Log message for unused @ModelAttribute name

Closes gh-23877

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/method/annotation/ModelFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -24,6 +24,9 @@
 import java.util.Map;
 import java.util.Set;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
 import org.springframework.beans.BeanUtils;
 import org.springframework.core.Conventions;
 import org.springframework.core.GenericTypeResolver;
@@ -58,6 +61,9 @@
  */
 public final class ModelFactory {
 
+	private static final Log logger = LogFactory.getLog(ModelFactory.class);
+
+
 	private final List<ModelMethod> modelMethods = new ArrayList<>();
 
 	private final WebDataBinderFactory dataBinderFactory;
@@ -135,14 +141,22 @@ private void invokeModelAttributeMethods(NativeWebRequest request, ModelAndViewC
 			}
 
 			Object returnValue = modelMethod.invokeForRequest(request, container);
-			if (!modelMethod.isVoid()){
-				String returnValueName = getNameForReturnValue(returnValue, modelMethod.getReturnType());
-				if (!ann.binding()) {
-					container.setBindingDisabled(returnValueName);
-				}
-				if (!container.containsAttribute(returnValueName)) {
-					container.addAttribute(returnValueName, returnValue);
+			if (modelMethod.isVoid()) {
+				if (StringUtils.hasText(ann.value())) {
+					if (logger.isDebugEnabled()) {
+						logger.debug("Name in @ModelAttribute is ignored because method returns void: " +
+								modelMethod.getShortLogMessage());
+					}
 				}
+				continue;
+			}
+
+			String returnValueName = getNameForReturnValue(returnValue, modelMethod.getReturnType());
+			if (!ann.binding()) {
+				container.setBindingDisabled(returnValueName);
+			}
+			if (!container.containsAttribute(returnValueName)) {
+				container.addAttribute(returnValueName, returnValue);
 			}
 		}
 	}