Merge pull request #30152 from terminux

* gh-30152:
  Polish
  Simplify registration of Jackson mixin types

Closes gh-30152

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

@@ -41,11 +41,13 @@ import org.springframework.beans.BeanUtils;
 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.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -93,6 +95,13 @@ 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)
 	@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.
@@ -47,11 +47,14 @@ import com.fasterxml.jackson.databind.exc.InvalidFormatException;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 import com.fasterxml.jackson.databind.util.StdDateFormat;
 import com.fasterxml.jackson.module.paramnames.ParameterNamesModule;
+import org.assertj.core.api.InstanceOfAssertFactories;
 import org.junit.jupiter.api.Test;
 
+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.JsonMixinModule;
 import org.springframework.boot.jackson.JsonObjectSerializer;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
@@ -90,6 +93,16 @@ 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());
+		});
+	}
+
 	@Test
 	void noCustomDateFormat() {
 		this.contextRunner.run((context) -> {
@@ -631,4 +644,9 @@ class JacksonAutoConfigurationTests {
 
 	}
 
+	@AutoConfigurationPackage
+	static class MixinConfiguration {
+
+	}
+
 }

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/json.adoc

@@ -40,6 +40,14 @@ include::code:object/MyJsonComponent[]
 
 
 
+[[features.json.jackson.mixins]]
+==== Mixins
+Jackson has support for mixins that can be used to mix additional annotations into those already declared on a target class.
+Spring Boot's Jackson auto-configuration will scan your application's packages for classes annotated with `@JsonMixin` and register them with the auto-configured `ObjectMapper`.
+The registration is performed by Spring Boot's `JsonMixinModule`.
+
+
+
 [[features.json.gson]]
 === Gson
 Auto-configuration for Gson is provided.

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 +1,101 @@
+/*
+ * 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 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
+ * {@link SimpleModule#setMixInAnnotation(Class, Class) register}
+ * {@link JsonMixin @JsonMixin}-annotated classes.
+ *
+ * @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);
+		for (Class<?> targetType : annotation.getClassArray("type")) {
+			setMixInAnnotation(targetType, mixinClass);
+		}
+	}
+
+	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/test/java/org/springframework/boot/jackson/JsonMixinModuleTests.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.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+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.boot.jackson.scan.a.RenameMixInClass;
+import org.springframework.boot.jackson.scan.b.RenameMixInAbstractClass;
+import org.springframework.boot.jackson.scan.c.RenameMixInInterface;
+import org.springframework.boot.jackson.scan.d.EmptyMixInClass;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.util.ClassUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link JsonMixinModule}.
+ *
+ * @author Guirong Hu
+ */
+class JsonMixinModuleTests {
+
+	private AnnotationConfigApplicationContext context;
+
+	@AfterEach
+	void closeContext() {
+		if (this.context != null) {
+			this.context.close();
+		}
+	}
+
+	@Test
+	void createWhenContextIsNullShouldThrowException() {
+		assertThatIllegalArgumentException().isThrownBy(() -> new JsonMixinModule(null, Collections.emptyList()))
+				.withMessageContaining("Context must not be null");
+	}
+
+	@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 jsonWithModuleWithRenameMixInAbstractClassShouldBeMixedIn() throws Exception {
+		load(RenameMixInAbstractClass.class);
+		JsonMixinModule module = this.context.getBean(JsonMixinModule.class);
+		assertMixIn(module, new NameAndAge("spring", 100), "{\"age\":100,\"username\":\"spring\"}");
+	}
+
+	@Test
+	void jsonWithModuleWithRenameMixInInterfaceShouldBeMixedIn() throws Exception {
+		load(RenameMixInInterface.class);
+		JsonMixinModule module = this.context.getBean(JsonMixinModule.class);
+		assertMixIn(module, new NameAndAge("spring", 100), "{\"age\":100,\"username\":\"spring\"}");
+	}
+
+	private void load(Class<?>... basePackageClasses) {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+		List<String> basePackages = Arrays.stream(basePackageClasses).map(ClassUtils::getPackageName)
+				.collect(Collectors.toList());
+		context.registerBean(JsonMixinModule.class, () -> new JsonMixinModule(context, basePackages));
+		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);
+	}
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jackson/scan/a/RenameMixInClass.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.a;
+
+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 })
+public class RenameMixInClass {
+
+	@JsonProperty("username")
+	String getName() {
+		return null;
+	}
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jackson/scan/b/RenameMixInAbstractClass.java

@@ -0,0 +1,30 @@
+/*
+ * 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.b;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import org.springframework.boot.jackson.JsonMixin;
+import org.springframework.boot.jackson.NameAndAge;
+
+@JsonMixin(type = NameAndAge.class)
+public abstract class RenameMixInAbstractClass {
+
+	@JsonProperty("username")
+	abstract String getName();
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jackson/scan/c/RenameMixInInterface.java

@@ -0,0 +1,30 @@
+/*
+ * 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.c;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import org.springframework.boot.jackson.JsonMixin;
+import org.springframework.boot.jackson.NameAndAge;
+
+@JsonMixin(type = NameAndAge.class)
+public interface RenameMixInInterface {
+
+	@JsonProperty("username")
+	String getName();
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jackson/scan/d/EmptyMixInClass.java

@@ -0,0 +1,26 @@
+/*
+ * 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.d;
+
+import org.springframework.boot.jackson.JsonMixin;
+import org.springframework.boot.jackson.Name;
+import org.springframework.boot.jackson.NameAndAge;
+
+@JsonMixin(type = { Name.class, NameAndAge.class })
+public class EmptyMixInClass {
+
+}