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Add AOT runtime hints for Log4j Core 2
This change introduces AOT runtime hints for Log4j Core 2 to support its integration with Spring Boot native images. Starting with version `2.25.0`, Log4j Core 2 includes built-in GraalVM reachability metadata, allowing native image generation without requiring additional manual configuration. This contribution complements that by adding Spring Boot–specific metadata: * Registers default Spring Boot configuration files. * Registers classes referenced via `ClassUtils.isPresent(...)` checks. Fixes #42273. > [!NOTE] > This change should be reviewed in conjunction with #46334, which configures Log4j Core’s `GraalVmProcessor` to generate reachability metadata for Spring Boot’s custom Log4j plugins. Signed-off-by: Piotr P. Karwasz <piotr@github.copernik.eu>
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‎core/spring-boot/build.gradle‎

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@@ -71,6 +71,9 @@ dependencies {
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testImplementation("org.hibernate.validator:hibernate-validator")
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testImplementation("org.jboss.logging:jboss-logging")
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testImplementation("org.springframework.data:spring-data-r2dbc")
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// Used in Log4J2RuntimeHintsTests
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testRuntimeOnly("com.fasterxml.jackson.dataformat:jackson-dataformat-yaml")
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}
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def syncJavaTemplates = tasks.register("syncJavaTemplates", Sync) {

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

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@@ -90,44 +90,50 @@ public class Log4J2LoggingSystem extends AbstractLoggingSystem {
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private static final String OPTIONAL_PREFIX = "optional:";
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private static final String LOG4J_BRIDGE_HANDLER = "org.apache.logging.log4j.jul.Log4jBridgeHandler";
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/**
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* JUL handler that routes messages to the Log4j API (optional dependency).
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*/
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static final String LOG4J_BRIDGE_HANDLER = "org.apache.logging.log4j.jul.Log4jBridgeHandler";
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private static final String LOG4J_LOG_MANAGER = "org.apache.logging.log4j.jul.LogManager";
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/**
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* JUL LogManager that routes messages to the Log4j API as the backend.
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*/
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static final String LOG4J_LOG_MANAGER = "org.apache.logging.log4j.jul.LogManager";
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/**
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* JSON tree parser used by Log4j 2 (optional dependency).
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*/
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private static final String JSON_TREE_PARSER_V2 = "com.fasterxml.jackson.databind.ObjectMapper";
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static final String JSON_TREE_PARSER_V2 = "com.fasterxml.jackson.databind.ObjectMapper";
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/**
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* JSON tree parser embedded in Log4j 3.
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*/
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private static final String JSON_TREE_PARSER_V3 = "org.apache.logging.log4j.kit.json.JsonReader";
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static final String JSON_TREE_PARSER_V3 = "org.apache.logging.log4j.kit.json.JsonReader";
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/**
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* Configuration factory for properties files (Log4j 2).
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*/
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private static final String PROPS_CONFIGURATION_FACTORY_V2 = "org.apache.logging.log4j.core.config.properties.PropertiesConfigurationFactory";
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static final String PROPS_CONFIGURATION_FACTORY_V2 = "org.apache.logging.log4j.core.config.properties.PropertiesConfigurationFactory";
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/**
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* Configuration factory for properties files (Log4j 3, optional dependency).
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*/
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private static final String PROPS_CONFIGURATION_FACTORY_V3 = "org.apache.logging.log4j.config.properties.JavaPropsConfigurationFactory";
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static final String PROPS_CONFIGURATION_FACTORY_V3 = "org.apache.logging.log4j.config.properties.JavaPropsConfigurationFactory";
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/**
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* YAML tree parser used by Log4j 2 (optional dependency).
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*/
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private static final String YAML_TREE_PARSER_V2 = "com.fasterxml.jackson.dataformat.yaml.YAMLMapper";
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static final String YAML_TREE_PARSER_V2 = "com.fasterxml.jackson.dataformat.yaml.YAMLMapper";
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/**
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* Configuration factory for YAML files (Log4j 2, embedded).
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*/
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private static final String YAML_CONFIGURATION_FACTORY_V2 = "org.apache.logging.log4j.core.config.yaml.YamlConfigurationFactory";
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static final String YAML_CONFIGURATION_FACTORY_V2 = "org.apache.logging.log4j.core.config.yaml.YamlConfigurationFactory";
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/**
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* Configuration factory for YAML files (Log4j 3, optional dependency).
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*/
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private static final String YAML_CONFIGURATION_FACTORY_V3 = "org.apache.logging.log4j.config.yaml.YamlConfigurationFactory";
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static final String YAML_CONFIGURATION_FACTORY_V3 = "org.apache.logging.log4j.config.yaml.YamlConfigurationFactory";
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private static final SpringEnvironmentPropertySource propertySource = new SpringEnvironmentPropertySource();
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@@ -616,8 +622,10 @@ protected String getDefaultLogCorrelationPattern() {
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@Order(0)
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public static class Factory implements LoggingSystemFactory {
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private static final boolean PRESENT = ClassUtils
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.isPresent("org.apache.logging.log4j.core.impl.Log4jContextFactory", Factory.class.getClassLoader());
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static final String LOG4J_CORE_CONTEXT_FACTORY = "org.apache.logging.log4j.core.impl.Log4jContextFactory";
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private static final boolean PRESENT = ClassUtils.isPresent(LOG4J_CORE_CONTEXT_FACTORY,
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Factory.class.getClassLoader());
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@Override
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public @Nullable LoggingSystem getLoggingSystem(ClassLoader classLoader) {

