ConverterRegistry's addConverter declares generic type variables

Issue: SPR-12948

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2009 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.
@@ -27,18 +27,19 @@ public interface ConverterRegistry {
 
 	/**
 	 * Add a plain converter to this registry.
-	 * The convertible sourceType/targetType pair is derived from the Converter's parameterized types.
+	 * The convertible source/target type pair is derived from the Converter's parameterized types.
 	 * @throws IllegalArgumentException if the parameterized types could not be resolved
 	 */
 	void addConverter(Converter<?, ?> converter);
 
 	/**
 	 * Add a plain converter to this registry.
-	 * The convertible sourceType/targetType pair is specified explicitly.
-	 * Allows for a Converter to be reused for multiple distinct pairs without having to create a Converter class for each pair.
+	 * The convertible source/target type pair is specified explicitly.
+	 * <p>Allows for a Converter to be reused for multiple distinct pairs without
+	 * having to create a Converter class for each pair.
 	 * @since 3.1
 	 */
-	void addConverter(Class<?> sourceType, Class<?> targetType, Converter<?, ?> converter);
+	<S, T> void addConverter(Class<S> sourceType, Class<T> targetType, Converter<? super S, ? extends T> converter);
 
 	/**
 	 * Add a generic converter to this registry.
@@ -47,7 +48,7 @@ public interface ConverterRegistry {
 
 	/**
 	 * Add a ranged converter factory to this registry.
-	 * The convertible sourceType/rangeType pair is derived from the ConverterFactory's parameterized types.
+	 * The convertible source/target type pair is derived from the ConverterFactory's parameterized types.
 	 * @throws IllegalArgumentException if the parameterized types could not be resolved.
 	 */
 	void addConverterFactory(ConverterFactory<?, ?> converterFactory);

spring-core/src/main/java/org/springframework/core/convert/support/DefaultConversionService.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.
@@ -141,8 +141,7 @@ public class DefaultConversionService extends GenericConversionService {
 		converterRegistry.addConverter(Boolean.class, String.class, new ObjectToStringConverter());
 
 		converterRegistry.addConverterFactory(new StringToEnumConverterFactory());
-		converterRegistry.addConverter(Enum.class, String.class,
-				new EnumToStringConverter((ConversionService) converterRegistry));
+		converterRegistry.addConverter(new EnumToStringConverter((ConversionService) converterRegistry));
 
 		converterRegistry.addConverter(new StringToLocaleConverter());
 		converterRegistry.addConverter(Locale.class, String.class, new ObjectToStringConverter());

spring-core/src/main/java/org/springframework/core/convert/support/GenericConversionService.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.
@@ -103,7 +103,7 @@ public class GenericConversionService implements ConfigurableConversionService {
 	}
 
 	@Override
-	public void addConverter(Class<?> sourceType, Class<?> targetType, Converter<?, ?> converter) {
+	public <S, T> void addConverter(Class<S> sourceType, Class<T> targetType, Converter<? super S, ? extends T> converter) {
 		addConverter(new ConverterAdapter(
 				converter, ResolvableType.forClass(sourceType), ResolvableType.forClass(targetType)));
 	}