Move status/header handling into FragmentsRendering

Based on feedback from htmx-spring-boot. It's more generally useful
to process those from within DefaultFragmentsRendering rather than
in ModelAndViewMethodReturnValueHandler. That way a custom
return value handler can create a FragmentsRendering as well and
get the same result.

See gh-33194

Author: rstoyanchev

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

@@ -18,12 +18,8 @@
 
 import java.util.Collection;
 
-import jakarta.servlet.http.HttpServletResponse;
-
 import org.springframework.core.MethodParameter;
-import org.springframework.http.HttpHeaders;
 import org.springframework.lang.Nullable;
-import org.springframework.util.Assert;
 import org.springframework.util.PatternMatchUtils;
 import org.springframework.web.context.request.NativeWebRequest;
 import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
@@ -100,13 +96,6 @@ public void handleReturnValue(@Nullable Object returnValue, MethodParameter retu
 		}
 
 		if (returnValue instanceof FragmentsRendering rendering) {
-			mavContainer.setStatus(rendering.status());
-			HttpHeaders headers = rendering.headers();
-			if (!headers.isEmpty()) {
-				HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
-				Assert.state(response != null, "No HttpServletResponse");
-				headers.forEach((name, values) -> values.forEach(value -> response.addHeader(name, value)));
-			}
 			mavContainer.setView(rendering);
 			return;
 		}

spring-webmvc/src/main/java/org/springframework/web/servlet/view/DefaultFragmentsRendering.java

@@ -101,6 +101,14 @@ public void render(
 			@Nullable Map<String, ?> model, HttpServletRequest request, HttpServletResponse response)
 			throws Exception {
 
+		if (this.status != null) {
+			response.setStatus(this.status.value());
+		}
+
+		if (!this.headers.isEmpty()) {
+			this.headers.forEach((name, values) -> values.forEach(value -> response.addHeader(name, value)));
+		}
+
 		if (model != null) {
 			model.forEach((key, value) ->
 					this.modelAndViews.forEach(mv -> mv.getModel().putIfAbsent(key, value)));

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

@@ -91,13 +91,10 @@ void handleViewInstance() throws Exception {
 
 	@Test
 	void handleFragmentsRendering() throws Exception {
-		FragmentsRendering rendering = FragmentsRendering.with("viewName")
-				.header("headerName", "headerValue")
-				.build();
+		FragmentsRendering rendering = FragmentsRendering.with("viewName").build();
 
 		handler.handleReturnValue(rendering, returnParamModelAndView, mavContainer, webRequest);
 		assertThat(mavContainer.getView()).isInstanceOf(SmartView.class);
-		assertThat(this.webRequest.getResponse().getHeader("headerName")).isEqualTo("headerValue");
 	}
 
 	@Test

spring-webmvc/src/test/java/org/springframework/web/servlet/view/DefaultFragmentsRenderingTests.java

@@ -43,7 +43,6 @@
 @DisabledForJreRange(min = JAVA_21, disabledReason = "Kotlin doesn't support Java 21+ yet")
 public class DefaultFragmentsRenderingTests {
 
-
 	@Test
 	void render() throws Exception {
 
@@ -59,11 +58,13 @@ void render() throws Exception {
 
 		FragmentsRendering view = FragmentsRendering.with("fragment1", Map.of("foo", "Foo"))
 				.fragment("fragment2", Map.of("bar", "Bar"))
+				.header("headerName", "headerValue")
 				.build();
 
 		view.resolveNestedViews(viewResolver, Locale.ENGLISH);
 		view.render(Collections.emptyMap(), request, response);
 
+		assertThat(response.getHeader("headerName")).isEqualTo("headerValue");
 		assertThat(response.getContentAsString()).isEqualTo("""
 				<p>
 					Hello Foo