Merge branch '5.2.x'

# Conflicts:
#	spring-messaging/src/main/java/org/springframework/messaging/converter/MappingJackson2MessageConverter.java

spring-beans/src/main/java/org/springframework/beans/factory/support/CglibSubclassingInstantiationStrategy.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -238,8 +238,10 @@ public class CglibSubclassingInstantiationStrategy extends SimpleInstantiationSt
 			Assert.state(lo != null, "LookupOverride not found");
 			Object[] argsToUse = (args.length > 0 ? args : null);  // if no-arg, don't insist on args at all
 			if (StringUtils.hasText(lo.getBeanName())) {
-				return (argsToUse != null ? this.owner.getBean(lo.getBeanName(), argsToUse) :
+				Object bean = (argsToUse != null ? this.owner.getBean(lo.getBeanName(), argsToUse) :
 						this.owner.getBean(lo.getBeanName()));
+				// Detect package-protected NullBean instance through equals(null) check
+				return (bean.equals(null) ? null : bean);
 			}
 			else {
 				return (argsToUse != null ? this.owner.getBean(method.getReturnType(), argsToUse) :

spring-beans/src/test/java/org/springframework/beans/factory/annotation/LookupAnnotationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -108,10 +108,23 @@ public class LookupAnnotationTests {
 		assertThat(beanFactory.getBean(BeanConsumer.class).abstractBean).isSameAs(bean);
 	}
 
+	@Test  // gh-25806
+	public void testWithNullBean() {
+		RootBeanDefinition tbd = new RootBeanDefinition(TestBean.class, () -> null);
+		tbd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
+		beanFactory.registerBeanDefinition("testBean", tbd);
+
+		AbstractBean bean = beanFactory.getBean("beanConsumer", BeanConsumer.class).abstractBean;
+		assertThat(bean).isNotNull();
+		Object expected = bean.get();
+		assertThat(expected).isNull();
+		assertThat(beanFactory.getBean(BeanConsumer.class).abstractBean).isSameAs(bean);
+	}
+
 
 	public static abstract class AbstractBean {
 
-		@Lookup
+		@Lookup("testBean")
 		public abstract TestBean get();
 
 		@Lookup

spring-context/src/main/java/org/springframework/context/event/AbstractApplicationEventMulticaster.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -63,9 +63,9 @@ import org.springframework.util.ObjectUtils;
 public abstract class AbstractApplicationEventMulticaster
 		implements ApplicationEventMulticaster, BeanClassLoaderAware, BeanFactoryAware {
 
-	private final ListenerRetriever defaultRetriever = new ListenerRetriever(false);
+	private final DefaultListenerRetriever defaultRetriever = new DefaultListenerRetriever();
 
-	final Map<ListenerCacheKey, ListenerRetriever> retrieverCache = new ConcurrentHashMap<>(64);
+	final Map<ListenerCacheKey, CachedListenerRetriever> retrieverCache = new ConcurrentHashMap<>(64);
 
 	@Nullable
 	private ClassLoader beanClassLoader;
@@ -73,8 +73,6 @@ public abstract class AbstractApplicationEventMulticaster
 	@Nullable
 	private ConfigurableBeanFactory beanFactory;
 
-	private Object retrievalMutex = this.defaultRetriever;
-
 
 	@Override
 	public void setBeanClassLoader(ClassLoader classLoader) {
@@ -90,7 +88,6 @@ public abstract class AbstractApplicationEventMulticaster
 		if (this.beanClassLoader == null) {
 			this.beanClassLoader = this.beanFactory.getBeanClassLoader();
 		}
-		this.retrievalMutex = this.beanFactory.getSingletonMutex();
 	}
 
 	private ConfigurableBeanFactory getBeanFactory() {
@@ -104,7 +101,7 @@ public abstract class AbstractApplicationEventMulticaster
 
 	@Override
 	public void addApplicationListener(ApplicationListener<?> listener) {
-		synchronized (this.retrievalMutex) {
+		synchronized (this.defaultRetriever) {
 			// Explicitly remove target for a proxy, if registered already,
 			// in order to avoid double invocations of the same listener.
 			Object singletonTarget = AopProxyUtils.getSingletonTarget(listener);
@@ -118,7 +115,7 @@ public abstract class AbstractApplicationEventMulticaster
 
