Replace outcome of JsonMixins scanning in AOT optimized contexts

This commit adds an AOT contribution that replaces the scanning of
@JsonMixin by a mapping in generated code. This makes sure that such
components are found in a native image.

Closes gh-32567

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfiguration.java

@@ -48,6 +48,7 @@ import org.springframework.boot.autoconfigure.jackson.JacksonProperties.Construc
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.jackson.JsonComponentModule;
 import org.springframework.boot.jackson.JsonMixinModule;
+import org.springframework.boot.jackson.JsonMixinModuleEntries;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -95,11 +96,23 @@ public class JacksonAutoConfiguration {
 		return new JsonComponentModule();
 	}
 
-	@Bean
-	public JsonMixinModule jsonMixinModule(ApplicationContext context) {
-		List<String> packages = AutoConfigurationPackages.has(context) ? AutoConfigurationPackages.get(context)
-				: Collections.emptyList();
-		return new JsonMixinModule(context, packages);
+	@Configuration(proxyBeanMethods = false)
+	static class JacksonMixinConfiguration {
+
+		@Bean
+		static JsonMixinModuleEntries jsonMixinModuleEntries(ApplicationContext context) {
+			List<String> packages = AutoConfigurationPackages.has(context) ? AutoConfigurationPackages.get(context)
+					: Collections.emptyList();
+			return JsonMixinModuleEntries.scan(context, packages);
+		}
+
+		@Bean
+		JsonMixinModule jsonMixinModule(ApplicationContext context, JsonMixinModuleEntries entries) {
+			JsonMixinModule jsonMixinModule = new JsonMixinModule();
+			jsonMixinModule.registerEntries(entries, context.getClassLoader());
+			return jsonMixinModule;
+		}
+
 	}
 
 	@Configuration(proxyBeanMethods = false)

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jackson/JacksonAutoConfigurationTests.java

@@ -54,7 +54,9 @@ import org.springframework.boot.autoconfigure.AutoConfigurationPackage;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration;
 import org.springframework.boot.jackson.JsonComponent;
+import org.springframework.boot.jackson.JsonMixin;
 import org.springframework.boot.jackson.JsonMixinModule;
+import org.springframework.boot.jackson.JsonMixinModuleEntries;
 import org.springframework.boot.jackson.JsonObjectSerializer;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
@@ -65,6 +67,7 @@ import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.Assertions.entry;
 import static org.mockito.Mockito.mock;
 
 /**
@@ -96,10 +99,10 @@ class JacksonAutoConfigurationTests {
 	@Test
 	void jsonMixinModuleShouldBeAutoConfiguredWithBasePackages() {
 		this.contextRunner.withUserConfiguration(MixinConfiguration.class).run((context) -> {
-			assertThat(context).hasSingleBean(JsonMixinModule.class);
-			JsonMixinModule module = context.getBean(JsonMixinModule.class);
-			assertThat(module).extracting("basePackages", InstanceOfAssertFactories.list(String.class))
-					.containsExactly(MixinConfiguration.class.getPackage().getName());
+			assertThat(context).hasSingleBean(JsonMixinModule.class).hasSingleBean(JsonMixinModuleEntries.class);
+			JsonMixinModuleEntries moduleEntries = context.getBean(JsonMixinModuleEntries.class);
+			assertThat(moduleEntries).extracting("entries", InstanceOfAssertFactories.MAP)
+					.contains(entry(Person.class, EmptyMixin.class));
 		});
 	}
 
@@ -644,6 +647,11 @@ class JacksonAutoConfigurationTests {
 
 	}
 
+	@JsonMixin(type = Person.class)
+	static class EmptyMixin {
+
+	}
+
 	@AutoConfigurationPackage
 	static class MixinConfiguration {
 

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jackson/JsonMixinModule.java

@@ -21,18 +21,8 @@ import java.util.Collection;
 import com.fasterxml.jackson.databind.Module;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 
-import org.springframework.beans.factory.InitializingBean;
-import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
-import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.context.ApplicationContext;
-import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
-import org.springframework.core.annotation.MergedAnnotation;
-import org.springframework.core.annotation.MergedAnnotations;
-import org.springframework.core.type.filter.AnnotationTypeFilter;
 import org.springframework.util.Assert;
-import org.springframework.util.ClassUtils;
-import org.springframework.util.ObjectUtils;
-import org.springframework.util.StringUtils;
 
