Simplify registration of Jackson mixin types

Closes gh-25920

Author: terminux

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

@@ -46,6 +46,7 @@
 import org.springframework.boot.autoconfigure.jackson.JacksonProperties.ConstructorDetectorStrategy;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.jackson.JsonComponentModule;
+import org.springframework.boot.jackson.JsonMixinModule;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -93,6 +94,11 @@ public JsonComponentModule jsonComponentModule() {
 		return new JsonComponentModule();
 	}
 
+	@Bean
+	public JsonMixinModule jsonMixinModule() {
+		return new JsonMixinModule();
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(Jackson2ObjectMapperBuilder.class)
 	static class JacksonObjectMapperConfiguration {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * 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.
@@ -52,6 +52,7 @@
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration;
 import org.springframework.boot.jackson.JsonComponent;
+import org.springframework.boot.jackson.JsonMixinModule;
 import org.springframework.boot.jackson.JsonObjectSerializer;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
@@ -90,6 +91,11 @@ void doubleModuleRegistration() {
 				});
 	}
 
+	@Test
+	void jsonMixinModuleShouldBeAutoconfigured() {
+		this.contextRunner.run((context) -> assertThat(context).hasSingleBean(JsonMixinModule.class));
+	}
+
 	@Test
 	void noCustomDateFormat() {
 		this.contextRunner.run((context) -> {

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

@@ -0,0 +1,58 @@
+/*
+ * 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.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.core.annotation.AliasFor;
+import org.springframework.stereotype.Component;
+
+/**
+ * {@link Component @Component} that provides mix-in class implementations to be
+ * registered with Jackson when {@link JsonMixinModule} is in use.
+ *
+ * @author Guirong Hu
+ * @see JsonMixinModule
+ * @since 2.7.0
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+@Component
+public @interface JsonMixin {
+
+	/**
+	 * Explicitly specify the name of the Spring bean definition associated with the
+	 * {@code @JsonMixin} class. If left unspecified (the common case), a bean name will
+	 * be automatically generated.
+	 * @return the explicit component name, if any (or empty String otherwise)
+	 */
+	@AliasFor(annotation = Component.class)
+	String value() default "";
+
+	/**
+	 * The types that are handled by the provided mix-in class.
+	 * @return the types that should be mixed-in by the component
+	 * @since 2.7.0
+	 */
+	Class<?>[] type() default {};
+
+}

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

@@ -0,0 +1,83 @@
+/*
+ * 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.Map;
+
+import com.fasterxml.jackson.databind.Module;
+import com.fasterxml.jackson.databind.module.SimpleModule;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.BeanFactory;
+import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.beans.factory.HierarchicalBeanFactory;
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.beans.factory.ListableBeanFactory;
+import org.springframework.core.annotation.MergedAnnotation;
+import org.springframework.core.annotation.MergedAnnotations;
+import org.springframework.util.ObjectUtils;
+
+/**
+ * Spring Bean and Jackson {@link Module} to register {@link JsonMixin @JsonMixin}
+ * annotated beans.
+ *
+ * @author Guirong Hu
+ * @since 2.7.0
+ * @see JsonMixin
+ */
+public class JsonMixinModule extends SimpleModule implements BeanFactoryAware, InitializingBean {
+
+	private BeanFactory beanFactory;
+
+	@Override
+	public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
+		this.beanFactory = beanFactory;
+	}
+
+	@Override
+	public void afterPropertiesSet() throws Exception {
+		BeanFactory beanFactory = this.beanFactory;
+		while (beanFactory != null) {
+			if (beanFactory instanceof ListableBeanFactory) {
+				addJsonMixinBeans((ListableBeanFactory) beanFactory);
+			}
+			beanFactory = (beanFactory instanceof HierarchicalBeanFactory)
+					? ((HierarchicalBeanFactory) beanFactory).getParentBeanFactory() : null;
+		}
+	}
+
+	private void addJsonMixinBeans(ListableBeanFactory beanFactory) {
+		Map<String, Object> beans = beanFactory.getBeansWithAnnotation(JsonMixin.class);
+		for (Object bean : beans.values()) {
+			addJsonMixinBean(bean);
+		}
+	}
+
+	private void addJsonMixinBean(Object bean) {
+		Class<?> mixinClass = bean.getClass();
+		MergedAnnotation<JsonMixin> annotation = MergedAnnotations
+				.from(mixinClass, MergedAnnotations.SearchStrategy.TYPE_HIERARCHY).get(JsonMixin.class);
+		Class<?>[] targetTypes = annotation.getClassArray("type");
+		if (ObjectUtils.isEmpty(targetTypes)) {
+			return;
+		}
+		for (Class<?> targetType : targetTypes) {
+			setMixInAnnotation(targetType, mixinClass);
+		}
+	}
+
+}