 	@Override
 	public void addApplicationListenerBean(String listenerBeanName) {
-		synchronized (this.retrievalMutex) {
+		synchronized (this.defaultRetriever) {
 			this.defaultRetriever.applicationListenerBeans.add(listenerBeanName);
 			this.retrieverCache.clear();
 		}
@@ -126,7 +123,7 @@ public abstract class AbstractApplicationEventMulticaster
 
 	@Override
 	public void removeApplicationListener(ApplicationListener<?> listener) {
-		synchronized (this.retrievalMutex) {
+		synchronized (this.defaultRetriever) {
 			this.defaultRetriever.applicationListeners.remove(listener);
 			this.retrieverCache.clear();
 		}
@@ -134,7 +131,7 @@ public abstract class AbstractApplicationEventMulticaster
 
 	@Override
 	public void removeApplicationListenerBean(String listenerBeanName) {
-		synchronized (this.retrievalMutex) {
+		synchronized (this.defaultRetriever) {
 			this.defaultRetriever.applicationListenerBeans.remove(listenerBeanName);
 			this.retrieverCache.clear();
 		}
@@ -142,7 +139,7 @@ public abstract class AbstractApplicationEventMulticaster
 
 	@Override
 	public void removeAllListeners() {
-		synchronized (this.retrievalMutex) {
+		synchronized (this.defaultRetriever) {
 			this.defaultRetriever.applicationListeners.clear();
 			this.defaultRetriever.applicationListenerBeans.clear();
 			this.retrieverCache.clear();
@@ -156,7 +153,7 @@ public abstract class AbstractApplicationEventMulticaster
 	 * @see org.springframework.context.ApplicationListener
 	 */
 	protected Collection<ApplicationListener<?>> getApplicationListeners() {
-		synchronized (this.retrievalMutex) {
+		synchronized (this.defaultRetriever) {
 			return this.defaultRetriever.getApplicationListeners();
 		}
 	}
@@ -177,32 +174,34 @@ public abstract class AbstractApplicationEventMulticaster
 		Class<?> sourceType = (source != null ? source.getClass() : null);
 		ListenerCacheKey cacheKey = new ListenerCacheKey(eventType, sourceType);
 
-		// Quick check for existing entry on ConcurrentHashMap...
+		// Potential new retriever to populate
-		ListenerRetriever retriever = this.retrieverCache.get(cacheKey);
+		CachedListenerRetriever newRetriever = null;
-		if (retriever != null) {
-			return retriever.getApplicationListeners();
-		}
 
-		if (this.beanClassLoader == null ||
+		// Quick check for existing entry on ConcurrentHashMap
-				(ClassUtils.isCacheSafe(event.getClass(), this.beanClassLoader) &&
+		CachedListenerRetriever existingRetriever = this.retrieverCache.get(cacheKey);
-						(sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {
+		if (existingRetriever == null) {
-			// Fully synchronized building and caching of a ListenerRetriever
+			// Caching a new ListenerRetriever if possible
-			synchronized (this.retrievalMutex) {
+			if (this.beanClassLoader == null ||
-				retriever = this.retrieverCache.get(cacheKey);
+					(ClassUtils.isCacheSafe(event.getClass(), this.beanClassLoader) &&
-				if (retriever != null) {
+							(sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {
-					return retriever.getApplicationListeners();
+				newRetriever = new CachedListenerRetriever();
+				existingRetriever = this.retrieverCache.putIfAbsent(cacheKey, newRetriever);
+				if (existingRetriever != null) {
+					newRetriever = null;  // no need to populate it in retrieveApplicationListeners
 				}
-				retriever = new ListenerRetriever(true);
-				Collection<ApplicationListener<?>> listeners =
-						retrieveApplicationListeners(eventType, sourceType, retriever);
-				this.retrieverCache.put(cacheKey, retriever);
-				return listeners;
 			}
 		}
-		else {
+
-			// No ListenerRetriever caching -> no synchronization necessary
+		if (existingRetriever != null) {
-			return retrieveApplicationListeners(eventType, sourceType, null);
+			Collection<ApplicationListener<?>> result = existingRetriever.getApplicationListeners();
+			if (result != null) {
+				return result;
+			}
+			// If result is null, the existing retriever is not fully populated yet by another thread.
+			// Proceed like caching wasn't possible for this current local attempt.
 		}
+
+		return retrieveApplicationListeners(eventType, sourceType, newRetriever);
 	}
 
