Add API to register collection converters

Previously, the only way to add the collection converters to a registry
was to add *all* default converters. A new "addCollectionConverters"
public method is now available to only register them.

Issue: SPR-13618

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

@@ -88,6 +88,41 @@ public class DefaultConversionService extends GenericConversionService {
 		}
 	}
 
+	/**
+	 * Add collection converters.
+	 * @param converterRegistry the registry of converters to add to (must also be castable to ConversionService,
+	 * e.g. being a {@link ConfigurableConversionService})
+	 * @throws ClassCastException if the given ConverterRegistry could not be cast to a ConversionService
+	 * @since 4.2.3
+	 */
+	public static void addCollectionConverters(ConverterRegistry converterRegistry) {
+		ConversionService conversionService = (ConversionService) converterRegistry;
+
+		converterRegistry.addConverter(new ArrayToCollectionConverter(conversionService));
+		converterRegistry.addConverter(new CollectionToArrayConverter(conversionService));
+
+		converterRegistry.addConverter(new ArrayToArrayConverter(conversionService));
+		converterRegistry.addConverter(new CollectionToCollectionConverter(conversionService));
+		converterRegistry.addConverter(new MapToMapConverter(conversionService));
+
+		converterRegistry.addConverter(new ArrayToStringConverter(conversionService));
+		converterRegistry.addConverter(new StringToArrayConverter(conversionService));
+
+		converterRegistry.addConverter(new ArrayToObjectConverter(conversionService));
+		converterRegistry.addConverter(new ObjectToArrayConverter(conversionService));
+
+		converterRegistry.addConverter(new CollectionToStringConverter(conversionService));
+		converterRegistry.addConverter(new StringToCollectionConverter(conversionService));
+
+		converterRegistry.addConverter(new CollectionToObjectConverter(conversionService));
+		converterRegistry.addConverter(new ObjectToCollectionConverter(conversionService));
+
+		if (streamAvailable) {
+			converterRegistry.addConverter(new StreamConverter(conversionService));
+		}
+	}
+
+
 	// internal helpers
 
 	private static void addScalarConverters(ConverterRegistry converterRegistry) {
@@ -125,33 +160,6 @@ public class DefaultConversionService extends GenericConversionService {
 		converterRegistry.addConverter(UUID.class, String.class, new ObjectToStringConverter());
 	}
 
-	private static void addCollectionConverters(ConverterRegistry converterRegistry) {
-		ConversionService conversionService = (ConversionService) converterRegistry;
-
-		converterRegistry.addConverter(new ArrayToCollectionConverter(conversionService));
-		converterRegistry.addConverter(new CollectionToArrayConverter(conversionService));
-
-		converterRegistry.addConverter(new ArrayToArrayConverter(conversionService));
-		converterRegistry.addConverter(new CollectionToCollectionConverter(conversionService));
-		converterRegistry.addConverter(new MapToMapConverter(conversionService));
-
-		converterRegistry.addConverter(new ArrayToStringConverter(conversionService));
-		converterRegistry.addConverter(new StringToArrayConverter(conversionService));
-
-		converterRegistry.addConverter(new ArrayToObjectConverter(conversionService));
-		converterRegistry.addConverter(new ObjectToArrayConverter(conversionService));
-
-		converterRegistry.addConverter(new CollectionToStringConverter(conversionService));
-		converterRegistry.addConverter(new StringToCollectionConverter(conversionService));
-
-		converterRegistry.addConverter(new CollectionToObjectConverter(conversionService));
-		converterRegistry.addConverter(new ObjectToCollectionConverter(conversionService));
-
-		if (streamAvailable) {
-			converterRegistry.addConverter(new StreamConverter(conversionService));
-		}
-	}
-
 
 	/**
 	 * Inner class to avoid a hard-coded dependency on Java 8's {@code java.time} package.