Add defaultUseWrapper support to Jackson builder

Issue: SPR-13975

spring-web/src/main/java/org/springframework/http/converter/json/Jackson2ObjectMapperBuilder.java

@@ -47,6 +47,8 @@ import com.fasterxml.jackson.databind.cfg.HandlerInstantiator;
 import com.fasterxml.jackson.databind.jsontype.TypeResolverBuilder;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 import com.fasterxml.jackson.databind.ser.FilterProvider;
+import com.fasterxml.jackson.dataformat.xml.JacksonXmlModule;
+import com.fasterxml.jackson.dataformat.xml.XmlFactory;
 import com.fasterxml.jackson.dataformat.xml.XmlMapper;
 
 import org.springframework.beans.BeanUtils;
@@ -127,6 +129,8 @@ public class Jackson2ObjectMapperBuilder {
 
 	private ApplicationContext applicationContext;
 
+	private Boolean defaultUseWrapper;
+
 
 	/**
 	 * If set to {@code true}, an {@link XmlMapper} will be created using its
@@ -392,6 +396,16 @@ public class Jackson2ObjectMapperBuilder {
 		return this;
 	}
 
+	/**
+	 * Define if a wrapper will be used for indexed (List, array) properties or not by
+	 * default (only applies to {@link XmlMapper}).
+	 * @since 4.3
+	 */
+	public Jackson2ObjectMapperBuilder defaultUseWrapper(boolean defaultUseWrapper) {
+		this.defaultUseWrapper = defaultUseWrapper;
+		return this;
+	}
+
 	/**
 	 * Specify features to enable.
 	 * @see com.fasterxml.jackson.core.JsonParser.Feature
@@ -547,7 +561,8 @@ public class Jackson2ObjectMapperBuilder {
 	public <T extends ObjectMapper> T build() {
 		ObjectMapper mapper;
 		if (this.createXmlMapper) {
-			mapper = new XmlObjectMapperInitializer().create();
+			mapper = (this.defaultUseWrapper == null ? new XmlObjectMapperInitializer().create()
+					: new XmlObjectMapperInitializer().create(this.defaultUseWrapper));
 		}
 		else {
 			mapper = new ObjectMapper();
@@ -757,11 +772,21 @@ public class Jackson2ObjectMapperBuilder {
 	private static class XmlObjectMapperInitializer {
 
 		public ObjectMapper create() {
+			return new XmlMapper(xmlInputFactory());
+		}
+
+		public ObjectMapper create(boolean defaultUseWrapper) {
+			JacksonXmlModule module = new JacksonXmlModule();
+			module.setDefaultUseWrapper(defaultUseWrapper);
+			return new XmlMapper(new XmlFactory(xmlInputFactory()), module);
+		}
+
+		private static final XMLInputFactory xmlInputFactory() {
 			XMLInputFactory inputFactory = XMLInputFactory.newInstance();
 			inputFactory.setProperty(XMLInputFactory.SUPPORT_DTD, false);
 			inputFactory.setProperty(XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES, false);
 			inputFactory.setXMLResolver(NO_OP_XML_RESOLVER);
-			return new XmlMapper(inputFactory);
+			return inputFactory;
 		}
 
 		private static final XMLResolver NO_OP_XML_RESOLVER = new XMLResolver() {

spring-web/src/main/java/org/springframework/http/converter/json/Jackson2ObjectMapperFactoryBean.java

@@ -324,6 +324,15 @@ public class Jackson2ObjectMapperFactoryBean implements FactoryBean<ObjectMapper
 		this.builder.indentOutput(indentOutput);
 	}
 
+	/**
+	 * Define if a wrapper will be used for indexed (List, array) properties or not by
+	 * default (only applies to {@link XmlMapper}).
+	 * @since 4.3
+	 */
+	public void setDefaultUseWrapper(boolean defaultUseWrapper) {
+		this.builder.defaultUseWrapper(defaultUseWrapper);
+	}
+
 	/**
 	 * Specify features to enable.
 	 * @see com.fasterxml.jackson.core.JsonParser.Feature

spring-web/src/test/java/org/springframework/http/converter/json/Jackson2ObjectMapperBuilderTests.java

@@ -22,9 +22,11 @@ import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.Date;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Optional;
@@ -437,6 +439,16 @@ public class Jackson2ObjectMapperBuilderTests {
 		assertTrue(xmlObjectMapper.getClass().isAssignableFrom(XmlMapper.class));
 	}
 
+	@Test  // SPR-13975
+	public void defaultUseWrapper() throws JsonProcessingException {
+		ObjectMapper objectMapper = Jackson2ObjectMapperBuilder.xml().defaultUseWrapper(false).build();
+		assertNotNull(objectMapper);
+		assertEquals(XmlMapper.class, objectMapper.getClass());
+		ListContainer<String> container = new ListContainer<>(Arrays.asList("foo", "bar"));
+		String output = objectMapper.writeValueAsString(container);
+		assertThat(output, containsString("<list>foo</list><list>bar</list></ListContainer>"));
+	}
+
 
 	public static class CustomIntegerModule extends Module {
 
@@ -501,4 +513,24 @@ public class Jackson2ObjectMapperBuilderTests {
 		}
 	}
 
+	public static class ListContainer<T> {
+
+		private List<T> list;
+
+		public ListContainer() {
+		}
+
+		public ListContainer(List<T> list) {
+			this.list = list;
+		}
+
+		public List<T> getList() {
+			return list;
+		}
+
+		public void setList(List<T> list) {
+			this.list = list;
+		}
+	}
+
 }