 	/**
@@ -213,12 +212,15 @@ public abstract class AbstractApplicationEventMulticaster
 	 * @return the pre-filtered list of application listeners for the given event and source type
 	 */
 	private Collection<ApplicationListener<?>> retrieveApplicationListeners(
-			ResolvableType eventType, @Nullable Class<?> sourceType, @Nullable ListenerRetriever retriever) {
+			ResolvableType eventType, @Nullable Class<?> sourceType, @Nullable CachedListenerRetriever retriever) {
 
 		List<ApplicationListener<?>> allListeners = new ArrayList<>();
+		Set<ApplicationListener<?>> filteredListeners = (retriever != null ? new LinkedHashSet<>() : null);
+		Set<String> filteredListenerBeans = (retriever != null ? new LinkedHashSet<>() : null);
+
 		Set<ApplicationListener<?>> listeners;
 		Set<String> listenerBeans;
-		synchronized (this.retrievalMutex) {
+		synchronized (this.defaultRetriever) {
 			listeners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);
 			listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);
 		}
@@ -228,7 +230,7 @@ public abstract class AbstractApplicationEventMulticaster
 		for (ApplicationListener<?> listener : listeners) {
 			if (supportsEvent(listener, eventType, sourceType)) {
 				if (retriever != null) {
-					retriever.applicationListeners.add(listener);
+					filteredListeners.add(listener);
 				}
 				allListeners.add(listener);
 			}
@@ -246,10 +248,10 @@ public abstract class AbstractApplicationEventMulticaster
 						if (!allListeners.contains(listener) && supportsEvent(listener, eventType, sourceType)) {
 							if (retriever != null) {
 								if (beanFactory.isSingleton(listenerBeanName)) {
-									retriever.applicationListeners.add(listener);
+									filteredListeners.add(listener);
 								}
 								else {
-									retriever.applicationListenerBeans.add(listenerBeanName);
+									filteredListenerBeans.add(listenerBeanName);
 								}
 							}
 							allListeners.add(listener);
@@ -261,7 +263,7 @@ public abstract class AbstractApplicationEventMulticaster
 						// BeanDefinition metadata (e.g. factory method generics) above.
 						Object listener = beanFactory.getSingleton(listenerBeanName);
 						if (retriever != null) {
-							retriever.applicationListeners.remove(listener);
+							filteredListeners.remove(listener);
 						}
 						allListeners.remove(listener);
 					}
@@ -274,9 +276,15 @@ public abstract class AbstractApplicationEventMulticaster
 		}
 
 		AnnotationAwareOrderComparator.sort(allListeners);
-		if (retriever != null && retriever.applicationListenerBeans.isEmpty()) {
+		if (retriever != null) {
-			retriever.applicationListeners.clear();
+			if (filteredListenerBeans.isEmpty()) {
-			retriever.applicationListeners.addAll(allListeners);
+				retriever.applicationListeners = new LinkedHashSet<>(allListeners);
+				retriever.applicationListenerBeans = filteredListenerBeans;
+			}
+			else {
+				retriever.applicationListeners = filteredListeners;
+				retriever.applicationListenerBeans = filteredListenerBeans;
+			}
 		}
 		return allListeners;
 	}
@@ -415,18 +423,55 @@ public abstract class AbstractApplicationEventMulticaster
 	 * allowing for efficient retrieval of pre-filtered listeners.
 	 * <p>An instance of this helper gets cached per event type and source type.
 	 */
-	private class ListenerRetriever {
+	private class CachedListenerRetriever {
+
+		@Nullable
+		public volatile Set<ApplicationListener<?>> applicationListeners;
+
+		@Nullable
+		public volatile Set<String> applicationListenerBeans;
+
+		@Nullable
+		public Collection<ApplicationListener<?>> getApplicationListeners() {
+			Set<ApplicationListener<?>> applicationListeners = this.applicationListeners;
+			Set<String> applicationListenerBeans = this.applicationListenerBeans;
+			if (applicationListeners == null || applicationListenerBeans == null) {
+				// Not fully populated yet
+				return null;
+			}
+
+			List<ApplicationListener<?>> allListeners = new ArrayList<>(
+					applicationListeners.size() + applicationListenerBeans.size());
+			allListeners.addAll(applicationListeners);
+			if (!applicationListenerBeans.isEmpty()) {
+				BeanFactory beanFactory = getBeanFactory();
+				for (String listenerBeanName : applicationListenerBeans) {
+					try {
+						allListeners.add(beanFactory.getBean(listenerBeanName, ApplicationListener.class));
+					}
+					catch (NoSuchBeanDefinitionException ex) {
+						// Singleton listener instance (without backing bean definition) disappeared -
+						// probably in the middle of the destruction phase
+					}
+				}
+			}
+			if (!applicationListenerBeans.isEmpty()) {
+				AnnotationAwareOrderComparator.sort(allListeners);
+			}
+			return allListeners;
+		}
+	}
+
+
+	/**
+	 * Helper class that encapsulates a general set of target listeners.
+	 */
+	private class DefaultListenerRetriever {
 
