Add @FunctionalInterface on candidate interfaces

Issue: SPR-14432

spring-beans/src/main/java/org/springframework/beans/factory/config/BeanFactoryPostProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -42,6 +42,7 @@ import org.springframework.beans.BeansException;
  * @see BeanPostProcessor
  * @see PropertyResourceConfigurer
  */
+@FunctionalInterface
 public interface BeanFactoryPostProcessor {
 
 	/**

spring-beans/src/main/java/org/springframework/beans/factory/parsing/SourceExtractor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -33,6 +33,7 @@ import org.springframework.core.io.Resource;
  * @see org.springframework.beans.BeanMetadataElement#getSource()
  * @see org.springframework.beans.factory.config.BeanDefinition
  */
+@FunctionalInterface
 public interface SourceExtractor {
 
 	/**

spring-beans/src/main/java/org/springframework/beans/factory/xml/NamespaceHandlerResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -25,6 +25,7 @@ package org.springframework.beans.factory.xml;
  * @see NamespaceHandler
  * @see org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader
  */
+@FunctionalInterface
 public interface NamespaceHandlerResolver {
 
 	/**