Add AOT runtime hints for Log4j Core 2

core/spring-boot/build.gradle

@@ -69,6 +69,9 @@ dependencies {
 	testImplementation("org.hibernate.validator:hibernate-validator")
 	testImplementation("org.jboss.logging:jboss-logging")
 	testImplementation("org.springframework.data:spring-data-r2dbc")
+
+	// Used in Log4J2RuntimeHintsTests
+	testRuntimeOnly("com.fasterxml.jackson.dataformat:jackson-dataformat-yaml")
 }
 
 def syncJavaTemplates = tasks.register("syncJavaTemplates", Sync) {

core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java

@@ -89,10 +89,6 @@ 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";
-
 	private static final SpringEnvironmentPropertySource propertySource = new SpringEnvironmentPropertySource();
 
 	static final String ENVIRONMENT_KEY = Conventions.getQualifiedAttributeName(Log4J2LoggingSystem.class,
@@ -123,18 +119,18 @@ public Log4J2LoggingSystem(ClassLoader classLoader) {
 	protected String[] getStandardConfigLocations() {
 		List<String> locations = new ArrayList<>();
 		locations.add("log4j2-test.properties");
-		if (isClassAvailable("com.fasterxml.jackson.dataformat.yaml.YAMLParser")) {
+		if (isClassAvailable(Log4J2RuntimeHints.YAML_TREE_PARSER_V2)) {
 			Collections.addAll(locations, "log4j2-test.yaml", "log4j2-test.yml");
 		}
-		if (isClassAvailable("com.fasterxml.jackson.databind.ObjectMapper")) {
+		if (isClassAvailable(Log4J2RuntimeHints.JSON_TREE_PARSER_V2)) {
 			Collections.addAll(locations, "log4j2-test.json", "log4j2-test.jsn");
 		}
 		locations.add("log4j2-test.xml");
 		locations.add("log4j2.properties");
-		if (isClassAvailable("com.fasterxml.jackson.dataformat.yaml.YAMLParser")) {
+		if (isClassAvailable(Log4J2RuntimeHints.YAML_TREE_PARSER_V2)) {
 			Collections.addAll(locations, "log4j2.yaml", "log4j2.yml");
 		}
-		if (isClassAvailable("com.fasterxml.jackson.databind.ObjectMapper")) {
+		if (isClassAvailable(Log4J2RuntimeHints.JSON_TREE_PARSER_V2)) {
 			Collections.addAll(locations, "log4j2.json", "log4j2.jsn");
 		}
 		locations.add("log4j2.xml");
@@ -185,11 +181,11 @@ private boolean isJulUsingASingleConsoleHandlerAtMost() {
 
 	private boolean isLog4jLogManagerInstalled() {
 		final String logManagerClassName = java.util.logging.LogManager.getLogManager().getClass().getName();
-		return LOG4J_LOG_MANAGER.equals(logManagerClassName);
+		return Log4J2RuntimeHints.LOG4J_LOG_MANAGER.equals(logManagerClassName);
 	}
 
 	private boolean isLog4jBridgeHandlerAvailable() {
-		return ClassUtils.isPresent(LOG4J_BRIDGE_HANDLER, getClassLoader());
+		return ClassUtils.isPresent(Log4J2RuntimeHints.LOG4J_BRIDGE_HANDLER, getClassLoader());
 	}
 
 	private void removeLog4jBridgeHandler() {

core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2RuntimeHints.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2025-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.logging.log4j2;
+
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.RuntimeHintsRegistrar;
+import org.springframework.util.ClassUtils;
+
+/**
+ * {@link RuntimeHintsRegistrar} implementation for {@link Log4J2LoggingSystem}.
+ *
+ * @author Piotr P. Karwasz
+ */
+class Log4J2RuntimeHints implements RuntimeHintsRegistrar {
+
+	// Log4j2LoggingSystem checks for the presence of these classes reflectively.
+	static final String PROVIDER = "org.apache.logging.log4j.core.impl.Log4jProvider";
+
+	// Tree parsers used by Log4j 2 for configuration files.
+	static final String JSON_TREE_PARSER_V2 = "com.fasterxml.jackson.databind.ObjectMapper";
+	static final String YAML_TREE_PARSER_V2 = "com.fasterxml.jackson.dataformat.yaml.YAMLMapper";
+
+	// JUL implementations that use Log4j 2 API.
+	static final String LOG4J_BRIDGE_HANDLER = "org.apache.logging.log4j.jul.Log4jBridgeHandler";
+	static final String LOG4J_LOG_MANAGER = "org.apache.logging.log4j.jul.LogManager";
+
+	@Override
+	public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+		if (!ClassUtils.isPresent(PROVIDER, classLoader)) {
+			return;
+		}
+		registerTypeForReachability(hints, classLoader, PROVIDER);
+		// Register default Log4j2 configuration files
+		hints.resources().registerPattern("org/springframework/boot/logging/log4j2/log4j2.xml");
+		hints.resources().registerPattern("org/springframework/boot/logging/log4j2/log4j2-file.xml");
+		hints.resources().registerPattern("log4j2.springboot");
+		// Declares the types that Log4j2LoggingSystem checks for existence reflectively.
+		registerTypeForReachability(hints, classLoader, JSON_TREE_PARSER_V2);
+		registerTypeForReachability(hints, classLoader, YAML_TREE_PARSER_V2);
+		registerTypeForReachability(hints, classLoader, LOG4J_BRIDGE_HANDLER);
+		registerTypeForReachability(hints, classLoader, LOG4J_LOG_MANAGER);
+		// Don't need to register the custom Log4j 2 plugins,
+		// since they will be registered by the Log4j 2 `GraalvmPluginProcessor`.
+	}
+
+	/**
+	 * Registers the type to prevent GraalVM from removing it during the native build.
+	 * @param hints the runtime hints to register with
+	 * @param classLoader the class loader to use for type resolution
+	 * @param typeName the name of the type to register
+	 */
+	private void registerTypeForReachability(RuntimeHints hints, ClassLoader classLoader, String typeName) {
+		hints.reflection().registerTypeIfPresent(classLoader, typeName);
+	}
+
+}