 		public final Set<ApplicationListener<?>> applicationListeners = new LinkedHashSet<>();
 
 		public final Set<String> applicationListenerBeans = new LinkedHashSet<>();
 
-		private final boolean preFiltered;
-
-		public ListenerRetriever(boolean preFiltered) {
-			this.preFiltered = preFiltered;
-		}
-
 		public Collection<ApplicationListener<?>> getApplicationListeners() {
 			List<ApplicationListener<?>> allListeners = new ArrayList<>(
 					this.applicationListeners.size() + this.applicationListenerBeans.size());
@@ -435,8 +480,9 @@ public abstract class AbstractApplicationEventMulticaster
 				BeanFactory beanFactory = getBeanFactory();
 				for (String listenerBeanName : this.applicationListenerBeans) {
 					try {
-						ApplicationListener<?> listener = beanFactory.getBean(listenerBeanName, ApplicationListener.class);
+						ApplicationListener<?> listener =
-						if (this.preFiltered || !allListeners.contains(listener)) {
+								beanFactory.getBean(listenerBeanName, ApplicationListener.class);
+						if (!allListeners.contains(listener)) {
 							allListeners.add(listener);
 						}
 					}
@@ -446,9 +492,7 @@ public abstract class AbstractApplicationEventMulticaster
 					}
 				}
 			}
-			if (!this.preFiltered || !this.applicationListenerBeans.isEmpty()) {
+			AnnotationAwareOrderComparator.sort(allListeners);
-				AnnotationAwareOrderComparator.sort(allListeners);
-			}
 			return allListeners;
 		}
 	}

spring-context/src/test/java/org/springframework/context/event/ApplicationContextEventTests.java

@@ -27,6 +27,7 @@ import org.junit.jupiter.api.Test;
 
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.InitializingBean;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.beans.factory.config.RuntimeBeanReference;
@@ -35,6 +36,8 @@ import org.springframework.beans.testfixture.beans.TestBean;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
 import org.springframework.context.ApplicationEvent;
+import org.springframework.context.ApplicationEventPublisher;
+import org.springframework.context.ApplicationEventPublisherAware;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.PayloadApplicationEvent;
 import org.springframework.context.support.AbstractApplicationContext;
@@ -374,6 +377,19 @@ public class ApplicationContextEventTests extends AbstractApplicationEventListen
 		assertThat(MyNonSingletonListener.seenEvents.contains(event4)).isTrue();
 		MyNonSingletonListener.seenEvents.clear();
 
+		context.publishEvent(event1);
+		context.publishEvent(event2);
+		context.publishEvent(event3);
+		context.publishEvent(event4);
+		assertThat(MyNonSingletonListener.seenEvents.contains(event1)).isTrue();
+		assertThat(MyNonSingletonListener.seenEvents.contains(event2)).isTrue();
+		assertThat(MyNonSingletonListener.seenEvents.contains(event3)).isTrue();
+		assertThat(MyNonSingletonListener.seenEvents.contains(event4)).isTrue();
+		MyNonSingletonListener.seenEvents.clear();
+
+		AbstractApplicationEventMulticaster multicaster = context.getBean(AbstractApplicationEventMulticaster.class);
+		assertThat(multicaster.retrieverCache.size()).isEqualTo(3);
+
 		context.close();
 	}
 
