WebMvc support for SSE Fragment stream

Closes gh-33194

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

@@ -0,0 +1,127 @@
+/*
+ * Copyright 2002-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.servlet.mvc.method.annotation;
+
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.support.ResourceBundleMessageSource;
+import org.springframework.core.MethodParameter;
+import org.springframework.core.ReactiveAdapterRegistry;
+import org.springframework.core.task.SyncTaskExecutor;
+import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
+import org.springframework.web.accept.ContentNegotiationManager;
+import org.springframework.web.context.request.NativeWebRequest;
+import org.springframework.web.context.request.ServletWebRequest;
+import org.springframework.web.context.request.async.AsyncWebRequest;
+import org.springframework.web.context.request.async.StandardServletAsyncWebRequest;
+import org.springframework.web.context.request.async.WebAsyncUtils;
+import org.springframework.web.method.support.ModelAndViewContainer;
+import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.servlet.view.script.ScriptTemplateConfigurer;
+import org.springframework.web.servlet.view.script.ScriptTemplateViewResolver;
+import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
+import org.springframework.web.testfixture.servlet.MockHttpServletResponse;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.web.testfixture.method.ResolvableMethod.on;
+
+/**
+ * Tests for streaming of {@link ModelAndView} fragments.
+ * @author Rossen Stoyanchev
+ */
+public class FragmentRenderingStreamTests {
+
+	@Test
+	void streamFragments() throws Exception {
+
+		AnnotationConfigApplicationContext context =
+				new AnnotationConfigApplicationContext(ScriptTemplatingConfiguration.class);
+
+		String prefix = "org/springframework/web/servlet/view/script/kotlin/";
+		ScriptTemplateViewResolver viewResolver = new ScriptTemplateViewResolver(prefix, ".kts");
+		viewResolver.setApplicationContext(context);
+
+		ResponseBodyEmitterReturnValueHandler handler = new ResponseBodyEmitterReturnValueHandler(
+				List.of(new MappingJackson2HttpMessageConverter()),
+				ReactiveAdapterRegistry.getSharedInstance(), new SyncTaskExecutor(),
+				new ContentNegotiationManager(),
+				List.of(viewResolver), null);
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		NativeWebRequest webRequest = new ServletWebRequest(request, response);
+
+		AsyncWebRequest asyncWebRequest = new StandardServletAsyncWebRequest(request, response);
+		WebAsyncUtils.getAsyncManager(webRequest).setAsyncWebRequest(asyncWebRequest);
+		request.setAsyncSupported(true);
+
+		MethodParameter type = on(TestController.class).resolveReturnType(SseEmitter.class);
+		SseEmitter emitter = new SseEmitter();
+		handler.handleReturnValue(emitter, type, new ModelAndViewContainer(), webRequest);
+
+		assertThat(request.isAsyncStarted()).isTrue();
+		assertThat(response.getStatus()).isEqualTo(200);
+
+		ModelAndView mav1 = new ModelAndView("fragment1", Map.of("foo", "Foo"));
+		ModelAndView mav2 = new ModelAndView("fragment2", Map.of("bar", "Bar"));
+
+		emitter.send(SseEmitter.event().data(mav1).data(mav2));
+
+		assertThat(response.getContentType()).isEqualTo("text/event-stream");
+		assertThat(response.getContentAsString()).isEqualTo(("""
+				data:<p>Hello Foo</p>
+				data:<p>Hello Bar</p>
+
+				"""));
+	}
+
+
+	private static class TestController {
+
+		SseEmitter handle() {
+			return null;
+		}
+	}
+
+
+	@Configuration
+	static class ScriptTemplatingConfiguration {
+
+		@Bean
+		ScriptTemplateConfigurer kotlinScriptConfigurer() {
+			ScriptTemplateConfigurer configurer = new ScriptTemplateConfigurer();
+			configurer.setEngineName("kotlin");
+			configurer.setScripts("org/springframework/web/servlet/view/script/kotlin/render.kts");
+			configurer.setRenderFunction("render");
+			return configurer;
+		}
+
+		@Bean
+		ResourceBundleMessageSource messageSource() {
+			ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
+			messageSource.setBasename("org/springframework/web/servlet/view/script/messages");
+			return messageSource;
+		}
+	}
+
+}