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

@@ -41,11 +41,14 @@
 import org.springframework.beans.factory.BeanFactoryUtils;
 import org.springframework.beans.factory.ListableBeanFactory;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
+import org.springframework.boot.autoconfigure.AutoConfigurationPackages;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 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.boot.jackson.JsonMixinScanPackages;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -93,6 +96,15 @@ public JsonComponentModule jsonComponentModule() {
 		return new JsonComponentModule();
 	}
 
+	@Bean
+	public JsonMixinModule jsonMixinModule(ApplicationContext context) {
+		List<String> packages = JsonMixinScanPackages.get(context).getPackageNames();
+		if (packages.isEmpty() && AutoConfigurationPackages.has(context)) {
+			packages = AutoConfigurationPackages.get(context);
+		}
+		return new JsonMixinModule(context, packages);
+	}
+
 	@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 +1,59 @@
+/*
+ * 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;
+
+/**
+ * Provides a mixin class implementation that registers with Jackson when using
+ * {@link JsonMixinModule}.
+ *
+ * @author Guirong Hu
+ * @see JsonMixinModule
+ * @since 2.7.0
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+public @interface JsonMixin {
+
+	/**
+	 * Alias for the {@link #type()} attribute. Allows for more concise annotation
+	 * declarations e.g.: {@code @JsonMixin(MyType.class)} instead of
+	 * {@code @JsonMixin(type=MyType.class)}.
+	 * @return the mixed-in classes
+	 * @since 2.7.0
+	 */
+	@AliasFor("type")
+	Class<?>[] value() default {};
+
+	/**
+	 * The types that are handled by the provided mix-in class. {@link #value()} is an
+	 * alias for (and mutually exclusive with) this attribute.
+	 * @return the mixed-in classes
+	 * @since 2.7.0
+	 */
+	@AliasFor("value")
+	Class<?>[] type() default {};
+
+}

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

@@ -0,0 +1,107 @@
+/*
+ * 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.io.IOException;
+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.classreading.MetadataReader;
+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 register {@link JsonMixin @JsonMixin}
+ * annotated beans.
+ *
+ * @author Guirong Hu
+ * @since 2.7.0
+ * @see JsonMixin
+ */
+public class JsonMixinModule extends SimpleModule implements InitializingBean {
+
+	private final ApplicationContext context;
+
+	private final Collection<String> basePackages;
+
+	/**
+	 * Create a new {@link JsonMixinModule} instance.
+	 * @param context the source application context
+	 * @param basePackages the packages to check for annotated classes
+	 */
+	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);
+		Class<?>[] targetTypes = annotation.getClassArray("type");
+		if (ObjectUtils.isEmpty(targetTypes)) {
+			return;
+		}
+		for (Class<?> targetType : targetTypes) {
+			setMixInAnnotation(targetType, mixinClass);
+		}
+	}
+
+	static class JsonMixinComponentScanner extends ClassPathScanningCandidateComponentProvider {
+
+		@Override
+		protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
+			return true;
+		}
+
+		@Override
+		protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
+			return beanDefinition.getMetadata().hasAnnotation(JsonMixin.class.getName());
+		}
+
+	}
+
+}

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

@@ -0,0 +1,75 @@
+/*
+ * 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.context.annotation.Import;
+import org.springframework.core.annotation.AliasFor;
+
+/**
+ * Configures the base packages used by auto-configuration when scanning for mix-in
+ * classes. One of {@link #basePackageClasses()}, {@link #basePackages()} or its alias
+ * {@link #value()} may be specified to define specific packages to scan. If specific
+ * packages are not defined scanning will occur from the package of the class with this
+ * annotation.
+ *
+ * @author Guirong Hu
+ * @since 2.7.0
+ * @see JsonMixinScanPackages
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+@Import(JsonMixinScanPackages.Registrar.class)
+public @interface JsonMixinScan {
+
+	/**
+	 * Alias for the {@link #basePackages()} attribute. Allows for more concise annotation
+	 * declarations e.g.: {@code @JsonMixinScan("org.my.pkg")} instead of
+	 * {@code @JsonMixinScan(basePackages="org.my.pkg")}.
+	 * @return the base packages to scan
+	 */
+	@AliasFor("basePackages")
+	String[] value() default {};
+
+	/**
+	 * Base packages to scan for mix-in classes. {@link #value()} is an alias for (and
+	 * mutually exclusive with) this attribute.
+	 * <p>
+	 * Use {@link #basePackageClasses()} for a type-safe alternative to String-based
+	 * package names.
+	 * @return the base packages to scan
+	 */
+	@AliasFor("value")
+	String[] basePackages() default {};
+
+	/**
+	 * Type-safe alternative to {@link #basePackages()} for specifying the packages to
+	 * scan for mix-in classes. The package of each class specified will be scanned.
+	 * <p>
+	 * Consider creating a special no-op marker class or interface in each package that
+	 * serves no purpose other than being referenced by this attribute.
+	 * @return classes from the base packages to scan
+	 */
+	Class<?>[] basePackageClasses() default {};
+
+}