@@ -516,6 +532,36 @@ public class ApplicationContextEventTests extends AbstractApplicationEventListen
 		context.close();
 	}
 
+	@Test
+	public void initMethodPublishesEvent() {
+		GenericApplicationContext context = new GenericApplicationContext();
+		context.registerBeanDefinition("listener", new RootBeanDefinition(BeanThatListens.class));
+		context.registerBeanDefinition("messageSource", new RootBeanDefinition(StaticMessageSource.class));
+		context.registerBeanDefinition("initMethod", new RootBeanDefinition(EventPublishingInitMethod.class));
+		context.refresh();
+
+		context.publishEvent(new MyEvent(this));
+		BeanThatListens listener = context.getBean(BeanThatListens.class);
+		assertThat(listener.getEventCount()).isEqualTo(3);
+
+		context.close();
+	}
+
+	@Test
+	public void initMethodPublishesAsyncEvent() {
+		GenericApplicationContext context = new GenericApplicationContext();
+		context.registerBeanDefinition("listener", new RootBeanDefinition(BeanThatListens.class));
+		context.registerBeanDefinition("messageSource", new RootBeanDefinition(StaticMessageSource.class));
+		context.registerBeanDefinition("initMethod", new RootBeanDefinition(AsyncEventPublishingInitMethod.class));
+		context.refresh();
+
+		context.publishEvent(new MyEvent(this));
+		BeanThatListens listener = context.getBean(BeanThatListens.class);
+		assertThat(listener.getEventCount()).isEqualTo(3);
+
+		context.close();
+	}
+
 
 	@SuppressWarnings("serial")
 	public static class MyEvent extends ApplicationEvent {
@@ -652,4 +698,38 @@ public class ApplicationContextEventTests extends AbstractApplicationEventListen
 		}
 	}
 
+
+	public static class EventPublishingInitMethod implements ApplicationEventPublisherAware, InitializingBean {
+
+		private ApplicationEventPublisher publisher;
+
+		@Override
+		public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
+			this.publisher = applicationEventPublisher;
+		}
+
+		@Override
+		public void afterPropertiesSet() throws Exception {
+			this.publisher.publishEvent(new MyEvent(this));
+		}
+	}
+
+
+	public static class AsyncEventPublishingInitMethod implements ApplicationEventPublisherAware, InitializingBean {
+
+		private ApplicationEventPublisher publisher;
+
+		@Override
+		public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
+			this.publisher = applicationEventPublisher;
+		}
+
+		@Override
+		public void afterPropertiesSet() throws Exception {
+			Thread thread = new Thread(() -> this.publisher.publishEvent(new MyEvent(this)));
+			thread.start();
+			thread.join();
+		}
+	}
+
 }

spring-core/src/main/java/org/springframework/util/ObjectUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -132,14 +132,13 @@ public abstract class ObjectUtils {
 	 * @see CollectionUtils#isEmpty(java.util.Collection)
 	 * @see CollectionUtils#isEmpty(java.util.Map)
 	 */
-	@SuppressWarnings("rawtypes")
 	public static boolean isEmpty(@Nullable Object obj) {
 		if (obj == null) {
 			return true;
 		}
 
 		if (obj instanceof Optional) {
-			return !((Optional) obj).isPresent();
+			return !((Optional<?>) obj).isPresent();
 		}
 		if (obj instanceof CharSequence) {
 			return ((CharSequence) obj).length() == 0;
@@ -148,10 +147,10 @@ public abstract class ObjectUtils {
 			return Array.getLength(obj) == 0;
 		}
 		if (obj instanceof Collection) {
-			return ((Collection) obj).isEmpty();
+			return ((Collection<?>) obj).isEmpty();
 		}
 		if (obj instanceof Map) {
-			return ((Map) obj).isEmpty();
+			return ((Map<?, ?>) obj).isEmpty();
 		}
 
 		// else
@@ -611,9 +610,7 @@ public abstract class ObjectUtils {
 		if (obj == null) {
 			return EMPTY_STRING;
 		}
-		String className = obj.getClass().getName();
+		return obj.getClass().getName() + "@" + getIdentityHexString(obj);
-		String identityHexString = getIdentityHexString(obj);
-		return className + '@' + identityHexString;
 	}
 
 	/**

spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/CallMetaDataProviderFactory.java