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

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/*
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* Copyright 2025-present the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.springframework.boot.logging.log4j2;
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import org.jspecify.annotations.Nullable;
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import org.springframework.aot.hint.RuntimeHints;
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import org.springframework.aot.hint.RuntimeHintsRegistrar;
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import org.springframework.util.ClassUtils;
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/**
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* {@link RuntimeHintsRegistrar} implementation for {@link Log4J2LoggingSystem}.
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*
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* @author Piotr P. Karwasz
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*/
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class Log4J2RuntimeHints implements RuntimeHintsRegistrar {
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@Override
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public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
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if (!ClassUtils.isPresent(Log4J2LoggingSystem.Factory.LOG4J_CORE_CONTEXT_FACTORY, classLoader)) {
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return;
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}
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.Factory.LOG4J_CORE_CONTEXT_FACTORY);
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// Register default Log4j2 configuration files
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hints.resources().registerPattern("org/springframework/boot/logging/log4j2/log4j2.xml");
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hints.resources().registerPattern("org/springframework/boot/logging/log4j2/log4j2-file.xml");
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hints.resources().registerPattern("log4j2.springboot");
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// Declares the types that Log4j2LoggingSystem checks for existence reflectively.
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.JSON_TREE_PARSER_V2);
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.JSON_TREE_PARSER_V3);
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.PROPS_CONFIGURATION_FACTORY_V2);
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.PROPS_CONFIGURATION_FACTORY_V3);
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.YAML_TREE_PARSER_V2);
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.YAML_CONFIGURATION_FACTORY_V2);
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.YAML_CONFIGURATION_FACTORY_V3);
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// Register JUL to Log4j 2 bridge handler
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.LOG4J_BRIDGE_HANDLER);
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registerTypeForReachability(hints, classLoader, Log4J2LoggingSystem.LOG4J_LOG_MANAGER);
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// Don't need to register the custom Log4j 2 plugins,
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// since they will be registered by the Log4j 2 `GraalvmPluginProcessor`.
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}
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/**
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* Registers the type to prevent GraalVM from removing it during the native build.
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* @param hints the runtime hints to register with
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* @param classLoader the class loader to use for type resolution
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* @param typeName the name of the type to register
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*/
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private void registerTypeForReachability(RuntimeHints hints, @Nullable ClassLoader classLoader, String typeName) {
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hints.reflection().registerTypeIfPresent(classLoader, typeName);
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}
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}

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

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

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

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/*
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* Copyright 2012-present the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.springframework.boot.logging.log4j2;
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import org.apache.logging.log4j.core.impl.Log4jContextFactory;
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import org.apache.logging.log4j.jul.Log4jBridgeHandler;
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import org.apache.logging.log4j.jul.LogManager;
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import org.junit.jupiter.api.Test;
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import org.springframework.aot.hint.ReflectionHints;
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import org.springframework.aot.hint.RuntimeHints;
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import org.springframework.aot.hint.TypeReference;
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import static org.assertj.core.api.Assertions.assertThat;
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/**
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* Tests for {@link Log4J2RuntimeHints}.
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*
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* @author Piotr P. Karwasz
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*/
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class Log4J2RuntimeHintsTests {
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@Test
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void registersHintsForTypesCheckedByLog4J2LoggingSystem() {
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ReflectionHints reflection = registerHints();
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// Once Log4j Core is reachable, GraalVM will automatically
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// add reachability metadata embedded in the Log4j Core jar and extensions.
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assertThat(reflection.getTypeHint(Log4jContextFactory.class)).isNotNull();
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assertThat(reflection.getTypeHint(Log4jBridgeHandler.class)).isNotNull();
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assertThat(reflection.getTypeHint(LogManager.class)).isNotNull();
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}
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/**
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*
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*/
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@Test
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void registersHintsForConfigurationFileParsers() {
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ReflectionHints reflection = registerHints();
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// JSON
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assertThat(reflection.getTypeHint(TypeReference.of("com.fasterxml.jackson.databind.ObjectMapper"))).isNotNull();
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// YAML
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assertThat(reflection.getTypeHint(TypeReference.of("com.fasterxml.jackson.dataformat.yaml.YAMLMapper")))
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.isNotNull();
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}
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@Test
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void doesNotRegisterHintsWhenLog4jCoreIsNotAvailable() {
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RuntimeHints hints = new RuntimeHints();
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new Log4J2RuntimeHints().registerHints(hints, ClassLoader.getPlatformClassLoader());
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assertThat(hints.reflection().typeHints()).isEmpty();
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}
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private ReflectionHints registerHints() {
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RuntimeHints hints = new RuntimeHints();
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new Log4J2RuntimeHints().registerHints(hints, getClass().getClassLoader());
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return hints.reflection();
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}
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}

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