Ensure default value of @Payload required is enforced

When no @Payload is provided, it is equivalent to @Payload with default
attribute values. Since the default value of required=true, then
an argument that's not annotated is required.

spring-messaging/src/main/java/org/springframework/messaging/handler/annotation/support/MethodArgumentNotValidException.java

@@ -33,31 +33,61 @@ import org.springframework.validation.ObjectError;
 @SuppressWarnings("serial")
 public class MethodArgumentNotValidException extends MessagingException {
 
+	private final MethodParameter parameter;
+
+	private final BindingResult bindingResult;
+
+
 	/**
-	 * Create a new message with the given description.
-	 * @see #getMessage()
+	 * Create a new instance with the invalid {@code MethodParameter}.
 	 */
-	public MethodArgumentNotValidException(Message<?> message, String description) {
-		super(message, description);
+
+	public MethodArgumentNotValidException(Message<?> message, MethodParameter parameter) {
+		this(message, parameter, null);
 	}
 
 	/**
-	 * Create a new instance with a failed validation described by
-	 * the given {@link BindingResult}.
+	 * Create a new instance with the invalid {@code MethodParameter} and a
+	 * {@link org.springframework.validation.BindingResult}.
 	 */
-	public MethodArgumentNotValidException(Message<?> message,
-			MethodParameter parameter, BindingResult bindingResult) {
-		this(message, generateMessage(parameter, bindingResult));
+	public MethodArgumentNotValidException(Message<?> message, MethodParameter parameter,
+			BindingResult bindingResult) {
+
+		super(message, generateMessage(parameter, bindingResult));
+		this.parameter = parameter;
+		this.bindingResult = bindingResult;
 	}
 
+
+	/**
+	 * Return the MethodParameter that was rejected.
+	 */
+	public MethodParameter getMethodParameter() {
+		return this.parameter;
+	}
+
+	/**
+	 * Return the BindingResult if the failure is validation-related or {@code null}.
+	 */
+	public BindingResult getBindingResult() {
+		return this.bindingResult;
+	}
+
+
 	private static String generateMessage(MethodParameter parameter, BindingResult bindingResult) {
-		StringBuilder sb = new StringBuilder("Validation failed for parameter at index ")
+
+		StringBuilder sb = new StringBuilder("Invalid parameter at index ")
 				.append(parameter.getParameterIndex()).append(" in method: ")
-				.append(parameter.getMethod().toGenericString())
-				.append(", with ").append(bindingResult.getErrorCount()).append(" error(s): ");
-		for (ObjectError error : bindingResult.getAllErrors()) {
-			sb.append("[").append(error).append("] ");
+				.append(parameter.getMethod().toGenericString());
+
+
+		if (bindingResult != null) {
+			sb.append(", with ").append(bindingResult.getErrorCount()).append(" error(s): ");
+			for (ObjectError error : bindingResult.getAllErrors()) {
+				sb.append("[").append(error).append("] ");
+			}
 		}
+
 		return sb.toString();
 	}
 

spring-messaging/src/main/java/org/springframework/messaging/handler/annotation/support/PayloadArgumentResolver.java

@@ -27,6 +27,8 @@ import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.validation.BeanPropertyBindingResult;
+import org.springframework.validation.BindingResult;
+import org.springframework.validation.ObjectError;
 import org.springframework.validation.SmartValidator;
 import org.springframework.validation.Validator;
 
@@ -65,16 +67,21 @@ public class PayloadArgumentResolver implements HandlerMethodArgumentResolver {
 	}
 
 	@Override
-	public Object resolveArgument(MethodParameter parameter, Message<?> message) throws Exception {
-		Payload annot = parameter.getParameterAnnotation(Payload.class);
+	public Object resolveArgument(MethodParameter param, Message<?> message) throws Exception {
+
+		Payload annot = param.getParameterAnnotation(Payload.class);
 		if ((annot != null) && StringUtils.hasText(annot.value())) {
 			throw new IllegalStateException("@Payload SpEL expressions not supported by this resolver.");
 		}
 
-		Object target = getTargetPayload(parameter, message);
-		if (annot != null && isEmptyPayload(target)) {
-			if (annot.required()) {
-				throw new MethodArgumentNotValidException(message, createPayloadRequiredExceptionMessage(parameter, target));
+		Object target = getTargetPayload(param, message);
+		if (isEmptyPayload(target)) {
+			if (annot == null || annot.required()) {
+				String paramName = param.getParameterName();
+				paramName = (paramName == null ? "Arg" + param.getParameterIndex() : paramName);
+				BindingResult bindingResult = new BeanPropertyBindingResult(target, paramName);
+				bindingResult.addError(new ObjectError(paramName, "@Payload param is required"));
+				throw new MethodArgumentNotValidException(message, param, bindingResult);
 			}
 			else {
 				return null;
@@ -82,17 +89,18 @@ public class PayloadArgumentResolver implements HandlerMethodArgumentResolver {
 		}
 
 		if (annot != null) { // Only validate @Payload
-			validate(message, parameter, target);
+			validate(message, param, target);
 		}
 		return target;
 	}
 
 	/**
-	 * Return the target payload to handle for the specified message. Can either
-	 * be the payload itself if the parameter type supports it or the converted
-	 * one otherwise. While the payload of a {@link Message} cannot be null by
-	 * design, this method may return a {@code null} payload if the conversion
-	 * result is {@code null}.
+	 * Return the payload for the specified message, which can be the payload
+	 * itself if it matches the parameter type or the result of message conversion
+	 * otherwise.
+	 *
+	 * <p>While the payload of a {@link Message} cannot be {@code null} by design,
+	 * this method may return {@code null} if the message converter returns that.
 	 */
 	protected Object getTargetPayload(MethodParameter parameter, Message<?> message) {
 		Class<?> sourceClass = message.getPayload().getClass();
@@ -146,19 +154,4 @@ public class PayloadArgumentResolver implements HandlerMethodArgumentResolver {
 		}
 	}
 
-	private String createPayloadRequiredExceptionMessage(MethodParameter parameter, Object payload) {
-		String name = parameter.getParameterName() != null
-				? parameter.getParameterName() : "arg" + parameter.getParameterIndex();
-		StringBuilder sb = new StringBuilder("Payload parameter '").append(name)
-				.append(" at index ").append(parameter.getParameterIndex()).append(" ");
-		if (payload == null) {
-			sb.append("could not be converted to '").append(parameter.getParameterType().getName())
-					.append("' and is required");
-		}
-		else {
-			sb.append("is required");
-		}
-		return sb.toString();
-	}
-
 }