Allow RedirectAttributes on ExceptionHandlers

Prior to this commit, `@ExceptionHandler` methods could not be injected
with `RedirectAttributes` arguments. This would make it impossible to
handle an error by redirecting to another view and add flashmap
attributes, to be included in the model when the next view is called.

Here is an example:

```
@ExceptionHandler(MyException.class)
public String handleException(MyException ex, RedirectAttributes
    redirectAttributes) {

  redirectAttributes.addFlashAttribute("errorMessage",
      "This is an error message");
  return "redirect:/";
}
```

This commit adds a new `RedirectAttributesMethodArgumentResolver`
instance in the list of pre-configured `HandlerMethodArgumentResolver`
in `ExceptionHandlerExceptionResolver`.

Issue: SPR-14651

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ExceptionHandlerExceptionResolver.java

@@ -55,6 +55,8 @@ import org.springframework.web.method.support.ModelAndViewContainer;
 import org.springframework.web.servlet.ModelAndView;
 import org.springframework.web.servlet.View;
 import org.springframework.web.servlet.handler.AbstractHandlerMethodExceptionResolver;
+import org.springframework.web.servlet.mvc.support.RedirectAttributes;
+import org.springframework.web.servlet.support.RequestContextUtils;
 
 /**
  * An {@link AbstractHandlerMethodExceptionResolver} that resolves exceptions
@@ -303,6 +305,7 @@ public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExce
 		// Type-based argument resolution
 		resolvers.add(new ServletRequestMethodArgumentResolver());
 		resolvers.add(new ServletResponseMethodArgumentResolver());
+		resolvers.add(new RedirectAttributesMethodArgumentResolver());
 		resolvers.add(new ModelMethodProcessor());
 
 		// Custom arguments
@@ -401,6 +404,11 @@ public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExce
 			if (!mavContainer.isViewReference()) {
 				mav.setView((View) mavContainer.getView());
 			}
+			if (model instanceof RedirectAttributes) {
+				Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
+				request = webRequest.getNativeRequest(HttpServletRequest.class);
+				RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
+			}
 			return mav;
 		}
 	}

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RedirectAttributesMethodArgumentResolver.java

@@ -53,8 +53,14 @@ public class RedirectAttributesMethodArgumentResolver implements HandlerMethodAr
 	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
 			NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
 
-		DataBinder dataBinder = binderFactory.createBinder(webRequest, null, null);
-		ModelMap redirectAttributes  = new RedirectAttributesModelMap(dataBinder);
+		ModelMap redirectAttributes;
+		if(binderFactory != null) {
+			DataBinder dataBinder = binderFactory.createBinder(webRequest, null, null);
+			redirectAttributes  = new RedirectAttributesModelMap(dataBinder);
+		}
+		else {
+			redirectAttributes  = new RedirectAttributesModelMap();
+		}
 		mavContainer.setRedirectModel(redirectAttributes);
 		return redirectAttributes;
 	}

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ExceptionHandlerExceptionResolverTests.java

@@ -42,7 +42,10 @@ import org.springframework.web.method.HandlerMethod;
 import org.springframework.web.method.annotation.ModelMethodProcessor;
 import org.springframework.web.method.support.HandlerMethodArgumentResolver;
 import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
+import org.springframework.web.servlet.DispatcherServlet;
+import org.springframework.web.servlet.FlashMap;
 import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 import org.springframework.web.util.NestedServletException;
 
 import static org.junit.Assert.*;
@@ -53,6 +56,7 @@ import static org.junit.Assert.*;
  * @author Rossen Stoyanchev
  * @author Arjen Poutsma
  * @author Kazuki Shimizu
+ * @author Brian Clozel
  * @since 3.1
  */
 @SuppressWarnings("unused")
@@ -82,6 +86,7 @@ public class ExceptionHandlerExceptionResolverTests {
 		this.resolver = new ExceptionHandlerExceptionResolver();
 		this.resolver.setWarnLogCategory(this.resolver.getClass().getName());
 		this.request = new MockHttpServletRequest("GET", "/");
+		this.request.setAttribute(DispatcherServlet.OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
 		this.response = new MockHttpServletResponse();
 	}
 
@@ -192,6 +197,20 @@ public class ExceptionHandlerExceptionResolverTests {
 		assertEquals("IllegalArgumentException", mav.getModelMap().get("exceptionClassName"));
 	}
 
+	@Test  // SPR-14651
+	public void resolveRedirectAttributesAtArgument() throws Exception {
+		IllegalArgumentException ex = new IllegalArgumentException();
+		HandlerMethod handlerMethod = new HandlerMethod(new RedirectAttributesController(), "handle");
+		this.resolver.afterPropertiesSet();
+		ModelAndView mav = this.resolver.resolveException(this.request, this.response, handlerMethod, ex);
+
+		assertNotNull(mav);
+		assertEquals("redirect:/", mav.getViewName());
+		FlashMap flashMap = (FlashMap) this.request.getAttribute(DispatcherServlet.OUTPUT_FLASH_MAP_ATTRIBUTE);
+		assertNotNull("output FlashMap should exist", flashMap);
+		assertEquals("IllegalArgumentException", flashMap.get("exceptionClassName"));
+	}
+
 	@Test
 	public void resolveExceptionGlobalHandler() throws Exception {
 		AnnotationConfigApplicationContext cxt = new AnnotationConfigApplicationContext(MyConfig.class);
@@ -364,6 +383,18 @@ public class ExceptionHandlerExceptionResolverTests {
 		}
 	}
 
+	@Controller
+	static class RedirectAttributesController {
+
+		public void handle() {}
+
+		@ExceptionHandler
+		public String handleException(Exception ex, RedirectAttributes redirectAttributes) {
+			redirectAttributes.addFlashAttribute("exceptionClassName", ClassUtils.getShortName(ex.getClass()));
+			return "redirect:/";
+		}
+	}
+
 
 	@RestControllerAdvice
 	@Order(1)