WebFlux supports field default/marker parameters for data classes as well

Issue: SPR-15871

Author: jhoeller

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ModelAttributeMethodArgumentResolver.java

@@ -112,7 +112,7 @@ public Mono<Object> resolveArgument(
 		ResolvableType valueType = (adapter != null ? type.getGeneric() : type);
 
 		Assert.state(adapter == null || !adapter.isMultiValue(),
-				() -> getClass().getSimpleName() + " doesn't support multi-value reactive type wrapper: " +
+				() -> getClass().getSimpleName() + " does not support multi-value reactive type wrapper: " +
 						parameter.getGenericParameterType());
 
 		String name = getAttributeName(parameter);
@@ -169,7 +169,7 @@ private Mono<?> prepareAttributeMono(String attributeName, ResolvableType attrib
 		if (attribute == null) {
 			Class<?> attributeClass = attributeType.getRawClass();
 			Assert.state(attributeClass != null, "No attribute class");
-			return createAttribute(attributeName,attributeClass , context, exchange);
+			return createAttribute(attributeName, attributeClass, context, exchange);
 		}
 
 		ReactiveAdapter adapterFrom = getAdapterRegistry().getAdapter(null, attribute);
@@ -230,9 +230,23 @@ private Mono<?> createAttribute(
 					() -> "Invalid number of parameter names: " + paramNames.length + " for constructor " + ctor);
 			Object[] args = new Object[paramTypes.length];
 			WebDataBinder binder = context.createDataBinder(exchange, null, attributeName);
+			String fieldDefaultPrefix = binder.getFieldDefaultPrefix();
+			String fieldMarkerPrefix = binder.getFieldMarkerPrefix();
 			for (int i = 0; i < paramNames.length; i++) {
-				Object value = bindValues.get(paramNames[i]);
-				value = (value != null && value instanceof List ? ((List<?>) value).toArray() : value);
+				String paramName = paramNames[i];
+				Class<?> paramType = paramTypes[i];
+				Object value = bindValues.get(paramName);
+				if (value == null) {
+					if (fieldDefaultPrefix != null) {
+						value = bindValues.get(fieldDefaultPrefix + paramName);
+					}
+					if (value == null && fieldMarkerPrefix != null) {
+						if (bindValues.get(fieldMarkerPrefix + paramName) != null) {
+							value = binder.getEmptyValue(paramType);
+						}
+					}
+				}
+				value = (value instanceof List ? ((List<?>) value).toArray() : value);
 				args[i] = binder.convertIfNecessary(value, paramTypes[i], new MethodParameter(ctor, i));
 			}
 			return BeanUtils.instantiateClass(ctor, args);

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/ModelAttributeMethodArgumentResolverTests.java

@@ -301,6 +301,8 @@ private void testBindBar(MethodParameter param) throws Exception {
 		assertTrue(map.get(bindingResultKey) instanceof BindingResult);
 	}
 
+	// TODO: SPR-15871, SPR-15542
+
 
 	private ModelAttributeMethodArgumentResolver createResolver() {
 		return new ModelAttributeMethodArgumentResolver(new ReactiveAdapterRegistry(), false);