 /**
  * Spring Bean and Jackson {@link Module} to find and
@@ -40,62 +30,35 @@ import org.springframework.util.StringUtils;
  * {@link JsonMixin @JsonMixin}-annotated classes.
  *
  * @author Guirong Hu
+ * @author Stephane Nicoll
  * @since 2.7.0
  * @see JsonMixin
  */
-public class JsonMixinModule extends SimpleModule implements InitializingBean {
+public class JsonMixinModule extends SimpleModule {
 
-	private final ApplicationContext context;
-
-	private final Collection<String> basePackages;
+	public JsonMixinModule() {
+	}
 
 	/**
 	 * Create a new {@link JsonMixinModule} instance.
 	 * @param context the source application context
 	 * @param basePackages the packages to check for annotated classes
+	 * @deprecated since 3.0.0 in favor of
+	 * {@link #registerEntries(JsonMixinModuleEntries, ClassLoader)}
 	 */
+	@Deprecated(since = "3.0.0", forRemoval = true)
 	public JsonMixinModule(ApplicationContext context, Collection<String> basePackages) {
 		Assert.notNull(context, "Context must not be null");
-		this.context = context;
-		this.basePackages = basePackages;
-	}
-
-	@Override
-	public void afterPropertiesSet() throws Exception {
-		if (ObjectUtils.isEmpty(this.basePackages)) {
-			return;
-		}
-		JsonMixinComponentScanner scanner = new JsonMixinComponentScanner();
-		scanner.setEnvironment(this.context.getEnvironment());
-		scanner.setResourceLoader(this.context);
-		for (String basePackage : this.basePackages) {
-			if (StringUtils.hasText(basePackage)) {
-				for (BeanDefinition candidate : scanner.findCandidateComponents(basePackage)) {
-					addJsonMixin(ClassUtils.forName(candidate.getBeanClassName(), this.context.getClassLoader()));
-				}
-			}
-		}
-	}
-
-	private void addJsonMixin(Class<?> mixinClass) {
-		MergedAnnotation<JsonMixin> annotation = MergedAnnotations
-				.from(mixinClass, MergedAnnotations.SearchStrategy.TYPE_HIERARCHY).get(JsonMixin.class);
-		for (Class<?> targetType : annotation.getClassArray("type")) {
-			setMixInAnnotation(targetType, mixinClass);
-		}
+		registerEntries(JsonMixinModuleEntries.scan(context, basePackages), context.getClassLoader());
 	}
 
-	static class JsonMixinComponentScanner extends ClassPathScanningCandidateComponentProvider {
-
-		JsonMixinComponentScanner() {
-			addIncludeFilter(new AnnotationTypeFilter(JsonMixin.class));
-		}
-
-		@Override
-		protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
-			return true;
-		}
-
+	/**
+	 * Register the specified {@link JsonMixinModuleEntries entries}.
+	 * @param entries the entries to register to this instance
+	 * @param classLoader the classloader to use
+	 */
+	public void registerEntries(JsonMixinModuleEntries entries, ClassLoader classLoader) {
+		entries.doWithEntry(classLoader, this::setMixInAnnotation);
 	}
 
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jackson/JsonMixinModuleEntries.java

