WebMvc support for SSE Fragment stream

Closes gh-33194

Author: rstoyanchev

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

@@ -18,6 +18,7 @@
 
 import java.lang.reflect.Method;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -32,7 +33,10 @@
 
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.beans.factory.BeanFactoryUtils;
 import org.springframework.beans.factory.InitializingBean;
+import org.springframework.beans.factory.ListableBeanFactory;
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.KotlinDetector;
@@ -41,6 +45,7 @@
 import org.springframework.core.ParameterNameDiscoverer;
 import org.springframework.core.ReactiveAdapterRegistry;
 import org.springframework.core.annotation.AnnotatedElementUtils;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.log.LogFormatUtils;
 import org.springframework.core.task.AsyncTaskExecutor;
 import org.springframework.core.task.SimpleAsyncTaskExecutor;
@@ -96,8 +101,11 @@
 import org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite;
 import org.springframework.web.method.support.InvocableHandlerMethod;
 import org.springframework.web.method.support.ModelAndViewContainer;
+import org.springframework.web.servlet.DispatcherServlet;
+import org.springframework.web.servlet.LocaleResolver;
 import org.springframework.web.servlet.ModelAndView;
 import org.springframework.web.servlet.View;
+import org.springframework.web.servlet.ViewResolver;
 import org.springframework.web.servlet.mvc.annotation.ModelAndViewResolver;
 import org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter;
 import org.springframework.web.servlet.mvc.support.RedirectAttributes;
@@ -767,7 +775,8 @@ private List<HandlerMethodReturnValueHandler> getDefaultReturnValueHandlers() {
 		handlers.add(new ModelMethodProcessor());
 		handlers.add(new ViewMethodReturnValueHandler());
 		handlers.add(new ResponseBodyEmitterReturnValueHandler(getMessageConverters(),
-				this.reactiveAdapterRegistry, this.taskExecutor, this.contentNegotiationManager));
+				this.reactiveAdapterRegistry, this.taskExecutor, this.contentNegotiationManager,
+				initViewResolvers(), initLocaleResolver()));
 		handlers.add(new StreamingResponseBodyReturnValueHandler());
 		handlers.add(new HttpEntityMethodProcessor(getMessageConverters(),
 				this.contentNegotiationManager, this.requestResponseBodyAdvice, this.errorResponseInterceptors));
@@ -801,6 +810,33 @@ private List<HandlerMethodReturnValueHandler> getDefaultReturnValueHandlers() {
 		return handlers;
 	}
 
+	private List<ViewResolver> initViewResolvers() {
+		if (getBeanFactory() instanceof ListableBeanFactory lbf) {
+			Map<String, ViewResolver> matchingBeans =
+					BeanFactoryUtils.beansOfTypeIncludingAncestors(lbf, ViewResolver.class, true, false);
+			if (!matchingBeans.isEmpty()) {
+				List<ViewResolver> viewResolvers = new ArrayList<>(matchingBeans.values());
+				AnnotationAwareOrderComparator.sort(viewResolvers);
+				return viewResolvers;
+			}
+		}
+		return Collections.emptyList();
+	}
+
+	@Nullable
+	private LocaleResolver initLocaleResolver() {
+		if (getBeanFactory() != null) {
+			try {
+				return getBeanFactory().getBean(
+						DispatcherServlet.LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);
+			}
+			catch (NoSuchBeanDefinitionException ex) {
+				// ignore
+			}
+		}
+		return null;
+	}
+
 	private static Predicate<MethodParameter> methodParamPredicate(
 			List<HandlerMethodArgumentResolver> resolvers, Class<?> resolverType) {