@@ -43,6 +43,7 @@ public final class CallMetaDataProviderFactory {
 			"Apache Derby",
 			"DB2",
 			"Informix Dynamic Server",
+			"MariaDB",
 			"Microsoft SQL Server",
 			"MySQL",
 			"Oracle",

spring-jms/src/main/java/org/springframework/jms/support/converter/MappingJackson2MessageConverter.java

@@ -457,11 +457,11 @@ public class MappingJackson2MessageConverter implements SmartMessageConverter, B
 		}
 		Class<?> mappedClass = this.idClassMappings.get(typeId);
 		if (mappedClass != null) {
-			return this.objectMapper.getTypeFactory().constructType(mappedClass);
+			return this.objectMapper.constructType(mappedClass);
 		}
 		try {
 			Class<?> typeClass = ClassUtils.forName(typeId, this.beanClassLoader);
-			return this.objectMapper.getTypeFactory().constructType(typeClass);
+			return this.objectMapper.constructType(typeClass);
 		}
 		catch (Throwable ex) {
 			throw new MessageConversionException("Failed to resolve type id [" + typeId + "]", ex);

spring-messaging/src/main/java/org/springframework/messaging/converter/MarshallingMessageConverter.java

@@ -46,6 +46,8 @@ import org.springframework.util.MimeType;
  *
  * @author Arjen Poutsma
  * @since 4.2
+ * @see Marshaller
+ * @see Unmarshaller
  */
 public class MarshallingMessageConverter extends AbstractMessageConverter {
 
@@ -61,7 +63,8 @@ public class MarshallingMessageConverter extends AbstractMessageConverter {
 	 * {@link #setUnmarshaller(Unmarshaller)} to be invoked separately.
 	 */
 	public MarshallingMessageConverter() {
-		this(new MimeType("application", "xml"), new MimeType("text", "xml"), new MimeType("application", "*+xml"));
+		this(new MimeType("application", "xml"), new MimeType("text", "xml"),
+				new MimeType("application", "*+xml"));
 	}
 
 	/**
@@ -160,7 +163,7 @@ public class MarshallingMessageConverter extends AbstractMessageConverter {
 			return new StreamSource(new ByteArrayInputStream((byte[]) payload));
 		}
 		else {
-			return new StreamSource(new StringReader((String) payload));
+			return new StreamSource(new StringReader(payload.toString()));
 		}
 	}
 

spring-messaging/src/main/java/org/springframework/messaging/converter/ProtobufMessageConverter.java

@@ -120,9 +120,9 @@ public class ProtobufMessageConverter extends AbstractMessageConverter {
 
 	@Override
 	protected boolean canConvertTo(Object payload, @Nullable MessageHeaders headers) {
-		MimeType mimeType = getMimeType(headers);
+		MimeType contentType = getMimeType(headers);
 		return (super.canConvertTo(payload, headers) ||
-				this.protobufFormatSupport != null && this.protobufFormatSupport.supportsWriteOnly(mimeType));
+				this.protobufFormatSupport != null && this.protobufFormatSupport.supportsWriteOnly(contentType));
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/http/codec/json/AbstractJackson2Decoder.java

@@ -97,7 +97,7 @@ public abstract class AbstractJackson2Decoder extends Jackson2CodecSupport imple
 
 	@Override
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		JavaType javaType = getObjectMapper().getTypeFactory().constructType(elementType.getType());
+		JavaType javaType = getObjectMapper().constructType(elementType.getType());
 		// Skip String: CharSequenceDecoder + "*/*" comes after
 		return (!CharSequence.class.isAssignableFrom(elementType.toClass()) &&
 				getObjectMapper().canDeserialize(javaType) && supportsMimeType(mimeType));

spring-web/src/main/java/org/springframework/http/codec/json/Jackson2CodecSupport.java

