Add @FunctionalInterface on candidate interfaces

Issue: SPR-14432

spring-core/src/main/java/org/springframework/core/MethodIntrospector.java

@@ -146,6 +146,7 @@ public abstract class MethodIntrospector {
 	 * A callback interface for metadata lookup on a given method.
 	 * @param <T> the type of metadata returned
 	 */
+	@FunctionalInterface
 	public interface MetadataLookup<T> {
 
 		/**

spring-core/src/main/java/org/springframework/core/OrderComparator.java

@@ -203,6 +203,7 @@ public class OrderComparator implements Comparator<Object> {
 	 * Strategy interface to provide an order source for a given object.
 	 * @since 4.1
 	 */
+	@FunctionalInterface
 	public interface OrderSourceProvider {
 
 		/**

spring-core/src/main/java/org/springframework/core/convert/converter/Converter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 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.
@@ -28,6 +28,7 @@ package org.springframework.core.convert.converter;
  * @param <S> the source type
  * @param <T> the target type
  */
+@FunctionalInterface
 public interface Converter<S, T> {
 
 	/**

spring-core/src/main/java/org/springframework/core/io/ProtocolResolver.java

@@ -27,6 +27,7 @@ package org.springframework.core.io;
  * @since 4.3
  * @see DefaultResourceLoader#addProtocolResolver
  */
+@FunctionalInterface
 public interface ProtocolResolver {
 
 	/**

spring-core/src/main/java/org/springframework/core/serializer/Deserializer.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.
@@ -26,6 +26,7 @@ import java.io.InputStream;
  * @author Mark Fisher
  * @since 3.0.5
  */
+@FunctionalInterface
 public interface Deserializer<T> {
 
 	/**

spring-core/src/main/java/org/springframework/core/serializer/Serializer.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.
@@ -26,6 +26,7 @@ import java.io.OutputStream;
  * @author Mark Fisher
  * @since 3.0.5
  */
+@FunctionalInterface
 public interface Serializer<T> {
 
 	/**

spring-core/src/main/java/org/springframework/core/task/TaskDecorator.java

@@ -32,6 +32,7 @@ package org.springframework.core.task;
  * @see TaskExecutor#execute(Runnable)
  * @see SimpleAsyncTaskExecutor#setTaskDecorator
  */
+@FunctionalInterface
 public interface TaskDecorator {
 
 	/**

spring-core/src/main/java/org/springframework/core/task/TaskExecutor.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.
@@ -35,6 +35,7 @@ import java.util.concurrent.Executor;
  * @since 2.0
  * @see java.util.concurrent.Executor
  */
+@FunctionalInterface
 public interface TaskExecutor extends Executor {
 
 	/**

spring-core/src/main/java/org/springframework/core/type/filter/TypeFilter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2007 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.
@@ -30,6 +30,7 @@ import org.springframework.core.type.classreading.MetadataReaderFactory;
  * @author Mark Fisher
  * @since 2.5
  */
+@FunctionalInterface
 public interface TypeFilter {
 
 	/**

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

@@ -243,6 +243,7 @@ public class AutoPopulatingList<E> implements List<E>, Serializable {
 	 * Factory interface for creating elements for an index-based access
 	 * data structure such as a {@link java.util.List}.
 	 */
+	@FunctionalInterface
 	public interface ElementFactory<E> {
 
 		/**

spring-core/src/main/java/org/springframework/util/ErrorHandler.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.util;
  * @author Mark Fisher
  * @since 3.0
  */
+@FunctionalInterface
 public interface ErrorHandler {
 
 	/**

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

@@ -212,7 +212,8 @@ public class PropertyPlaceholderHelper {
 	/**
 	 * Strategy interface used to resolve replacement values for placeholders contained in Strings.
 	 */
-	public static interface PlaceholderResolver {
+	@FunctionalInterface
+	public interface PlaceholderResolver {
 
 		/**
 		 * Resolve the supplied placeholder name to the replacement value.

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

@@ -755,6 +755,7 @@ public abstract class ReflectionUtils {
 	/**
 	 * Action to take on each method.
 	 */
+	@FunctionalInterface
 	public interface MethodCallback {
 
 		/**
@@ -768,6 +769,7 @@ public abstract class ReflectionUtils {
 	/**
 	 * Callback optionally used to filter methods to be operated on by a method callback.
 	 */
+	@FunctionalInterface
 	public interface MethodFilter {
 
 		/**
@@ -781,6 +783,7 @@ public abstract class ReflectionUtils {
 	/**
 	 * Callback interface invoked on each field in the hierarchy.
 	 */
+	@FunctionalInterface
 	public interface FieldCallback {
 
 		/**
@@ -794,6 +797,7 @@ public abstract class ReflectionUtils {
 	/**
 	 * Callback optionally used to filter fields to be operated on by a field callback.
 	 */
+	@FunctionalInterface
 	public interface FieldFilter {
 
 		/**

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2007 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.
@@ -26,6 +26,7 @@ package org.springframework.util;
  * @see org.springframework.beans.factory.config.BeanDefinitionVisitor#BeanDefinitionVisitor(StringValueResolver)
  * @see org.springframework.beans.factory.config.PropertyPlaceholderConfigurer
  */
+@FunctionalInterface
 public interface StringValueResolver {
 
 	/**

spring-core/src/main/java/org/springframework/util/backoff/BackOff.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.
@@ -43,6 +43,7 @@ package org.springframework.util.backoff;
  * @since 4.1
  * @see BackOffExecution
  */
+@FunctionalInterface
 public interface BackOff {
 
 	/**

spring-core/src/main/java/org/springframework/util/backoff/BackOffExecution.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 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.util.backoff;
  * @since 4.1
  * @see BackOff
  */
+@FunctionalInterface
 public interface BackOffExecution {
 
 	/**

spring-core/src/main/java/org/springframework/util/concurrent/FailureCallback.java

@@ -22,6 +22,7 @@ package org.springframework.util.concurrent;
  * @author Sebastien Deleuze
  * @since 4.1
  */
+@FunctionalInterface
 public interface FailureCallback {
 
 	/**

spring-core/src/main/java/org/springframework/util/concurrent/SuccessCallback.java

@@ -22,6 +22,7 @@ package org.springframework.util.concurrent;
  * @author Sebastien Deleuze
  * @since 4.1
  */
+@FunctionalInterface
 public interface SuccessCallback<T> {
 
 	/**