@@ -0,0 +1,164 @@
+/*
+ * Copyright 2012-2022 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.jackson;
+
+import java.util.Collection;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+
+import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
+import org.springframework.beans.factory.config.BeanDefinition;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
+import org.springframework.core.annotation.MergedAnnotation;
+import org.springframework.core.annotation.MergedAnnotations;
+import org.springframework.core.type.filter.AnnotationTypeFilter;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.ObjectUtils;
+import org.springframework.util.StringUtils;
+
+/**
+ * Provide the mapping of json mixin class to consider.
+ *
+ * @author Stephane Nicoll
+ * @since 3.0.0
+ */
+public final class JsonMixinModuleEntries {
+
+	private final Map<Object, Object> entries;
+
+	private JsonMixinModuleEntries(Builder builder) {
+		this.entries = new LinkedHashMap<>(builder.entries);
+	}
+
+	/**
+	 * Create an instance using the specified {@link Builder}.
+	 * @param mixins a consumer of the builder
+	 * @return an instance with the state of the customized builder.
+	 */
+	public static JsonMixinModuleEntries create(Consumer<Builder> mixins) {
+		Builder builder = new Builder();
+		mixins.accept(builder);
+		return builder.build();
+	}
+
+	/**
+	 * Scan the classpath for {@link JsonMixin @JsonMixin} in the specified
+	 * {@code basePackages}.
+	 * @param context the application context to use
+	 * @param basePackages the base packages to consider
+	 * @return an instance with the result of the scanning
+	 */
+	public static JsonMixinModuleEntries scan(ApplicationContext context, Collection<String> basePackages) {
+		return JsonMixinModuleEntries.create((builder) -> {
+			if (ObjectUtils.isEmpty(basePackages)) {
+				return;
+			}
+			JsonMixinComponentScanner scanner = new JsonMixinComponentScanner();
+			scanner.setEnvironment(context.getEnvironment());
+			scanner.setResourceLoader(context);
+			for (String basePackage : basePackages) {
+				if (StringUtils.hasText(basePackage)) {
+					for (BeanDefinition candidate : scanner.findCandidateComponents(basePackage)) {
+						Class<?> mixinClass = ClassUtils.resolveClassName(candidate.getBeanClassName(),
+								context.getClassLoader());
+						registerMixinClass(builder, mixinClass);
+					}
+				}
+			}
+		});
+	}
+
+	private static void registerMixinClass(Builder builder, Class<?> mixinClass) {
+		MergedAnnotation<JsonMixin> annotation = MergedAnnotations
+				.from(mixinClass, MergedAnnotations.SearchStrategy.TYPE_HIERARCHY).get(JsonMixin.class);
+		for (Class<?> targetType : annotation.getClassArray("type")) {
+			builder.and(targetType, mixinClass);
+		}
+
+	}
+
+	/**
+	 * Perform an action on each entry defined by this instance. If a class needs to be
+	 * resolved from its class name, the specified {@link ClassLoader} is used.
+	 * @param classLoader the classloader to use to resolve class name if necessary
+	 * @param action the action to invoke on each type to mixin class entry
+	 */
+	public void doWithEntry(ClassLoader classLoader, BiConsumer<Class<?>, Class<?>> action) {
+		this.entries.forEach((type, mixin) -> action.accept(resolveClassNameIfNecessary(type, classLoader),
+				resolveClassNameIfNecessary(mixin, classLoader)));
+	}
+
+	private Class<?> resolveClassNameIfNecessary(Object type, ClassLoader classLoader) {
+		return (type instanceof Class<?> clazz) ? clazz : ClassUtils.resolveClassName((String) type, classLoader);
+	}
+
+	/**
+	 * Builder for {@link JsonMixinModuleEntries}.
+	 */
+	public static class Builder {
+
+		private final Map<Object, Object> entries;
+
+		Builder() {
+			this.entries = new LinkedHashMap<>();
+		}
+
+		/**
+		 * Add a mapping for the specified class names.
+		 * @param typeClassName the type class name
+		 * @param mixinClassName the mixin class name
+		 * @return {@code this}, to facilitate method chaining
+		 */
+		public Builder and(String typeClassName, String mixinClassName) {
+			this.entries.put(typeClassName, mixinClassName);
+			return this;
+		}
+
+		/**
+		 * Add a mapping for the specified classes.
+		 * @param type the type class
+		 * @param mixinClass the mixin class
+		 * @return {@code this}, to facilitate method chaining
+		 */
+		public Builder and(Class<?> type, Class<?> mixinClass) {
+			this.entries.put(type, mixinClass);
+			return this;
+		}
+
+		JsonMixinModuleEntries build() {
+			return new JsonMixinModuleEntries(this);
