SPR-6464 Add 'setAlwaysUseRedirectAttributes' flag.

When set to 'true' the flag makes RedirectAttributes the only way to add 
attributes for a redirect thus ignoring the content of the default model 
even if RedirectAttributes is not in the list of controller method args.

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestMappingHandlerAdapter.java

@@ -40,6 +40,7 @@ import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.xml.SourceHttpMessageConverter;
 import org.springframework.http.converter.xml.XmlAwareFormHttpMessageConverter;
+import org.springframework.ui.Model;
 import org.springframework.ui.ModelMap;
 import org.springframework.util.ReflectionUtils.MethodFilter;
 import org.springframework.validation.DataBinder;
@@ -92,6 +93,7 @@ import org.springframework.web.servlet.mvc.method.annotation.support.ServletRequ
 import org.springframework.web.servlet.mvc.method.annotation.support.ServletResponseMethodArgumentResolver;
 import org.springframework.web.servlet.mvc.method.annotation.support.ViewMethodReturnValueHandler;
 import org.springframework.web.servlet.mvc.support.RedirectAttributes;
+import org.springframework.web.servlet.mvc.support.RedirectAttributesModelMap;
 import org.springframework.web.servlet.support.RequestContextUtils;
 import org.springframework.web.util.WebUtils;
 
@@ -145,6 +147,8 @@ public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter i
 
 	private SessionAttributeStore sessionAttributeStore = new DefaultSessionAttributeStore();
 	
+	private boolean alwaysUseRedirectAttributes;
+	
 	private final Map<Class<?>, SessionAttributesHandler> sessionAttributesHandlerCache =
 		new ConcurrentHashMap<Class<?>, SessionAttributesHandler>();
 
@@ -329,6 +333,22 @@ public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter i
 		this.parameterNameDiscoverer = parameterNameDiscoverer;
 	}
 	
+	/**
+	 * By default a controller uses {@link Model} to select attributes for 
+	 * rendering and for redirecting. However, a controller can also use 
+	 * {@link RedirectAttributes} to select attributes before a redirect.
+	 * <p>When this flag is set to {@code true}, {@link RedirectAttributes} 
+	 * becomes the only way to select attributes for a redirect. 
+	 * In other words, for a redirect a controller must use 
+	 * {@link RedirectAttributes} or no attributes will be used.
+	 * <p>The default value is {@code false}, meaning the {@link Model} is
+	 * used unless {@link RedirectAttributes} is used.
+	 * @see RedirectAttributes
+	 */
+	public void setAlwaysUseRedirectAttributes(boolean alwaysUseRedirectAttributes) {
+		this.alwaysUseRedirectAttributes = alwaysUseRedirectAttributes;
+	}
+
 	public void setBeanFactory(BeanFactory beanFactory) {
 		if (beanFactory instanceof ConfigurableBeanFactory) {
 			this.beanFactory = (ConfigurableBeanFactory) beanFactory;
@@ -510,13 +530,19 @@ public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter i
 			HandlerMethod handlerMethod) throws Exception {
 		
 		ServletWebRequest webRequest = new ServletWebRequest(request, response);
-		
-		ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod);
-		ModelFactory modelFactory = getModelFactory(handlerMethod);
+
+		WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
+		ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod, binderFactory);
+		ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
 
 		ModelAndViewContainer mavContainer = new ModelAndViewContainer();
 		mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
 		modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);
+
+		if (this.alwaysUseRedirectAttributes) {
+			DataBinder dataBinder = binderFactory.createBinder(webRequest, null, null);
+			mavContainer.setRedirectModel(new RedirectAttributesModelMap(dataBinder));
+		}
 		
 		SessionStatus sessionStatus = new SimpleSessionStatus();
 		
@@ -536,23 +562,23 @@ public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter i
 				Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
 				RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
 			}
-			return mav;				
+			return mav;
 		}
 	}
 
-	private ServletInvocableHandlerMethod createRequestMappingMethod(HandlerMethod handlerMethod) {
-		ServletInvocableHandlerMethod requestMappingMethod = 
-			new ServletInvocableHandlerMethod(handlerMethod.getBean(), handlerMethod.getMethod());
-		requestMappingMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
-		requestMappingMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
-		requestMappingMethod.setDataBinderFactory(getDataBinderFactory(handlerMethod));
-		requestMappingMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
-		return requestMappingMethod;
+	private ServletInvocableHandlerMethod createRequestMappingMethod(HandlerMethod handlerMethod, 
+																	 WebDataBinderFactory binderFactory) {
+		ServletInvocableHandlerMethod requestMethod;
+		requestMethod = new ServletInvocableHandlerMethod(handlerMethod.getBean(), handlerMethod.getMethod());
+		requestMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
+		requestMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
+		requestMethod.setDataBinderFactory(binderFactory);
+		requestMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
+		return requestMethod;
 	}
 	
