Resolve async model attributes in AbstractView

This change allows the functional WebFlux API to support natively
reactive types and also makes it possible for View implementations to
disable async attributes resolution if they want for example take
advantage of stream rendering.

It also makes AbstractView#getModelAttributes() asynchronous.

Issue: SPR-15368

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

@@ -18,13 +18,13 @@ package org.springframework.web.reactive.result.view;
 
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
-import java.util.ArrayList;
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.springframework.core.ReactiveAdapter;
+import org.springframework.core.ReactiveAdapterRegistry;
+import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.springframework.context.ApplicationContext;
@@ -48,9 +48,13 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 	/** Logger that is available to subclasses */
 	protected final Log logger = LogFactory.getLog(getClass());
 
+	private static final Object NO_VALUE = new Object();
+
 
 	private final List<MediaType> mediaTypes = new ArrayList<>(4);
 
+	private final ReactiveAdapterRegistry adapterRegistry;
+
 	private Charset defaultCharset = StandardCharsets.UTF_8;
 
 	private String requestContextAttribute;
@@ -59,7 +63,12 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 
 
 	public AbstractView() {
+		this(new ReactiveAdapterRegistry());
+	}
+
+	public AbstractView(ReactiveAdapterRegistry registry) {
 		this.mediaTypes.add(ViewResolverSupport.DEFAULT_CONTENT_TYPE);
+		this.adapterRegistry = registry;
 	}
 
 
@@ -146,14 +155,13 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 			exchange.getResponse().getHeaders().setContentType(contentType);
 		}
 
-		Map<String, Object> mergedModel = getModelAttributes(model, exchange);
-
-		// Expose RequestContext?
-		if (this.requestContextAttribute != null) {
-			mergedModel.put(this.requestContextAttribute, createRequestContext(exchange, mergedModel));
-		}
-
-		return renderInternal(mergedModel, contentType, exchange);
+		return getModelAttributes(model, exchange).then(mergedModel -> {
+			// Expose RequestContext?
+			if (this.requestContextAttribute != null) {
+				mergedModel.put(this.requestContextAttribute, createRequestContext(exchange, mergedModel));
+			}
+			return renderInternal(mergedModel, contentType, exchange);
+		});
 	}
 
 	/**
@@ -161,7 +169,7 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 	 * <p>The default implementation creates a combined output Map that includes
 	 * model as well as static attributes with the former taking precedence.
 	 */
-	protected Map<String, Object> getModelAttributes(Map<String, ?> model, ServerWebExchange exchange) {
+	protected Mono<Map<String, Object>> getModelAttributes(Map<String, ?> model, ServerWebExchange exchange) {
 		int size = (model != null ? model.size() : 0);
 
 		Map<String, Object> attributes = new LinkedHashMap<>(size);
@@ -169,7 +177,55 @@ public abstract class AbstractView implements View, ApplicationContextAware {
 			attributes.putAll(model);
 		}
 
-		return attributes;
+		return resolveAsyncAttributes(attributes).then(Mono.just(attributes));
+	}
+
+	/**
+	 * By default, resolve async attributes supported by the {@link ReactiveAdapterRegistry} to their blocking counterparts.
+	 * <p>View implementations capable of taking advantage of reactive types can override this method if needed.
+	 * @return {@code Mono} to represent when the async attributes have been resolved
+	 */
+	protected Mono<Void> resolveAsyncAttributes(Map<String, Object> model) {
+
+		List<String> names = new ArrayList<>();
+		List<Mono<?>> valueMonos = new ArrayList<>();
+
+		for (Map.Entry<String, ?> entry : model.entrySet()) {
+			Object value =  entry.getValue();
+			if (value == null) {
+				continue;
+			}
+			ReactiveAdapter adapter = this.adapterRegistry.getAdapter(null, value);
+			if (adapter != null) {
+				names.add(entry.getKey());
+				if (adapter.isMultiValue()) {
+					Flux<Object> fluxValue = Flux.from(adapter.toPublisher(value));
+					valueMonos.add(fluxValue.collectList().defaultIfEmpty(Collections.emptyList()));
+				}
+				else {
+					Mono<Object> monoValue = Mono.from(adapter.toPublisher(value));
+					valueMonos.add(monoValue.defaultIfEmpty(NO_VALUE));
+				}
+			}
+		}
+
+		if (names.isEmpty()) {
+			return Mono.empty();
+		}
+
+		return Mono.when(valueMonos,
+				values -> {
+					for (int i=0; i < values.length; i++) {
+						if (values[i] != NO_VALUE) {
+							model.put(names.get(i), values[i]);
+						}
+						else {
+							model.remove(names.get(i));
+						}
+					}
+					return NO_VALUE;
+				})
+				.then();
 	}
 