+		}
+
+	}
+
+	static class JsonMixinComponentScanner extends ClassPathScanningCandidateComponentProvider {
+
+		JsonMixinComponentScanner() {
+			addIncludeFilter(new AnnotationTypeFilter(JsonMixin.class));
+		}
+
+		@Override
+		protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
+			return true;
+		}
+
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jackson/JsonMixinModuleEntriesBeanRegistrationAotProcessor.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2012-2022 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.jackson;
+
+import java.lang.reflect.Executable;
+import java.util.LinkedHashSet;
+import java.util.Set;
+
+import javax.lang.model.element.Modifier;
+
+import org.springframework.aot.generate.AccessControl;
+import org.springframework.aot.generate.GeneratedMethod;
+import org.springframework.aot.generate.GenerationContext;
+import org.springframework.aot.hint.BindingReflectionHintsRegistrar;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.beans.factory.aot.BeanRegistrationAotContribution;
+import org.springframework.beans.factory.aot.BeanRegistrationAotProcessor;
+import org.springframework.beans.factory.aot.BeanRegistrationCode;
+import org.springframework.beans.factory.aot.BeanRegistrationCodeFragments;
+import org.springframework.beans.factory.aot.BeanRegistrationCodeFragmentsDecorator;
+import org.springframework.beans.factory.support.RegisteredBean;
+import org.springframework.javapoet.CodeBlock;
+
+/**
+ * {@link BeanRegistrationAotProcessor} that replaces any {@link JsonMixinModuleEntries}
+ * by an hard-coded equivalent. This has the effect of disabling scanning at runtime.
+ *
+ * @author Stephane Nicoll
+ */
+class JsonMixinModuleEntriesBeanRegistrationAotProcessor implements BeanRegistrationAotProcessor {
+
+	@Override
+	public BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
+		if (registeredBean.getBeanClass().equals(JsonMixinModuleEntries.class)) {
+			return BeanRegistrationAotContribution
+					.withCustomCodeFragments((codeFragments) -> new AotContribution(codeFragments, registeredBean));
+		}
+		return null;
+	}
+
+	static class AotContribution extends BeanRegistrationCodeFragmentsDecorator {
+
+		private final RegisteredBean registeredBean;
+
+		private final ClassLoader classLoader;
+
+		AotContribution(BeanRegistrationCodeFragments delegate, RegisteredBean registeredBean) {
+			super(delegate);
+			this.registeredBean = registeredBean;
+			this.classLoader = registeredBean.getBeanFactory().getBeanClassLoader();
+		}
+
+		@Override
+		public CodeBlock generateInstanceSupplierCode(GenerationContext generationContext,
+				BeanRegistrationCode beanRegistrationCode, Executable constructorOrFactoryMethod,
+				boolean allowDirectSupplierShortcut) {
+			JsonMixinModuleEntries entries = this.registeredBean.getBeanFactory()
+					.getBean(this.registeredBean.getBeanName(), JsonMixinModuleEntries.class);
+			contributeHints(generationContext.getRuntimeHints(), entries);
+			GeneratedMethod generatedMethod = beanRegistrationCode.getMethods().add("getInstance", (method) -> {
+				Class<?> beanType = JsonMixinModuleEntries.class;
+				method.addJavadoc("Get the bean instance for '$L'.", this.registeredBean.getBeanName());
+				method.addModifiers(Modifier.PRIVATE, Modifier.STATIC);
+				method.returns(beanType);
+				CodeBlock.Builder code = CodeBlock.builder();
+				code.add("return $T.create(", JsonMixinModuleEntries.class).beginControlFlow("(mixins) ->");
+				entries.doWithEntry(this.classLoader, (type, mixin) -> addEntryCode(code, type, mixin));
+				code.endControlFlow(")");
+				method.addCode(code.build());
+			});
+			return generatedMethod.toMethodReference().toCodeBlock();
+		}
+
+		private void addEntryCode(CodeBlock.Builder code, Class<?> type, Class<?> mixin) {
+			AccessControl accessForTypes = AccessControl.lowest(AccessControl.forClass(type),
+					AccessControl.forClass(mixin));
+			if (accessForTypes.isPublic()) {
+				code.addStatement("$L.and($T.class, $T.class)", "mixins", type, mixin);
+			}
+			else {
+				code.addStatement("$L.and($S, $S)", "mixins", type.getName(), mixin.getName());
+			}
+		}
+
+		private void contributeHints(RuntimeHints runtimeHints, JsonMixinModuleEntries entries) {
+			Set<Class<?>> mixins = new LinkedHashSet<>();
+			entries.doWithEntry(this.classLoader, (type, mixin) -> mixins.add(type));
+			new BindingReflectionHintsRegistrar().registerReflectionHints(runtimeHints.reflection(),
+					mixins.toArray(Class<?>[]::new));
+		}
+
+	}
+
+}