core/spring-boot/src/main/resources/META-INF/spring/aot.factories

@@ -7,6 +7,7 @@ org.springframework.boot.context.config.ConfigDataPropertiesRuntimeHints,\
 org.springframework.boot.env.PropertySourceRuntimeHints,\
 org.springframework.boot.json.JacksonRuntimeHints,\
 org.springframework.boot.logging.java.JavaLoggingSystemRuntimeHints,\
+org.springframework.boot.logging.log4j2.Log4J2RuntimeHints,\
 org.springframework.boot.logging.logback.LogbackRuntimeHints,\
 org.springframework.boot.logging.structured.ElasticCommonSchemaProperties$ElasticCommonSchemaPropertiesRuntimeHints,\
 org.springframework.boot.logging.structured.GraylogExtendedLogFormatProperties$GraylogExtendedLogFormatPropertiesRuntimeHints,\

core/spring-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemTests.java

@@ -309,15 +309,15 @@ void configLocationsWithJacksonDatabind() {
 
 	@Test
 	void configLocationsWithJacksonDataformatYaml() {
-		this.loggingSystem.availableClasses("com.fasterxml.jackson.dataformat.yaml.YAMLParser");
+		this.loggingSystem.availableClasses("com.fasterxml.jackson.dataformat.yaml.YAMLMapper");
 		assertThat(this.loggingSystem.getStandardConfigLocations()).containsExactly("log4j2-test.properties",
 				"log4j2-test.yaml", "log4j2-test.yml", "log4j2-test.xml", "log4j2.properties", "log4j2.yaml",
 				"log4j2.yml", "log4j2.xml");
 	}
 
 	@Test
 	void configLocationsWithJacksonDatabindAndDataformatYaml() {
-		this.loggingSystem.availableClasses("com.fasterxml.jackson.dataformat.yaml.YAMLParser",
+		this.loggingSystem.availableClasses("com.fasterxml.jackson.dataformat.yaml.YAMLMapper",
 				ObjectMapper.class.getName());
 		assertThat(this.loggingSystem.getStandardConfigLocations()).containsExactly("log4j2-test.properties",
 				"log4j2-test.yaml", "log4j2-test.yml", "log4j2-test.json", "log4j2-test.jsn", "log4j2-test.xml",

core/spring-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2RuntimeHintsTests.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2012-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.logging.log4j2;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.apache.logging.log4j.core.impl.Log4jProvider;
+import org.apache.logging.log4j.jul.Log4jBridgeHandler;
+import org.apache.logging.log4j.jul.LogManager;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aot.hint.ReflectionHints;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.TypeReference;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link Log4J2RuntimeHints}.
+ *
+ * @author Piotr P. Karwasz
+ */
+class Log4J2RuntimeHintsTests {
+
+	@Test
+	void registersHintsForTypesCheckedByLog4J2LoggingSystem() {
+		ReflectionHints reflection = registerHints();
+		assertThat(reflection.getTypeHint(Log4jProvider.class)).isNotNull();
+		assertThat(reflection.getTypeHint(Log4jBridgeHandler.class)).isNotNull();
+		assertThat(reflection.getTypeHint(LogManager.class)).isNotNull();
+	}
+
+	@Test
+	void registersHintsForConfigurationFileParsers() {
+		ReflectionHints reflection = registerHints();
+		// JSON
+		assertThat(reflection.getTypeHint(ObjectMapper.class)).isNotNull();
+		// YAML
+		assertThat(reflection.getTypeHint(TypeReference.of("com.fasterxml.jackson.dataformat.yaml.YAMLMapper")))
+			.isNotNull();
+	}
+
+	@Test
+	void doesNotRegisterHintsWhenLog4jCoreIsNotAvailable() {
+		RuntimeHints hints = new RuntimeHints();
+		new Log4J2RuntimeHints().registerHints(hints, ClassLoader.getPlatformClassLoader());
+		assertThat(hints.reflection().typeHints()).isEmpty();
+	}
+
+	private ReflectionHints registerHints() {
+		RuntimeHints hints = new RuntimeHints();
+		new Log4J2RuntimeHints().registerHints(hints, getClass().getClassLoader());
+		return hints.reflection();
+	}
+
+}