Allow Errors after @RequestBody and @RequestPart

An @RequestBody or an @RequestPart argument can now be followed by an
Errors/BindingResult argument making it possible to handle validation
errors (as a result of an @Valid annotation) locally within the
@RequestMapping method.

Issue: SPR-7114

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

@@ -38,8 +38,8 @@ import org.springframework.web.context.request.NativeWebRequest;
 import org.springframework.web.method.support.HandlerMethodArgumentResolver;
 
 /**
- * A base class for resolving method argument values by reading from the body of a request 
- * with {@link HttpMessageConverter}s.
+ * A base class for resolving method argument values by reading from the body of
+ * a request with {@link HttpMessageConverter}s.
  *
  * @author Arjen Poutsma
  * @author Rossen Stoyanchev
@@ -48,9 +48,9 @@ import org.springframework.web.method.support.HandlerMethodArgumentResolver;
 public abstract class AbstractMessageConverterMethodArgumentResolver implements HandlerMethodArgumentResolver {
 
 	protected final Log logger = LogFactory.getLog(getClass());
-	
+
 	protected final List<HttpMessageConverter<?>> messageConverters;
-	
+
 	protected final List<MediaType> allSupportedMediaTypes;
 
 	public AbstractMessageConverterMethodArgumentResolver(List<HttpMessageConverter<?>> messageConverters) {
@@ -60,8 +60,8 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 	}
 
 	/**
-	 * Returns the media types supported by all provided message converters preserving their ordering and 
-	 * further sorting by specificity via {@link MediaType#sortBySpecificity(List)}. 
+	 * Return the media types supported by all provided message converters sorted
+	 * by specificity via {@link MediaType#sortBySpecificity(List)}.
 	 */
 	private static List<MediaType> getAllSupportedMediaTypes(List<HttpMessageConverter<?>> messageConverters) {
 		Set<MediaType> allSupportedMediaTypes = new LinkedHashSet<MediaType>();
@@ -72,11 +72,12 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 		MediaType.sortBySpecificity(result);
 		return Collections.unmodifiableList(result);
 	}
-	
+
 	/**
-	 * Creates the method argument value of the expected parameter type by reading from the given request.
-	 * 
-	 * @param <T> the expected type of the argument value to be created 
+	 * Creates the method argument value of the expected parameter type by
+	 * reading from the given request.
+	 *
+	 * @param <T> the expected type of the argument value to be created
 	 * @param webRequest the current request
 	 * @param methodParam the method argument
 	 * @param paramType the type of the argument value to be created
@@ -86,15 +87,16 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 	 */
 	protected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter methodParam, Class<T> paramType) throws IOException,
 			HttpMediaTypeNotSupportedException {
-			
-				HttpInputMessage inputMessage = createInputMessage(webRequest);
-				return readWithMessageConverters(inputMessage, methodParam, paramType);
-			}
+
+		HttpInputMessage inputMessage = createInputMessage(webRequest);
+		return readWithMessageConverters(inputMessage, methodParam, paramType);
+	}
 
 	/**
-	 * Creates the method argument value of the expected parameter type by reading from the given HttpInputMessage. 
-	 * 
-	 * @param <T> the expected type of the argument value to be created 
+	 * Creates the method argument value of the expected parameter type by reading
+	 * from the given HttpInputMessage.
+	 *
+	 * @param <T> the expected type of the argument value to be created
 	 * @param inputMessage the HTTP input message representing the current request
 	 * @param methodParam the method argument
 	 * @param paramType the type of the argument value to be created
@@ -103,14 +105,14 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 	 * @throws HttpMediaTypeNotSupportedException if no suitable message converter is found
 	 */
 	@SuppressWarnings("unchecked")
-	protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter methodParam, Class<T> paramType) throws IOException,
-			HttpMediaTypeNotSupportedException {
-			
+	protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter methodParam,
+			Class<T> paramType) throws IOException, HttpMediaTypeNotSupportedException {
+
 				MediaType contentType = inputMessage.getHeaders().getContentType();
 				if (contentType == null) {
 					contentType = MediaType.APPLICATION_OCTET_STREAM;
 				}
-			
+
 				for (HttpMessageConverter<?> messageConverter : this.messageConverters) {
 					if (messageConverter.canRead(paramType, contentType)) {
 						if (logger.isDebugEnabled()) {
@@ -120,7 +122,7 @@ public abstract class AbstractMessageConverterMethodArgumentResolver implements
 						return ((HttpMessageConverter<T>) messageConverter).read(paramType, inputMessage);
 					}
 				}
-			
+
 				throw new HttpMediaTypeNotSupportedException(contentType, allSupportedMediaTypes);
 			}
 