 	/**

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

@@ -224,10 +224,9 @@ public class ViewResolutionResultHandler extends HandlerResultHandlerSupport
 						viewsMono = resolveViews(getDefaultViewName(exchange), locale);
 					}
 
-					return resolveAsyncAttributes(model.asMap())
-							.doOnSuccess(aVoid -> addBindingResult(result.getBindingContext(), exchange))
-							.then(viewsMono)
-							.then(views -> render(views, model.asMap(), exchange));
+					addBindingResult(result.getBindingContext(), exchange);
+
+					return viewsMono.then(views -> render(views, model.asMap(), exchange));
 				});
 	}
 
@@ -274,44 +273,7 @@ public class ViewResolutionResultHandler extends HandlerResultHandlerSupport
 		return ClassUtils.getShortNameAsProperty(returnValueType);
 	}
 
-	private Mono<Void> resolveAsyncAttributes(Map<String, Object> model) {
-
-		List<String> names = new ArrayList<>();
-		List<Mono<?>> valueMonos = new ArrayList<>();
 
-		for (Map.Entry<String, ?> entry : model.entrySet()) {
-			ReactiveAdapter adapter = getAdapterRegistry().getAdapter(null, entry.getValue());
-			if (adapter != null) {
-				names.add(entry.getKey());
-				if (adapter.isMultiValue()) {
-					Flux<Object> value = Flux.from(adapter.toPublisher(entry.getValue()));
-					valueMonos.add(value.collectList().defaultIfEmpty(Collections.emptyList()));
-				}
-				else {
-					Mono<Object> value = Mono.from(adapter.toPublisher(entry.getValue()));
-					valueMonos.add(value.defaultIfEmpty(NO_VALUE));
-				}
-			}
-		}
-
-		if (names.isEmpty()) {
-			return Mono.empty();
-		}
-
-		return Mono.when(valueMonos,
-				values -> {
-					for (int i=0; i < values.length; i++) {
-						if (values[i] != NO_VALUE) {
-							model.put(names.get(i), values[i]);
-						}
-						else {
-							model.remove(names.get(i));
-						}
-					}
-					return NO_VALUE;
-				})
-				.then();
-	}
 
 	private void addBindingResult(BindingContext context, ServerWebExchange exchange) {
 		Map<String, Object> model = context.getModel().asMap();

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

@@ -0,0 +1,77 @@
+package org.springframework.web.reactive.result.view;
+
+import io.reactivex.Observable;
+import io.reactivex.Single;
+import org.junit.Before;
+import org.junit.Test;
+import org.springframework.http.MediaType;
+import org.springframework.mock.http.server.reactive.test.MockServerHttpRequest;
+import org.springframework.mock.http.server.reactive.test.MockServerWebExchange;
+import org.springframework.tests.sample.beans.TestBean;
+import org.springframework.ui.Model;
+import org.springframework.web.server.ServerWebExchange;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.logging.Level;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+/**
+ * Unit tests for {@link AbstractView}.
+ *
+ * @author Sebastien Deleuze
+ */
+public class AbstractViewTests {
+
+    private MockServerWebExchange exchange;
+
+    @Before
+    public void setup() {
+        this.exchange = MockServerHttpRequest.get("/").toExchange();
+    }
+
+    @Test
+    public void resolveAsyncAttributes() {
+
+        TestBean testBean1 = new TestBean("Bean1");
+        TestBean testBean2 = new TestBean("Bean2");
+        Map<String, Object> attributes = new HashMap();
+        attributes.put("attr1", Mono.just(testBean1));
+        attributes.put("attr2", Flux.just(testBean1, testBean2));
+        attributes.put("attr3", Single.just(testBean2));
+        attributes.put("attr4", Observable.just(testBean1, testBean2));
+        attributes.put("attr5", Mono.empty());
+
+        TestView view = new TestView();
+        StepVerifier.create(view.render(attributes, null, this.exchange)).verifyComplete();
+
+        assertEquals(testBean1, view.attributes.get("attr1"));
+        assertArrayEquals(new TestBean[] {testBean1, testBean2}, ((List<TestBean>)view.attributes.get("attr2")).toArray());
+        assertEquals(testBean2, view.attributes.get("attr3"));
+        assertArrayEquals(new TestBean[] {testBean1, testBean2}, ((List<TestBean>)view.attributes.get("attr4")).toArray());
+        assertNull(view.attributes.get("attr5"));
+    }
+
+
+    private static class TestView extends AbstractView {
+
+        private Map<String, Object> attributes;
+
+        @Override
+        protected Mono<Void> renderInternal(Map<String, Object> renderAttributes, MediaType contentType, ServerWebExchange exchange) {
+            this.attributes = renderAttributes;
+            return Mono.empty();
+        }
+
+        public Map<String, Object> getAttributes() {
+            return this.attributes;
+        }
+    }
+}