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

@@ -13,4 +13,5 @@ org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor=\
 org.springframework.boot.context.properties.ConfigurationPropertiesBeanFactoryInitializationAotProcessor
 
 org.springframework.beans.factory.aot.BeanRegistrationAotProcessor=\
-org.springframework.boot.context.properties.ConfigurationPropertiesBeanRegistrationAotProcessor
+org.springframework.boot.context.properties.ConfigurationPropertiesBeanRegistrationAotProcessor,\
+org.springframework.boot.jackson.JsonMixinModuleEntriesBeanRegistrationAotProcessor

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jackson/JsonMixinModuleEntriesBeanRegistrationAotProcessorTests.java

@@ -0,0 +1,139 @@
+/*
+ * Copyright 2012-2022 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.jackson;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.function.BiConsumer;
+
+import org.assertj.core.api.InstanceOfAssertFactories;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.predicate.RuntimeHintsPredicates;
+import org.springframework.aot.test.generate.TestGenerationContext;
+import org.springframework.beans.factory.support.BeanDefinitionBuilder;
+import org.springframework.boot.jackson.scan.a.RenameMixInClass;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationContextInitializer;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.aot.ApplicationContextAotGenerator;
+import org.springframework.context.support.GenericApplicationContext;
+import org.springframework.core.test.tools.CompileWithForkedClassLoader;
+import org.springframework.core.test.tools.Compiled;
+import org.springframework.core.test.tools.TestCompiler;
+import org.springframework.javapoet.ClassName;
+import org.springframework.util.ClassUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.entry;
+
+/**
+ * Tests for {@link JsonMixinModuleEntriesBeanRegistrationAotProcessor}.
+ *
+ * @author Stephane Nicoll
+ */
+@CompileWithForkedClassLoader
+class JsonMixinModuleEntriesBeanRegistrationAotProcessorTests {
+
+	private final TestGenerationContext generationContext = new TestGenerationContext();
+
+	private final GenericApplicationContext applicationContext = new AnnotationConfigApplicationContext();
+
+	@Test
+	void processAheadOfTimeShouldRegisterBindingHintsForMixins() {
+		registerEntries(RenameMixInClass.class);
+		processAheadOfTime();
+		RuntimeHints runtimeHints = this.generationContext.getRuntimeHints();
+		assertThat(RuntimeHintsPredicates.reflection().onMethod(Name.class, "getName")).accepts(runtimeHints);
+		assertThat(RuntimeHintsPredicates.reflection().onMethod(NameAndAge.class, "getAge")).accepts(runtimeHints);
+	}
+
+	@Test
+	void processAheadOfTimeWhenPublicClassShouldRegisterClass() {
+		registerEntries(RenameMixInClass.class);
+		compile((freshContext, compiled) -> {
+			assertThat(freshContext.getBean(TestConfiguration.class).scanningInvoked).isFalse();
+			JsonMixinModuleEntries jsonMixinModuleEntries = freshContext.getBean(JsonMixinModuleEntries.class);
+			assertThat(jsonMixinModuleEntries).extracting("entries", InstanceOfAssertFactories.MAP).containsExactly(
+					entry(Name.class, RenameMixInClass.class), entry(NameAndAge.class, RenameMixInClass.class));
+		});
+	}
+
+	@Test
+	void processAheadOfTimeWhenNonAccessibleClassShouldRegisterClassName() {
+		Class<?> privateMixinClass = ClassUtils
+				.resolveClassName("org.springframework.boot.jackson.scan.e.PrivateMixInClass", null);
+		registerEntries(privateMixinClass);
+		compile((freshContext, compiled) -> {
+			assertThat(freshContext.getBean(TestConfiguration.class).scanningInvoked).isFalse();
+			JsonMixinModuleEntries jsonMixinModuleEntries = freshContext.getBean(JsonMixinModuleEntries.class);
+			assertThat(jsonMixinModuleEntries).extracting("entries", InstanceOfAssertFactories.MAP).containsExactly(
+					entry(Name.class.getName(), privateMixinClass.getName()),
+					entry(NameAndAge.class.getName(), privateMixinClass.getName()));
+		});
+	}
+
+	private ClassName processAheadOfTime() {
+		ClassName className = new ApplicationContextAotGenerator().processAheadOfTime(this.applicationContext,
+				this.generationContext);
+		this.generationContext.writeGeneratedContent();
+		return className;
+	}
+
+	@SuppressWarnings("unchecked")
+	private void compile(BiConsumer<GenericApplicationContext, Compiled> result) {
+		ClassName className = processAheadOfTime();
+		TestCompiler.forSystem().with(this.generationContext).compile((compiled) -> {
+			GenericApplicationContext freshApplicationContext = new GenericApplicationContext();
+			ApplicationContextInitializer<GenericApplicationContext> initializer = compiled
+					.getInstance(ApplicationContextInitializer.class, className.toString());
+			initializer.initialize(freshApplicationContext);
+			freshApplicationContext.refresh();
+			result.accept(freshApplicationContext, compiled);
+		});
+	}
+
+	private void registerEntries(Class<?>... basePackageClasses) {
+		List<String> packageNames = Arrays.stream(basePackageClasses).map(Class::getPackageName).toList();
+		this.applicationContext.registerBeanDefinition("configuration", BeanDefinitionBuilder
+				.rootBeanDefinition(TestConfiguration.class).addConstructorArgValue(packageNames).getBeanDefinition());
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class TestConfiguration {
+
+		public boolean scanningInvoked;
+
+		private final Collection<String> packageNames;
+
+		TestConfiguration(Collection<String> packageNames) {
+			this.packageNames = packageNames;
+		}
+
+		@Bean
+		JsonMixinModuleEntries jsonMixinModuleEntries(ApplicationContext applicationContext) {
+			this.scanningInvoked = true;
+			return JsonMixinModuleEntries.scan(applicationContext, this.packageNames);
+		}
+
+	}
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jackson/JsonMixinModuleTests.java