-	private ModelFactory getModelFactory(HandlerMethod handlerMethod) {
+	private ModelFactory getModelFactory(HandlerMethod handlerMethod, WebDataBinderFactory binderFactory) {
 		SessionAttributesHandler sessionAttrHandler = getSessionAttributesHandler(handlerMethod);
-		WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
 		Class<?> handlerType = handlerMethod.getBeanType();
 		ModelFactory modelFactory = this.modelFactoryCache.get(handlerType);
 		if (modelFactory == null) {

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/method/annotation/support/RedirectAttributesMethodArgumentResolver.java

@@ -49,10 +49,16 @@ public class RedirectAttributesMethodArgumentResolver implements HandlerMethodAr
 								  ModelAndViewContainer mavContainer,
 								  NativeWebRequest webRequest, 
 								  WebDataBinderFactory binderFactory) throws Exception {
-		DataBinder dataBinder = binderFactory.createBinder(webRequest, null, null);
-		ModelMap attributes = new RedirectAttributesModelMap(dataBinder);
-		mavContainer.setRedirectModel(attributes);
-		return attributes;
+		
+		if (mavContainer.getRedirectModel() != null) {
+			return mavContainer.getRedirectModel();
+		}
+		else {
+			DataBinder dataBinder = binderFactory.createBinder(webRequest, null, null);
+			ModelMap redirectAttributes  = new RedirectAttributesModelMap(dataBinder);
+			mavContainer.setRedirectModel(redirectAttributes);
+			return redirectAttributes;
+		}
 	}
 
 }

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/method/annotation/support/ViewMethodReturnValueHandler.java

@@ -61,14 +61,14 @@ public class ViewMethodReturnValueHandler implements HandlerMethodReturnValueHan
 			String viewName = (String) returnValue;
 			mavContainer.setViewName(viewName);
 			if (isRedirectViewName(viewName)) {
-				mavContainer.setRedirectModelEnabled();
+				mavContainer.setUseRedirectModel();
 			}
 		}
 		else if (returnValue instanceof View){
 			View view = (View) returnValue;
 			mavContainer.setView(view);
 			if (isRedirectView(view)) {	
-				mavContainer.setRedirectModelEnabled();
+				mavContainer.setUseRedirectModel();
 			}
 		}
 		else {

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/support/RedirectAttributesModelMap.java

@@ -66,13 +66,14 @@ public class RedirectAttributesModelMap extends ModelMap implements RedirectAttr
 	 * <p>Formats the attribute value as a String before adding it.
 	 */
 	public RedirectAttributesModelMap addAttribute(String attributeName, Object attributeValue) {
-		if (attributeValue != null) {
-			super.addAttribute(attributeName, formatValue(attributeValue));
-		}
+		super.addAttribute(attributeName, formatValue(attributeValue));
 		return this;
 	}
 
 	private String formatValue(Object value) {
+		if (value == null) {
+			return null;
+		}
 		return (dataBinder != null) ? dataBinder.convertIfNecessary(value, String.class) : value.toString();
 	}
 
@@ -126,6 +127,28 @@ public class RedirectAttributesModelMap extends ModelMap implements RedirectAttr
 		return this;
 	}
 
+	/**
+	 * {@inheritDoc}
+	 * <p>The value is formatted as a String before being added.
+	 */
+	@Override
+	public Object put(String key, Object value) {
+		return super.put(key, formatValue(value));
+	}
+
+	/**
+	 * {@inheritDoc}
+	 * <p>Each value is formatted as a String before being added.
+	 */
+	@Override
+	public void putAll(Map<? extends String, ? extends Object> map) {
+		if (map != null) {
+			for (String key : map.keySet()) {
+				put(key, formatValue(map.get(key)));
+			}
+		}
+	}
+
 	public RedirectAttributes addFlashAttribute(String attributeName, Object attributeValue) {
 		this.flashAttributes.addAttribute(attributeName, attributeValue);
 		return this;