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

@@ -61,7 +61,7 @@ public class RedirectViewTests {
 	public void defaultStatusCode() {
 		String url = "http://url.somewhere.com";
 		RedirectView view = new RedirectView(url);
-		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange);
+		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange).block();
 		assertEquals(HttpStatus.SEE_OTHER, this.exchange.getResponse().getStatusCode());
 		assertEquals(URI.create(url), this.exchange.getResponse().getHeaders().getLocation());
 	}
@@ -70,7 +70,7 @@ public class RedirectViewTests {
 	public void customStatusCode() {
 		String url = "http://url.somewhere.com";
 		RedirectView view = new RedirectView(url, HttpStatus.FOUND);
-		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange);
+		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange).block();
 		assertEquals(HttpStatus.FOUND, this.exchange.getResponse().getStatusCode());
 		assertEquals(URI.create(url), this.exchange.getResponse().getHeaders().getLocation());
 	}
@@ -79,7 +79,7 @@ public class RedirectViewTests {
 	public void contextRelative() {
 		String url = "/test.html";
 		RedirectView view = new RedirectView(url);
-		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange);
+		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange).block();
 		assertEquals(URI.create("/context/test.html"), this.exchange.getResponse().getHeaders().getLocation());
 	}
 
@@ -87,7 +87,7 @@ public class RedirectViewTests {
 	public void contextRelativeQueryParam() {
 		String url = "/test.html?id=1";
 		RedirectView view = new RedirectView(url);
-		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange);
+		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange).block();
 		assertEquals(URI.create("/context/test.html?id=1"), this.exchange.getResponse().getHeaders().getLocation());
 	}
 
@@ -111,7 +111,7 @@ public class RedirectViewTests {
 		String url = "http://url.somewhere.com?foo={foo}";
 		Map<String, String> model = Collections.singletonMap("foo", "bar");
 		RedirectView view = new RedirectView(url);
-		view.render(model, MediaType.TEXT_HTML, this.exchange);
+		view.render(model, MediaType.TEXT_HTML, this.exchange).block();
 		assertEquals(URI.create("http://url.somewhere.com?foo=bar"), this.exchange.getResponse().getHeaders().getLocation());
 	}
 
@@ -121,7 +121,7 @@ public class RedirectViewTests {
 		Map<String, String> attributes = Collections.singletonMap("foo", "bar");
 		this.exchange.getAttributes().put(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, attributes);
 		RedirectView view = new RedirectView(url);
-		view.render(new HashMap<>(), MediaType.TEXT_HTML, exchange);
+		view.render(new HashMap<>(), MediaType.TEXT_HTML, exchange).block();
 		assertEquals(URI.create("http://url.somewhere.com?foo=bar"), this.exchange.getResponse().getHeaders().getLocation());
 	}
 
@@ -130,7 +130,7 @@ public class RedirectViewTests {
 		RedirectView view = new RedirectView("http://url.somewhere.com?foo=bar#bazz");
 		view.setPropagateQuery(true);
 		this.exchange = MockServerHttpRequest.get("http://url.somewhere.com?a=b&c=d").toExchange();
-		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange);
+		view.render(new HashMap<>(), MediaType.TEXT_HTML, this.exchange).block();
 		assertEquals(HttpStatus.SEE_OTHER, this.exchange.getResponse().getStatusCode());
 		assertEquals(URI.create("http://url.somewhere.com?foo=bar&a=b&c=d#bazz"),
 				this.exchange.getResponse().getHeaders().getLocation());

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

@@ -32,7 +32,6 @@ 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;
@@ -249,34 +248,6 @@ public class ViewResolutionResultHandlerTests {
 				.verify();
 	}
 
-	@Test
-	public void modelWithAsyncAttributes() throws Exception {
-		this.bindingContext.getModel()
-				.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());
-
-		MethodParameter returnType = on(TestController.class).resolveReturnType(void.class);
-		HandlerResult result = new HandlerResult(new Object(), null, returnType, this.bindingContext);
-		ViewResolutionResultHandler handler = resultHandler(new TestViewResolver("account"));
-
-		MockServerWebExchange exchange = get("/account").toExchange();
-
-		handler.handleResult(exchange, result).block(Duration.ofMillis(5000));
-		assertResponseBody(exchange, "account: {" +
-				"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.attr3=" +
-				"org.springframework.validation.BeanPropertyBindingResult: 0 errors" +
-				"}");
-	}
-
 
 	private ViewResolutionResultHandler resultHandler(ViewResolver... resolvers) {
 		return resultHandler(Collections.emptyList(), resolvers);