Improve HandlerMethod#resolvedFromHandlerMethod initialization

Ensure the original instance is always the one returned no matter how
many times the HandlerMethod is re-created.

Make the constructor protected to allow subclasses to re-create the
HandlerMethod as the concrete subclass.

See spring-projectsgh-34375

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/method/HandlerMethod.java

@@ -181,9 +181,13 @@ protected HandlerMethod(HandlerMethod handlerMethod) {
 	}
 
 	/**
-	 * Re-create HandlerMethod with additional input.
+	 * Re-create new HandlerMethod instance that copies the given HandlerMethod
+	 * but replaces the handler, and optionally checks for the presence of
+	 * validation annotations.
+	 * <p>Subclasses can override this to ensure that a HandlerMethod is of the
+	 * same type if re-created.
 	 */
-	private HandlerMethod(HandlerMethod handlerMethod, @Nullable Object handler, boolean initValidateFlags) {
+	protected HandlerMethod(HandlerMethod handlerMethod, @Nullable Object handler, boolean initValidateFlags) {
 		super(handlerMethod);
 		this.bean = (handler != null ? handler : handlerMethod.bean);
 		this.beanFactory = handlerMethod.beanFactory;
@@ -197,7 +201,8 @@ private HandlerMethod(HandlerMethod handlerMethod, @Nullable Object handler, boo
 				handlerMethod.validateReturnValue);
 		this.responseStatus = handlerMethod.responseStatus;
 		this.responseStatusReason = handlerMethod.responseStatusReason;
-		this.resolvedFromHandlerMethod = handlerMethod;
+		this.resolvedFromHandlerMethod = (handlerMethod.resolvedFromHandlerMethod != null ?
+				handlerMethod.resolvedFromHandlerMethod : handlerMethod);
 		this.description = handlerMethod.toString();
 	}
 

spring-web/src/test/java/org/springframework/web/method/HandlerMethodTests.java

@@ -25,6 +25,7 @@
 import jakarta.validation.constraints.Size;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.context.support.StaticApplicationContext;
 import org.springframework.util.ClassUtils;
 import org.springframework.validation.annotation.Validated;
 
@@ -79,6 +80,23 @@ void createWithResolvedBeanSameInstance() {
 		assertThat(handlerMethod.createWithResolvedBean()).isSameAs(handlerMethod);
 	}
 
+	@Test
+	void resolvedFromHandlerMethod() {
+		StaticApplicationContext context = new StaticApplicationContext();
+		context.registerSingleton("myClass", MyClass.class);
+
+		MyClass target = new MyClass();
+		Method method = ClassUtils.getMethod(target.getClass(), "addPerson", (Class<?>[]) null);
+
+		HandlerMethod hm1 = new HandlerMethod("myClass", context.getBeanFactory(), method);
+		HandlerMethod hm2 = hm1.createWithValidateFlags();
+		HandlerMethod hm3 = hm2.createWithResolvedBean();
+
+		assertThat(hm1.getResolvedFromHandlerMethod()).isNull();
+		assertThat(hm2.getResolvedFromHandlerMethod()).isSameAs(hm1);
+		assertThat(hm3.getResolvedFromHandlerMethod()).isSameAs(hm1);
+	}
+
 	private static void testValidateArgs(Object target, List<String> methodNames, boolean expected) {
 		for (String methodName : methodNames) {
 			assertThat(getHandlerMethod(target, methodName).shouldValidateArguments()).isEqualTo(expected);