@@ -27,7 +27,6 @@ import java.util.Map;
 import com.fasterxml.jackson.annotation.JsonView;
 import com.fasterxml.jackson.databind.JavaType;
 import com.fasterxml.jackson.databind.ObjectMapper;
-import com.fasterxml.jackson.databind.type.TypeFactory;
 import org.apache.commons.logging.Log;
 
 import org.springframework.core.GenericTypeResolver;
@@ -113,8 +112,7 @@ public abstract class Jackson2CodecSupport {
 	}
 
 	protected JavaType getJavaType(Type type, @Nullable Class<?> contextClass) {
-		TypeFactory typeFactory = this.objectMapper.getTypeFactory();
+		return this.objectMapper.constructType(GenericTypeResolver.resolveType(type, contextClass));
-		return typeFactory.constructType(GenericTypeResolver.resolveType(type, contextClass));
 	}
 
 	protected Map<String, Object> getHints(ResolvableType resolvableType) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -25,7 +25,7 @@ import org.springframework.http.MediaType;
 import org.springframework.lang.Nullable;
 
 /**
- * Strategy interface that specifies a converter that can convert from and to HTTP requests and responses.
+ * Strategy interface for converting from and to HTTP requests and responses.
  *
  * @author Arjen Poutsma
  * @author Juergen Hoeller

spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java

@@ -42,7 +42,6 @@ import com.fasterxml.jackson.databind.SerializationConfig;
 import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.databind.exc.InvalidDefinitionException;
 import com.fasterxml.jackson.databind.ser.FilterProvider;
-import com.fasterxml.jackson.databind.type.TypeFactory;
 
 import org.springframework.core.GenericTypeResolver;
 import org.springframework.http.HttpInputMessage;
@@ -377,8 +376,7 @@ public abstract class AbstractJackson2HttpMessageConverter extends AbstractGener
 	 * @return the Jackson JavaType
 	 */
 	protected JavaType getJavaType(Type type, @Nullable Class<?> contextClass) {
-		TypeFactory typeFactory = this.objectMapper.getTypeFactory();
+		return this.objectMapper.constructType(GenericTypeResolver.resolveType(type, contextClass));
-		return typeFactory.constructType(GenericTypeResolver.resolveType(type, contextClass));
 	}
 
 	/**

spring-web/src/main/java/org/springframework/web/client/RestTemplate.java

@@ -121,9 +121,8 @@ public class RestTemplate extends InterceptingHttpAccessor implements RestOperat
 		ClassLoader classLoader = RestTemplate.class.getClassLoader();
 		romePresent = ClassUtils.isPresent("com.rometools.rome.feed.WireFeed", classLoader);
 		jaxb2Present = ClassUtils.isPresent("javax.xml.bind.Binder", classLoader);
-		jackson2Present =
+		jackson2Present = ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", classLoader) &&
-				ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", classLoader) &&
+				ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", classLoader);
-						ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", classLoader);
 		jackson2XmlPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.xml.XmlMapper", classLoader);
 		jackson2SmilePresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.smile.SmileFactory", classLoader);
 		jackson2CborPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.cbor.CBORFactory", classLoader);

spring-web/src/main/java/org/springframework/web/util/UriComponentsBuilder.java

@@ -34,6 +34,7 @@ import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpRequest;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.util.ObjectUtils;
@@ -454,9 +455,8 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 	 * characters that should have been encoded.
 	 */
 	public UriComponents build(boolean encoded) {
-		return buildInternal(encoded ?
+		return buildInternal(encoded ? EncodingHint.FULLY_ENCODED :
-				EncodingHint.FULLY_ENCODED :
+				(this.encodeTemplate ? EncodingHint.ENCODE_TEMPLATE : EncodingHint.NONE));
-				this.encodeTemplate ? EncodingHint.ENCODE_TEMPLATE : EncodingHint.NONE);
 	}
 
 	private UriComponents buildInternal(EncodingHint hint) {
@@ -468,8 +468,7 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 			HierarchicalUriComponents uric = new HierarchicalUriComponents(this.scheme, this.fragment,
 					this.userInfo, this.host, this.port, this.pathBuilder.build(), this.queryParams,
 					hint == EncodingHint.FULLY_ENCODED);
-
+			result = (hint == EncodingHint.ENCODE_TEMPLATE ? uric.encodeTemplate(this.charset) : uric);
-			result = hint == EncodingHint.ENCODE_TEMPLATE ? uric.encodeTemplate(this.charset) : uric;
 		}
 		if (!this.uriVariables.isEmpty()) {
 			result = result.expand(name -> this.uriVariables.getOrDefault(name, UriTemplateVariables.SKIP_VALUE));
@@ -526,9 +525,8 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 	 * @see UriComponents#toUriString()
 	 */
 	public String toUriString() {
-		return this.uriVariables.isEmpty() ?
+		return (this.uriVariables.isEmpty() ? build().encode().toUriString() :
-				build().encode().toUriString() :
+				buildInternal(EncodingHint.ENCODE_TEMPLATE).toUriString());
-				buildInternal(EncodingHint.ENCODE_TEMPLATE).toUriString();
 	}
 