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

@@ -28,6 +28,7 @@ import org.springframework.http.HttpInputMessage;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.util.Assert;
 import org.springframework.validation.BindingResult;
+import org.springframework.validation.Errors;
 import org.springframework.web.bind.MethodArgumentNotValidException;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.bind.annotation.RequestBody;
@@ -49,26 +50,26 @@ import org.springframework.web.util.WebUtils;
  * Resolves the following method arguments:
  * <ul>
  * 	<li>Annotated with {@code @RequestPart}
- * 	<li>Of type {@link MultipartFile} in conjunction with Spring's 
+ * 	<li>Of type {@link MultipartFile} in conjunction with Spring's
  *  {@link MultipartResolver} abstraction
- * 	<li>Of type {@code javax.servlet.http.Part} in conjunction with 
+ * 	<li>Of type {@code javax.servlet.http.Part} in conjunction with
  * 	Servlet 3.0 multipart requests
  * </ul>
- * 
- * <p>When a parameter is annotated with {@code @RequestPart} the content of the 
- * part is passed through an {@link HttpMessageConverter} to resolve the method 
- * argument with the 'Content-Type' of the request part in mind. This is 
+ *
+ * <p>When a parameter is annotated with {@code @RequestPart} the content of the
+ * part is passed through an {@link HttpMessageConverter} to resolve the method
+ * argument with the 'Content-Type' of the request part in mind. This is
  * analogous to what @{@link RequestBody} does to resolve an argument based on
  * the content of a regular request.
- * 
- * <p>When a parameter is not annotated or the name of the part is not specified, 
+ *
+ * <p>When a parameter is not annotated or the name of the part is not specified,
  * it is derived from the name of the method argument.
- * 
- * <p>Automatic validation may be applied if the argument is annotated with 
- * {@code @javax.validation.Valid}. In case of validation failure, a 
+ *
+ * <p>Automatic validation may be applied if the argument is annotated with
+ * {@code @javax.validation.Valid}. In case of validation failure, a
  * {@link MethodArgumentNotValidException} is raised and a 400 response status
  * code returned if {@link DefaultHandlerExceptionResolver} is configured.
- * 
+ *
  * @author Rossen Stoyanchev
  * @since 3.1
  */
@@ -111,8 +112,8 @@ public class RequestPartMethodArgumentResolver extends AbstractMessageConverterM
 
 		HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);
 		assertIsMultipartRequest(servletRequest);
-		
-		MultipartHttpServletRequest multipartRequest = 
+
+		MultipartHttpServletRequest multipartRequest =
 			WebUtils.getNativeRequest(servletRequest, MultipartHttpServletRequest.class);
 
 		String partName = getPartName(parameter);
@@ -133,20 +134,11 @@ public class RequestPartMethodArgumentResolver extends AbstractMessageConverterM
 			try {
 				HttpInputMessage inputMessage = new RequestPartServletServerHttpRequest(servletRequest, partName);
 				arg = readWithMessageConverters(inputMessage, parameter, parameter.getParameterType());
+				WebDataBinder binder = binderFactory.createBinder(request, arg, partName);
 				if (arg != null) {
-					Annotation[] annotations = parameter.getParameterAnnotations();
-					for (Annotation annot : annotations) {
-						if (annot.annotationType().getSimpleName().startsWith("Valid")) {
-							WebDataBinder binder = binderFactory.createBinder(request, arg, partName);
-							Object hints = AnnotationUtils.getValue(annot);
-							binder.validate(hints instanceof Object[] ? (Object[]) hints : new Object[] {hints});
-							BindingResult bindingResult = binder.getBindingResult();
-							if (bindingResult.hasErrors()) {
-								throw new MethodArgumentNotValidException(parameter, bindingResult);
-							}
-						}
-					}
+					validate(binder, parameter);
 				}
+				mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + partName, binder.getBindingResult());
 			}
 			catch (MissingServletRequestPartException ex) {
 				// handled below
@@ -160,7 +152,7 @@ public class RequestPartMethodArgumentResolver extends AbstractMessageConverterM
 		if (arg == null && isRequired) {
 			throw new MissingServletRequestPartException(partName);
 		}
-		
+
 		return arg;
 	}
 
@@ -170,7 +162,7 @@ public class RequestPartMethodArgumentResolver extends AbstractMessageConverterM
 			throw new MultipartException("The current request is not a multipart request");
 		}
 	}
-	
+
 	private String getPartName(MethodParameter parameter) {
 		RequestPart annot = parameter.getParameterAnnotation(RequestPart.class);
 		String partName = (annot != null) ? annot.value() : "";
@@ -181,7 +173,7 @@ public class RequestPartMethodArgumentResolver extends AbstractMessageConverterM
 		}
 		return partName;
 	}
-	
+
 	private boolean isMultipartFileCollection(MethodParameter parameter) {
 		Class<?> paramType = parameter.getParameterType();
 		if (Collection.class.equals(paramType) || List.class.isAssignableFrom(paramType)){
@@ -193,4 +185,35 @@ public class RequestPartMethodArgumentResolver extends AbstractMessageConverterM
 		return false;
 	}
 
