ConversionService detects generic type declaration on target class behind proxy as well

Issue: SPR-14822
(cherry picked from commit f7d740f)

spring-core/src/main/java/org/springframework/core/convert/converter/ConverterFactory.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.
@@ -34,7 +34,7 @@ public interface ConverterFactory<S, R> {
 	 * Get the converter to convert from S to target type T, where T is also an instance of R.
 	 * @param <T> the target type
 	 * @param targetType the target type to convert to
-	 * @return A converter from S to T
+	 * @return a converter from S to T
 	 */
 	<T extends R> Converter<S, T> getConverter(Class<T> targetType);
 

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

@@ -49,12 +49,12 @@ public interface ConverterRegistry {
 	/**
 	 * Add a ranged converter factory to this registry.
 	 * The convertible source/target type pair is derived from the ConverterFactory's parameterized types.
-	 * @throws IllegalArgumentException if the parameterized types could not be resolved.
+	 * @throws IllegalArgumentException if the parameterized types could not be resolved
 	 */
-	void addConverterFactory(ConverterFactory<?, ?> converterFactory);
+	void addConverterFactory(ConverterFactory<?, ?> factory);
 
 	/**
-	 * Remove any converters from sourceType to targetType.
+	 * Remove any converters from {@code sourceType} to {@code targetType}.
 	 * @param sourceType the source type
 	 * @param targetType the target type
 	 */

spring-core/src/main/java/org/springframework/core/convert/support/GenericConversionService.java

@@ -27,6 +27,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
+import org.springframework.core.DecoratingProxy;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.convert.ConversionException;
 import org.springframework.core.convert.ConversionFailedException;
@@ -96,9 +97,14 @@ public class GenericConversionService implements ConfigurableConversionService {
 
 	@Override
 	public void addConverter(Converter<?, ?> converter) {
-		ResolvableType[] typeInfo = getRequiredTypeInfo(converter, Converter.class);
-		Assert.notNull(typeInfo, "Unable to the determine sourceType <S> and targetType " +
-				"<T> which your Converter<S, T> converts between; declare these generic types.");
+		ResolvableType[] typeInfo = getRequiredTypeInfo(converter.getClass(), Converter.class);
+		if (typeInfo == null && converter instanceof DecoratingProxy) {
+			typeInfo = getRequiredTypeInfo(((DecoratingProxy) converter).getDecoratedClass(), Converter.class);
+		}
+		if (typeInfo == null) {
+			throw new IllegalArgumentException("Unable to determine source type <S> and target type <T> for your " +
+					"Converter [" + converter.getClass().getName() + "]; does the class parameterize those types?");
+		}
 		addConverter(new ConverterAdapter(converter, typeInfo[0], typeInfo[1]));
 	}
 
@@ -115,11 +121,16 @@ public class GenericConversionService implements ConfigurableConversionService {
 	}
 
 	@Override
-	public void addConverterFactory(ConverterFactory<?, ?> converterFactory) {
-		ResolvableType[] typeInfo = getRequiredTypeInfo(converterFactory, ConverterFactory.class);
-		Assert.notNull(typeInfo, "Unable to the determine source type <S> and target range type R which your " +
-				"ConverterFactory<S, R> converts between; declare these generic types.");
-		addConverter(new ConverterFactoryAdapter(converterFactory,
+	public void addConverterFactory(ConverterFactory<?, ?> factory) {
+		ResolvableType[] typeInfo = getRequiredTypeInfo(factory.getClass(), ConverterFactory.class);
+		if (typeInfo == null && factory instanceof DecoratingProxy) {
+			typeInfo = getRequiredTypeInfo(((DecoratingProxy) factory).getDecoratedClass(), ConverterFactory.class);
+		}
+		if (typeInfo == null) {
+			throw new IllegalArgumentException("Unable to determine source type <S> and target type <T> for your " +
+					"ConverterFactory [" + factory.getClass().getName() + "]; does the class parameterize those types?");
+		}
+		addConverter(new ConverterFactoryAdapter(factory,
 				new ConvertiblePair(typeInfo[0].resolve(), typeInfo[1].resolve())));
 	}
 
@@ -284,8 +295,8 @@ public class GenericConversionService implements ConfigurableConversionService {
 
 	// Internal helpers
 
-	private ResolvableType[] getRequiredTypeInfo(Object converter, Class<?> genericIfc) {
-		ResolvableType resolvableType = ResolvableType.forClass(converter.getClass()).as(genericIfc);
+	private ResolvableType[] getRequiredTypeInfo(Class<?> converterClass, Class<?> genericIfc) {
+		ResolvableType resolvableType = ResolvableType.forClass(converterClass).as(genericIfc);
 		ResolvableType[] generics = resolvableType.getGenerics();
 		if (generics.length < 2) {
 			return null;