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

@@ -0,0 +1,124 @@
+/*
+ * 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 com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.databind.Module;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Lookup;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link JsonMixinModule}.
+ *
+ * @author Guirong Hu
+ */
+public class JsonMixinModuleTests {
+
+	private AnnotationConfigApplicationContext context;
+
+	@AfterEach
+	void closeContext() {
+		if (this.context != null) {
+			this.context.close();
+		}
+	}
+
+	@Test
+	void jsonWithModuleWithRenameMixInClassShouldBeMixedIn() throws Exception {
+		load(RenameMixInClass.class);
+		JsonMixinModule module = this.context.getBean(JsonMixinModule.class);
+		assertMixIn(module, new Name("spring"), "{\"username\":\"spring\"}");
+		assertMixIn(module, new NameAndAge("spring", 100), "{\"age\":100,\"username\":\"spring\"}");
+	}
+
+	@Test
+	void jsonWithModuleWithEmptyMixInClassShouldNotBeMixedIn() throws Exception {
+		load(EmptyMixInClass.class);
+		JsonMixinModule module = this.context.getBean(JsonMixinModule.class);
+		assertMixIn(module, new Name("spring"), "{\"name\":\"spring\"}");
+		assertMixIn(module, new NameAndAge("spring", 100), "{\"name\":\"spring\",\"age\":100}");
+	}
+
+	@Test
+	void jsonWithModuleWithRenameAndContainsLookupMethodMixInAbstractClassShouldBeMixedIn() throws Exception {
+		load(RenameAndContainsLookupMethodMixInAbstractClass.class);
+		JsonMixinModule module = this.context.getBean(JsonMixinModule.class);
+		assertMixIn(module, new NameAndAge("spring", 100), "{\"age\":100,\"username\":\"spring\"}");
+	}
+
+	@Test
+	void jsonWithModuleWithRenameAndContainsLookupMethodMixInInterfaceShouldBeMixedIn() throws Exception {
+		load(RenameAndContainsLookupMethodMixInInterface.class);
+		JsonMixinModule module = this.context.getBean(JsonMixinModule.class);
+		assertMixIn(module, new NameAndAge("spring", 100), "{\"age\":100,\"username\":\"spring\"}");
+	}
+
+	private void load(Class<?>... configs) {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+		context.register(configs);
+		context.register(JsonMixinModule.class);
+		context.refresh();
+		this.context = context;
+	}
+
+	private void assertMixIn(Module module, Name value, String expectedJson) throws Exception {
+		ObjectMapper mapper = new ObjectMapper();
+		mapper.registerModule(module);
+		String json = mapper.writeValueAsString(value);
+		assertThat(json).isEqualToIgnoringWhitespace(expectedJson);
+	}
+
+	@JsonMixin(type = { Name.class, NameAndAge.class })
+	static class RenameMixInClass {
+
+		@JsonProperty("username")
+		String getName() {
+			return null;
+		}
+
+	}
+
+	@JsonMixin(type = NameAndAge.class)
+	abstract static class RenameAndContainsLookupMethodMixInAbstractClass {
+
+		@JsonProperty("username")
+		@Lookup
+		abstract String getName();
+
+	}
+
+	@JsonMixin(type = NameAndAge.class)
+	interface RenameAndContainsLookupMethodMixInInterface {
+
+		@JsonProperty("username")
+		@Lookup
+		String getName();
+
+	}
+
+	@JsonMixin(type = { Name.class, NameAndAge.class })
+	static class EmptyMixInClass {
+
+	}
+
+}