+	private void validate(WebDataBinder binder, MethodParameter parameter) throws MethodArgumentNotValidException {
+
+		Annotation[] annotations = parameter.getParameterAnnotations();
+		for (Annotation annot : annotations) {
+			if (annot.annotationType().getSimpleName().startsWith("Valid")) {
+				Object hints = AnnotationUtils.getValue(annot);
+				binder.validate(hints instanceof Object[] ? (Object[]) hints : new Object[] {hints});
+				BindingResult bindingResult = binder.getBindingResult();
+				if (bindingResult.hasErrors()) {
+					if (isBindExceptionRequired(binder, parameter)) {
+						throw new MethodArgumentNotValidException(parameter, bindingResult);
+					}
+				}
+			}
+		}
+	}
+
+	/**
+	 * Whether to raise a {@link MethodArgumentNotValidException} on validation errors.
+	 * @param binder the data binder used to perform data binding
+	 * @param parameter the method argument
+	 * @return {@code true} if the next method argument is not of type {@link Errors}.
+	 */
+	private boolean isBindExceptionRequired(WebDataBinder binder, MethodParameter parameter) {
+		int i = parameter.getParameterIndex();
+		Class<?>[] paramTypes = parameter.getMethod().getParameterTypes();
+		boolean hasBindingResult = (paramTypes.length > (i + 1) && Errors.class.isAssignableFrom(paramTypes[i + 1]));
+
+		return !hasBindingResult;
+	}
+
 }

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

@@ -27,6 +27,7 @@ import org.springframework.http.HttpInputMessage;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.HttpMessageNotReadableException;
 import org.springframework.validation.BindingResult;
+import org.springframework.validation.Errors;
 import org.springframework.web.HttpMediaTypeNotAcceptableException;
 import org.springframework.web.HttpMediaTypeNotSupportedException;
 import org.springframework.web.accept.ContentNegotiationManager;
@@ -85,33 +86,52 @@ public class RequestResponseBodyMethodProcessor extends AbstractMessageConverter
 	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
 			NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
 
-		Object arg = readWithMessageConverters(webRequest, parameter, parameter.getParameterType());
-		validate(parameter, webRequest, binderFactory, arg);
-		return arg;
+		Object argument = readWithMessageConverters(webRequest, parameter, parameter.getParameterType());
+
+		String name = Conventions.getVariableNameForParameter(parameter);
+		WebDataBinder binder = binderFactory.createBinder(webRequest, argument, name);
+
+		if (argument != null) {
+			validate(binder, parameter);
+		}
+
+		mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());
+
+		return argument;
 	}
 
-	private void validate(MethodParameter parameter, NativeWebRequest webRequest,
-			WebDataBinderFactory binderFactory, Object arg) throws Exception, MethodArgumentNotValidException {
+	private void validate(WebDataBinder binder, MethodParameter parameter) throws Exception, MethodArgumentNotValidException {
 
-		if (arg == null) {
-			return;
-		}
 		Annotation[] annotations = parameter.getParameterAnnotations();
 		for (Annotation annot : annotations) {
-			if (!annot.annotationType().getSimpleName().startsWith("Valid")) {
-				continue;
-			}
-			String name = Conventions.getVariableNameForParameter(parameter);
-			WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);
-			Object hints = AnnotationUtils.getValue(annot);
-			binder.validate(hints instanceof Object[] ? (Object[]) hints : new Object[] {hints});
-			BindingResult bindingResult = binder.getBindingResult();
-			if (bindingResult.hasErrors()) {
-				throw new MethodArgumentNotValidException(parameter, bindingResult);
+			if (annot.annotationType().getSimpleName().startsWith("Valid")) {
+				Object hints = AnnotationUtils.getValue(annot);
+				binder.validate(hints instanceof Object[] ? (Object[]) hints : new Object[] {hints});
+				BindingResult bindingResult = binder.getBindingResult();
+				if (bindingResult.hasErrors()) {
+					if (isBindExceptionRequired(binder, parameter)) {
+						throw new MethodArgumentNotValidException(parameter, bindingResult);
+					}
+				}
+				break;
 			}
 		}
 	}
 
+	/**
+	 * Whether to raise a {@link MethodArgumentNotValidException} on validation errors.
+	 * @param binder the data binder used to perform data binding
+	 * @param parameter the method argument
+	 * @return {@code true} if the next method argument is not of type {@link Errors}.
+	 */
+	private boolean isBindExceptionRequired(WebDataBinder binder, MethodParameter parameter) {
+		int i = parameter.getParameterIndex();
+		Class<?>[] paramTypes = parameter.getMethod().getParameterTypes();
+		boolean hasBindingResult = (paramTypes.length > (i + 1) && Errors.class.isAssignableFrom(paramTypes[i + 1]));
+
+		return !hasBindingResult;
+	}
+
 	@Override
 	protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage,
 			MethodParameter methodParam, Class<T> paramType) throws IOException, HttpMediaTypeNotSupportedException {