@@ -52,6 +52,8 @@ class JsonMixinModuleTests {
 	}
 
 	@Test
+	@Deprecated(since = "3.0.0", forRemoval = true)
+	@SuppressWarnings("removal")
 	void createWhenContextIsNullShouldThrowException() {
 		assertThatIllegalArgumentException().isThrownBy(() -> new JsonMixinModule(null, Collections.emptyList()))
 				.withMessageContaining("Context must not be null");
@@ -89,12 +91,20 @@ class JsonMixinModuleTests {
 
 	private void load(Class<?>... basePackageClasses) {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
-		List<String> basePackages = Arrays.stream(basePackageClasses).map(ClassUtils::getPackageName).toList();
-		context.registerBean(JsonMixinModule.class, () -> new JsonMixinModule(context, basePackages));
+		context.registerBean(JsonMixinModule.class, () -> createJsonMixinModule(context, basePackageClasses));
 		context.refresh();
 		this.context = context;
 	}
 
+	private JsonMixinModule createJsonMixinModule(AnnotationConfigApplicationContext context,
+			Class<?>... basePackageClasses) {
+		List<String> basePackages = Arrays.stream(basePackageClasses).map(ClassUtils::getPackageName).toList();
+		JsonMixinModuleEntries entries = JsonMixinModuleEntries.scan(context, basePackages);
+		JsonMixinModule jsonMixinModule = new JsonMixinModule();
+		jsonMixinModule.registerEntries(entries, context.getClassLoader());
+		return jsonMixinModule;
+	}
+
 	private void assertMixIn(Module module, Name value, String expectedJson) throws Exception {
 		ObjectMapper mapper = new ObjectMapper();
 		mapper.registerModule(module);

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jackson/scan/e/PrivateMixInClass.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2012-2022 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.jackson.scan.e;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import org.springframework.boot.jackson.JsonMixin;
+import org.springframework.boot.jackson.Name;
+import org.springframework.boot.jackson.NameAndAge;
+
+@JsonMixin(type = { Name.class, NameAndAge.class })
+class PrivateMixInClass {
+
+	@JsonProperty("username")
+	String getName() {
+		return null;
+	}
+
+}