 
@@ -712,7 +710,7 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 
 	@Override
 	public UriComponentsBuilder queryParam(String name, @Nullable Collection<?> values) {
-		return queryParam(name, values != null ? values.toArray() : EMPTY_VALUES);
+		return queryParam(name, (CollectionUtils.isEmpty(values) ? EMPTY_VALUES : values.toArray()));
 	}
 
 	/**
@@ -741,7 +739,7 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 
 	@Override
 	public UriComponentsBuilder replaceQueryParam(String name, @Nullable Collection<?> values) {
-		return replaceQueryParam(name, values != null ? values.toArray() : EMPTY_VALUES);
+		return replaceQueryParam(name, (CollectionUtils.isEmpty(values) ? EMPTY_VALUES : values.toArray()));
 	}
 
 	/**
@@ -830,12 +828,10 @@ public class UriComponentsBuilder implements UriBuilder, Cloneable {
 					scheme("https");
 					port(null);
 				}
-
 				String hostHeader = headers.getFirst("X-Forwarded-Host");
 				if (StringUtils.hasText(hostHeader)) {
 					adaptForwardedHost(StringUtils.tokenizeToStringArray(hostHeader, ",")[0]);
 				}
-
 				String portHeader = headers.getFirst("X-Forwarded-Port");
 				if (StringUtils.hasText(portHeader)) {
 					port(Integer.parseInt(StringUtils.tokenizeToStringArray(portHeader, ",")[0]));

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/MessageTag.java

@@ -358,20 +358,7 @@ public class MessageTag extends HtmlEscapingAwareTag implements ArgumentAware {
 	@Nullable
 	protected Object[] resolveArguments(@Nullable Object arguments) throws JspException {
 		if (arguments instanceof String) {
-			String[] stringArray =
+			return StringUtils.delimitedListToStringArray((String) arguments, this.argumentSeparator);
-					StringUtils.delimitedListToStringArray((String) arguments, this.argumentSeparator);
-			if (stringArray.length == 1) {
-				Object argument = stringArray[0];
-				if (argument != null && argument.getClass().isArray()) {
-					return ObjectUtils.toObjectArray(argument);
-				}
-				else {
-					return new Object[] {argument};
-				}
-			}
-			else {
-				return stringArray;
-			}
 		}
 		else if (arguments instanceof Object[]) {
 			return (Object[]) arguments;
@@ -395,7 +382,7 @@ public class MessageTag extends HtmlEscapingAwareTag implements ArgumentAware {
 	 * @throws IOException if writing failed
 	 */
 	protected void writeMessage(String msg) throws IOException {
-		this.pageContext.getOut().write(String.valueOf(msg));
+		this.pageContext.getOut().write(msg);
 	}
 
 	/**

spring-webmvc/src/main/java/org/springframework/web/servlet/view/RedirectView.java

@@ -20,7 +20,6 @@ import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 import java.lang.reflect.Array;
 import java.net.URLEncoder;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashMap;
@@ -35,6 +34,7 @@ import org.springframework.beans.BeanUtils;
 import org.springframework.http.HttpStatus;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.context.WebApplicationContext;
@@ -456,12 +456,12 @@ public class RedirectView extends AbstractUrlBasedView implements SmartView {
 		boolean first = (targetUrl.toString().indexOf('?') < 0);
 		for (Map.Entry<String, Object> entry : queryProperties(model).entrySet()) {
 			Object rawValue = entry.getValue();
-			Collection<Object> values;
+			Collection<?> values;
 			if (rawValue != null && rawValue.getClass().isArray()) {
-				values = Arrays.asList(ObjectUtils.toObjectArray(rawValue));
+				values = CollectionUtils.arrayToList(rawValue);
 			}
 			else if (rawValue instanceof Collection) {
-				values = ((Collection<Object>) rawValue);
+				values = ((Collection<?>) rawValue);
 			}
 			else {
 				values = Collections.singleton(rawValue);