sync springdoc#2291 and clear logic for flat parameter object

Author: eshizhan

springdoc-openapi-common/src/main/java/org/springdoc/core/DelegatingMethodParameter.java

@@ -21,33 +21,24 @@
  */
 package org.springdoc.core;
 
-import java.lang.annotation.Annotation;
-import java.lang.reflect.AnnotatedElement;
-import java.lang.reflect.Constructor;
-import java.lang.reflect.Executable;
-import java.lang.reflect.Field;
-import java.lang.reflect.Member;
-import java.lang.reflect.Method;
-import java.lang.reflect.Type;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.List;
-import java.util.Objects;
-import java.util.Optional;
-
 import org.apache.commons.lang3.ArrayUtils;
 import org.apache.commons.lang3.reflect.FieldUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springdoc.api.annotations.ParameterObject;
 import org.springdoc.core.converters.AdditionalModelsConverter;
 import org.springdoc.core.customizers.DelegatingMethodParameterCustomizer;
-
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ParameterNameDiscoverer;
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestPart;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.*;
+import java.util.*;
 
 /**
  * The type Delegating method parameter.
@@ -119,19 +110,16 @@ public static MethodParameter[] customize(String[] pNames, MethodParameter[] par
 			MethodParameter p = parameters[i];
 			Class<?> paramClass = AdditionalModelsConverter.getParameterObjectReplacement(p.getParameterType());
 
-			if (!MethodParameterPojoExtractor.isSimpleType(paramClass) && (p.hasParameterAnnotation(ParameterObject.class) || AnnotatedElementUtils.isAnnotated(paramClass, ParameterObject.class))) {
+			boolean hasFlatAnnotation = p.hasParameterAnnotation(ParameterObject.class) || AnnotatedElementUtils.isAnnotated(paramClass, ParameterObject.class);
+			boolean hasNotFlatAnnotation = Arrays.stream(p.getParameterAnnotations())
+					.anyMatch(annotation -> Arrays.asList(RequestBody.class, RequestPart.class).contains(annotation.annotationType()));
+			if (!MethodParameterPojoExtractor.isSimpleType(paramClass)
+				&& (hasFlatAnnotation || (defaultFlatParamObject && !hasNotFlatAnnotation && !AbstractRequestService.isRequestTypeToIgnore(paramClass)))) {
 				MethodParameterPojoExtractor.extractFrom(paramClass).forEach(methodParameter -> {
 					optionalDelegatingMethodParameterCustomizer.ifPresent(customizer -> customizer.customize(p, methodParameter));
 					explodedParameters.add(methodParameter);
 				});
 			}
-			else if (defaultFlatParamObject && !MethodParameterPojoExtractor.isSimpleType(paramClass) && !AbstractRequestService.isRequestTypeToIgnore(paramClass)) {
-				MethodParameterPojoExtractor.extractFrom(paramClass).forEach(methodParameter -> {
-					optionalDelegatingMethodParameterCustomizer
-							.ifPresent(customizer -> customizer.customize(p, methodParameter));
-					explodedParameters.add(methodParameter);
-				});
-			}
 			else {
 				String name = pNames != null ? pNames[i] : p.getParameterName();
 				explodedParameters.add(new DelegatingMethodParameter(p, name, null, false, false));