Honor @Autowired(required=false) at parameter level

Issue: SPR-15268
(cherry picked from commit d74542e)

spring-beans/src/main/java/org/springframework/beans/factory/InjectionPoint.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -111,6 +111,17 @@ public class InjectionPoint {
 		}
 	}
 
+	/**
+	 * Retrieve a field/parameter annotation of the given type, if any.
+	 * @param annotationType the annotation type to retrieve
+	 * @return the annotation instance, or {@code null} if none found
+	 * @since 4.3.9
+	 */
+	public <A extends Annotation> A getAnnotation(Class<A> annotationType) {
+		return (this.field != null ? this.field.getAnnotation(annotationType) :
+				this.methodParameter.getParameterAnnotation(annotationType));
+	}
+
 	/**
 	 * Return the type declared by the underlying field or method/constructor parameter,
 	 * indicating the injection type.

spring-beans/src/main/java/org/springframework/beans/factory/annotation/QualifierAnnotationAutowireCandidateResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -309,7 +309,21 @@ public class QualifierAnnotationAutowireCandidateResolver extends GenericTypeAwa
 
 
 	/**
-	 * Determine whether the given dependency carries a value annotation.
+	 * Determine whether the given dependency declares an autowired annotation,
+	 * checking its required flag.
+	 * @see Autowired#required()
+	 */
+	@Override
+	public boolean isRequired(DependencyDescriptor descriptor) {
+		if (!super.isRequired(descriptor)) {
+			return false;
+		}
+		Autowired autowired = descriptor.getAnnotation(Autowired.class);
+		return (autowired == null || autowired.required());
+	}
+
+	/**
+	 * Determine whether the given dependency declares a value annotation.
 	 * @see Value
 	 */
 	@Override

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

@@ -1100,7 +1100,7 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 
 			Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
 			if (matchingBeans.isEmpty()) {
-				if (descriptor.isRequired()) {
+				if (isRequired(descriptor)) {
 					raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
 				}
 				return null;
@@ -1112,7 +1112,7 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 			if (matchingBeans.size() > 1) {
 				autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor);
 				if (autowiredBeanName == null) {
-					if (descriptor.isRequired() || !indicatesMultipleBeans(type)) {
+					if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {
 						return descriptor.resolveNotUnique(type, matchingBeans);
 					}
 					else {
@@ -1217,6 +1217,13 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 		}
 	}
 
+	private boolean isRequired(DependencyDescriptor descriptor) {
+		AutowireCandidateResolver resolver = getAutowireCandidateResolver();
+		return (resolver instanceof SimpleAutowireCandidateResolver ?
+				((SimpleAutowireCandidateResolver) resolver).isRequired(descriptor) :
+				descriptor.isRequired());
+	}
+
 	private boolean indicatesMultipleBeans(Class<?> type) {
 		return (type.isArray() || (type.isInterface() &&
 				(Collection.class.isAssignableFrom(type) || Map.class.isAssignableFrom(type))));

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -40,7 +40,8 @@ import org.springframework.util.ClassUtils;
  * @author Juergen Hoeller
  * @since 4.0
  */
-public class GenericTypeAwareAutowireCandidateResolver implements AutowireCandidateResolver, BeanFactoryAware {
+public class GenericTypeAwareAutowireCandidateResolver extends SimpleAutowireCandidateResolver
+		implements BeanFactoryAware {
 
 	private BeanFactory beanFactory;
 
@@ -57,8 +58,8 @@ public class GenericTypeAwareAutowireCandidateResolver implements AutowireCandid
 
 	@Override
 	public boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
-		if (!bdHolder.getBeanDefinition().isAutowireCandidate()) {
-			// if explicitly false, do not proceed with any other checks
+		if (!super.isAutowireCandidate(bdHolder, descriptor)) {
+			// If explicitly false, do not proceed with any other checks...
 			return false;
 		}
 		return (descriptor == null || checkGenericTypeMatch(bdHolder, descriptor));
@@ -166,23 +167,4 @@ public class GenericTypeAwareAutowireCandidateResolver implements AutowireCandid
 		return null;
 	}
 
-
-	/**
-	 * This implementation always returns {@code null}, leaving suggested value support up
-	 * to subclasses.
-	 */
-	@Override
-	public Object getSuggestedValue(DependencyDescriptor descriptor) {
-		return null;
-	}
-
-	/**
-	 * This implementation always returns {@code null}, leaving lazy resolution support up
-	 * to subclasses.
-	 */
-	@Override
-	public Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor, String beanName) {
-		return null;
-	}
-
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -16,7 +16,6 @@
 
 package org.springframework.beans.factory.support;
 
-import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinitionHolder;
 import org.springframework.beans.factory.config.DependencyDescriptor;
 
@@ -27,20 +26,27 @@ import org.springframework.beans.factory.config.DependencyDescriptor;
  * @author Mark Fisher
  * @author Juergen Hoeller
  * @since 2.5
- * @see BeanDefinition#isAutowireCandidate()
  */
 public class SimpleAutowireCandidateResolver implements AutowireCandidateResolver {
 
-	/**
-	 * Determine if the provided bean definition is an autowire candidate.
-	 * <p>To be considered a candidate the bean's <em>autowire-candidate</em>
-	 * attribute must not have been set to 'false'.
-	 */
 	@Override
 	public boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
 		return bdHolder.getBeanDefinition().isAutowireCandidate();
 	}
 
+	/**
+	 * Determine whether the given descriptor is effectively required.
+	 * <p>The default implementation checks {@link DependencyDescriptor#isRequired()}.
+	 * @param descriptor the descriptor for the target method parameter or field
+	 * @return whether the descriptor is marked as required or possibly indicating
+	 * non-required status some other way (e.g. through a parameter annotation)
+	 * @since 4.3.9
+	 * @see DependencyDescriptor#isRequired()
+	 */
+	public boolean isRequired(DependencyDescriptor descriptor) {
+		return descriptor.isRequired();
+	}
+
 	@Override
 	public Object getSuggestedValue(DependencyDescriptor descriptor) {
 		return null;