "'", ex);
}
}
CompositeConfiguration composite = new CompositeConfiguration(configurations);
context.reconfigure(composite);
context.reconfigure(createCompositeConfigurationIfNecessary(configurations));
}

@Override
Expand Down
43 changes: 43 additions & 0 deletions ...-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemTests.java
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Expand Up @@ -43,6 +43,7 @@
import org.apache.logging.log4j.core.config.Reconfigurable;
import org.apache.logging.log4j.core.config.composite.CompositeConfiguration;
import org.apache.logging.log4j.core.config.plugins.util.PluginRegistry;
import org.apache.logging.log4j.core.config.xml.XmlConfiguration;
import org.apache.logging.log4j.core.util.ShutdownCallbackRegistry;
import org.apache.logging.log4j.jul.Log4jBridgeHandler;
import org.apache.logging.log4j.status.StatusListener;
Expand Down Expand Up @@ -453,6 +454,48 @@ void shutdownHookIsDisabled() {
.isFalse();
}

@Test
@WithNonDefaultXmlResource
void loadOptionalOverrideConfigurationWhenDoesNotExist() {
this.environment.setProperty("logging.log4j2.config.override", "optional:classpath:override.xml");
this.loggingSystem.initialize(this.initializationContext, "classpath:nondefault.xml", null);
assertThat(this.loggingSystem.getConfiguration()).isInstanceOf(XmlConfiguration.class);
}

@Test
void loadOptionalOverrideConfigurationWhenDoesNotExistUponReinitialization() {
this.environment.setProperty("logging.log4j2.config.override", "optional:classpath:override.xml");
this.loggingSystem.beforeInitialize();
this.loggingSystem.initialize(this.initializationContext, null, null);
assertThat(this.loggingSystem.getConfiguration()).isInstanceOf(XmlConfiguration.class);
this.loggingSystem.cleanUp();
this.loggingSystem.beforeInitialize();
this.loggingSystem.initialize(this.initializationContext, null, null);
assertThat(this.loggingSystem.getConfiguration()).isInstanceOf(XmlConfiguration.class);
}

@Test
@WithNonDefaultXmlResource
@WithOverrideXmlResource
void loadOptionalOverrideConfiguration() {
this.environment.setProperty("logging.log4j2.config.override", "optional:classpath:override.xml");
this.loggingSystem.initialize(this.initializationContext, "classpath:nondefault.xml", null);
assertThat(this.loggingSystem.getConfiguration()).isInstanceOf(CompositeConfiguration.class);
}

@Test
@WithOverrideXmlResource
void loadOptionalOverrideConfigurationUponReinitialization() {
this.environment.setProperty("logging.log4j2.config.override", "optional:classpath:override.xml");
this.loggingSystem.beforeInitialize();
this.loggingSystem.initialize(this.initializationContext, null, null);
assertThat(this.loggingSystem.getConfiguration()).isInstanceOf(CompositeConfiguration.class);
this.loggingSystem.cleanUp();
this.loggingSystem.beforeInitialize();
this.loggingSystem.initialize(this.initializationContext, null, null);
assertThat(this.loggingSystem.getConfiguration()).isInstanceOf(CompositeConfiguration.class);
}

@Test
@WithNonDefaultXmlResource
@WithOverrideXmlResource
Expand Down