Improve resolution of multi-value async model attrs

Multi-value async attributes like Flux and Observable in the model
are treated with Collection semantics and resolved to Mono<List<?>>
prior to rendering.

spring-web-reactive/src/main/java/org/springframework/web/reactive/result/view/ViewResolutionResultHandler.java

@@ -294,13 +294,20 @@ public class ViewResolutionResultHandler extends AbstractHandlerResultHandler
 	private Mono<Void> resolveAsyncAttributes(Map<String, Object> model) {
 
 		List<String> names = new ArrayList<>();
-		List<Mono<Object>> valueMonos = new ArrayList<>();
+		List<Mono<?>> valueMonos = new ArrayList<>();
 
 		for (Map.Entry<String, ?> entry : model.entrySet()) {
 			ReactiveAdapter adapter = getAdapterRegistry().getAdapterFrom(null, entry.getValue());
 			if (adapter != null) {
 				names.add(entry.getKey());
-				valueMonos.add(adapter.toMono(entry.getValue()).defaultIfEmpty(NO_VALUE));
+				if (adapter.getDescriptor().isMultiValue()) {
+					Flux<Object> value = adapter.toFlux(entry.getValue());
+					valueMonos.add(value.collectList().defaultIfEmpty(Collections.emptyList()));
+				}
+				else {
+					Mono<Object> value = adapter.toMono(entry.getValue());
+					valueMonos.add(value.defaultIfEmpty(NO_VALUE));
+				}
 			}
 		}
 

spring-web-reactive/src/test/java/org/springframework/web/reactive/result/view/ViewResolutionResultHandlerTests.java

@@ -33,6 +33,7 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 import rx.Completable;
+import rx.Observable;
 import rx.Single;
 
 import org.springframework.core.MethodParameter;
@@ -270,9 +271,11 @@ public class ViewResolutionResultHandlerTests {
 	@Test
 	public void modelWithAsyncAttributes() throws Exception {
 		this.bindingContext.getModel()
-				.addAttribute("bean1", Mono.just(new TestBean("Bean1")))
-				.addAttribute("bean2", Single.just(new TestBean("Bean2")))
-				.addAttribute("empty", Mono.empty());
+				.addAttribute("attr1", Mono.just(new TestBean("Bean1")))
+				.addAttribute("attr2", Flux.just(new TestBean("Bean1"), new TestBean("Bean2")))
+				.addAttribute("attr3", Single.just(new TestBean("Bean2")))
+				.addAttribute("attr4", Observable.just(new TestBean("Bean1"), new TestBean("Bean2")))
+				.addAttribute("attr5", Mono.empty());
 
 		ResolvableType type = forClass(void.class);
 		HandlerResult result = new HandlerResult(new Object(), null, returnType(type), this.bindingContext);
@@ -281,11 +284,13 @@ public class ViewResolutionResultHandlerTests {
 		this.request.setUri("/account");
 		handler.handleResult(this.exchange, result).blockMillis(5000);
 		assertResponseBody("account: {" +
-				"bean1=TestBean[name=Bean1], " +
-				"bean2=TestBean[name=Bean2], " +
-				"org.springframework.validation.BindingResult.bean1=" +
+				"attr1=TestBean[name=Bean1], " +
+				"attr2=[TestBean[name=Bean1], TestBean[name=Bean2]], " +
+				"attr3=TestBean[name=Bean2], " +
+				"attr4=[TestBean[name=Bean1], TestBean[name=Bean2]], " +
+				"org.springframework.validation.BindingResult.attr1=" +
 				"org.springframework.validation.BeanPropertyBindingResult: 0 errors, " +
-				"org.springframework.validation.BindingResult.bean2=" +
+				"org.springframework.validation.BindingResult.attr3=" +
 				"org.springframework.validation.BeanPropertyBindingResult: 0 errors" +
 				"}");
 	}