Make it easier to customize auto-configured Jackson2ObjectMapperBuilder

Previously, it was difficult to customize the auto-configured
Jackson2ObjectMapperBuilder. Typically, use of a bean post processor
was required.

This commit introduces Jackson2ObjectMapperBuilderCustomizer. Beans
that implement this interfaces are called during creation of the
auto-configured Jackson2ObjectMapperBuilder, providing an opportunity
to customize its configuration.

Closes gh-5803

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/Jackson2ObjectMapperBuilderCustomizer.java

+/*
+ * Copyright 2012-2016 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
+ *
+ *      http://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.autoconfigure.jackson;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
+
+/**
+ * Callback interface that can be implemented by beans wishing to further customize the
+ * {@link ObjectMapper} via {@link Jackson2ObjectMapperBuilder} retaining its default
+ * auto-configuration.
+ *
+ * @author Grzegorz Poznachowski
+ * @since 1.4.0
+ */
+public interface Jackson2ObjectMapperBuilderCustomizer {
+
+    /**
+     * Customize the jacksonObjectMapperBuilder.
+     * @param jacksonObjectMapperBuilder the jacksonObjectMapperBuilder to customize
+     */
+    void customize(Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder);
+}

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

@@ -21,6 +21,7 @@ import java.text.DateFormat;
 import java.text.SimpleDateFormat;
 import java.util.Collection;
 import java.util.Locale;
+import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.TimeZone;
@@ -41,6 +42,7 @@ import org.joda.time.format.DateTimeFormat;
 import org.springframework.beans.BeanUtils;
 import org.springframework.beans.factory.BeanFactoryUtils;
 import org.springframework.beans.factory.ListableBeanFactory;
+import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnJava;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnJava.JavaVersion;
@@ -51,6 +53,7 @@ import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Primary;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -85,13 +88,30 @@ public class JacksonAutoConfiguration {
 	@ConditionalOnClass({ ObjectMapper.class, Jackson2ObjectMapperBuilder.class })
 	static class JacksonObjectMapperConfiguration {
 
+		private final List<Jackson2ObjectMapperBuilderCustomizer> builderCustomizers;
+
+		JacksonObjectMapperConfiguration(
+				ObjectProvider<List<Jackson2ObjectMapperBuilderCustomizer>> builderCustomizersProvider) {
+			this.builderCustomizers = builderCustomizersProvider.getIfAvailable();
+		}
+
 		@Bean
 		@Primary
 		@ConditionalOnMissingBean(ObjectMapper.class)
 		public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
+			customize(builder);
 			return builder.createXmlMapper(false).build();
 		}
 
+		private void customize(Jackson2ObjectMapperBuilder builder) {
+			if (this.builderCustomizers != null) {
+				AnnotationAwareOrderComparator.sort(this.builderCustomizers);
+				for (Jackson2ObjectMapperBuilderCustomizer customizer : this.builderCustomizers) {
+					customizer.customize(builder);
+				}
+			}
+		}
+
 	}
 
 	@Configuration

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

@@ -72,6 +72,7 @@ import static org.mockito.Mockito.mock;
  * @author Marcel Overdijk
  * @author Sebastien Deleuze
  * @author Johannes Edmeier
+ * @author Grzegorz Poznachowski
  */
 public class JacksonAutoConfigurationTests {
 
@@ -419,6 +420,15 @@ public class JacksonAutoConfigurationTests {
 				.isEqualTo("\"Koordinierte Universalzeit\"");
 	}
 
+	@Test
+	public void additionalJacksonBuilderCustomization() throws Exception {
+		this.context.register(JacksonAutoConfiguration.class,
+				ObjectMapperBuilderCustomConfig.class);
+		this.context.refresh();
+		ObjectMapper mapper = this.context.getBean(ObjectMapper.class);
+		assertThat(mapper.getDateFormat()).isInstanceOf(MyDateFormat.class);
+	}
+
 	@Test
 	public void parameterNamesModuleIsAutoConfigured() {
 		assertParameterNamesModuleCreatorBinding(Mode.DEFAULT,
@@ -510,6 +520,21 @@ public class JacksonAutoConfigurationTests {
 
 	}
 
+	@Configuration
+	protected static class ObjectMapperBuilderCustomConfig {
+
+		@Bean
+		public Jackson2ObjectMapperBuilderCustomizer customDateFormat() {
+			return new Jackson2ObjectMapperBuilderCustomizer() {
+				@Override
+				public void customize(Jackson2ObjectMapperBuilder jackson2ObjectMapperBuilder) {
+					jackson2ObjectMapperBuilder.dateFormat(new MyDateFormat());
+				}
+			};
+		}
+
+	}
+
 	protected static final class Foo {
 
 		private String name;