Updates to WebFlux fragment rendering API

See gh-33162

Author: rstoyanchev

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

@@ -0,0 +1,139 @@
+/*
+ * 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.reactive.result.view;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Map;
+import java.util.function.Consumer;
+
+import org.reactivestreams.Publisher;
+import reactor.core.publisher.Flux;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.lang.Nullable;
+
+/**
+ * Default implementation of {@link FragmentsRendering.Builder}.
+ *
+ * @author Rossen Stoyanchev
+ * @since 6.2
+ */
+class DefaultFragmentsRenderingBuilder implements FragmentsRendering.Builder {
+
+	@Nullable
+	private Collection<Fragment> fragmentsCollection;
+
+	@Nullable
+	private final Flux<Fragment> fragmentsFlux;
+
+	@Nullable
+	private HttpStatusCode status;
+
+	@Nullable
+	private HttpHeaders headers;
+
+	DefaultFragmentsRenderingBuilder(Collection<Fragment> fragments) {
+		this.fragmentsCollection = new ArrayList<>(fragments);
+		this.fragmentsFlux = null;
+	}
+
+	DefaultFragmentsRenderingBuilder(Publisher<Fragment> fragments) {
+		this.fragmentsFlux = Flux.from(fragments);
+	}
+
+
+	@Override
+	public FragmentsRendering.Builder status(HttpStatusCode status) {
+		this.status = status;
+		return this;
+	}
+
+	@Override
+	public FragmentsRendering.Builder header(String headerName, String... headerValues) {
+		initHeaders().put(headerName, Arrays.asList(headerValues));
+		return this;
+	}
+
+	@Override
+	public FragmentsRendering.Builder headers(Consumer<HttpHeaders> headersConsumer) {
+		headersConsumer.accept(initHeaders());
+		return this;
+	}
+
+	private HttpHeaders initHeaders() {
+		if (this.headers == null) {
+			this.headers = new HttpHeaders();
+		}
+		return this.headers;
+	}
+
+	@Override
+	public FragmentsRendering.Builder fragment(String viewName, Map<String, Object> model) {
+		return fragment(Fragment.create(viewName, model));
+	}
+
+	@Override
+	public FragmentsRendering.Builder fragment(String viewName) {
+		return fragment(Fragment.create(viewName));
+	}
+
+	@Override
+	public FragmentsRendering.Builder fragment(Fragment fragment) {
+		initFragmentsCollection().add(fragment);
+		return this;
+	}
+
+	private Collection<Fragment> initFragmentsCollection() {
+		if (this.fragmentsCollection == null) {
+			this.fragmentsCollection = new ArrayList<>();
+		}
+		return this.fragmentsCollection;
+	}
+
+	@Override
+	public FragmentsRendering build() {
+		return new DefaultFragmentsRendering(
+				this.status, (this.headers != null ? this.headers : HttpHeaders.EMPTY), getFragmentsFlux());
+	}
+
+	private Flux<Fragment> getFragmentsFlux() {
+		if (this.fragmentsFlux != null && this.fragmentsCollection != null) {
+			return this.fragmentsFlux.concatWith(Flux.fromIterable(this.fragmentsCollection));
+		}
+		else if (this.fragmentsFlux != null) {
+			return this.fragmentsFlux;
+		}
+		else if (this.fragmentsCollection != null) {
+			return Flux.fromIterable(this.fragmentsCollection);
+		}
+		else {
+			return Flux.empty();
+		}
+	}
+
+
+	/**
+	 * Default implementation of {@link FragmentsRendering}.
+	 */
+	private record DefaultFragmentsRendering(@Nullable HttpStatusCode status, HttpHeaders headers, Flux<Fragment> fragments)
+			implements FragmentsRendering {
+	}
+
+}

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

@@ -16,19 +16,23 @@
 
 package org.springframework.web.reactive.result.view;
 
+import java.util.Collections;
+import java.util.LinkedHashMap;
 import java.util.Map;
 
 import org.springframework.lang.Nullable;
+import org.springframework.ui.Model;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 
 /**
- * Container for a model and a view for use with {@link FragmentRendering} and
+ * Container for a model and a view for use with {@link FragmentsRendering} and
  * multi-view rendering. For full page rendering with a single model and view,
  * use {@link Rendering}.
  *
  * @author Rossen Stoyanchev
  * @since 6.2
- * @see FragmentRendering
+ * @see FragmentsRendering
  */
 public final class Fragment {
 
@@ -38,10 +42,11 @@ public final class Fragment {
 	@Nullable
 	private final View view;
 
-	private final Map<String, Object> model;
+	@Nullable
+	private Map<String, Object> model;
 
 
-	private Fragment(@Nullable String viewName, @Nullable View view, Map<String, Object> model) {
+	private Fragment(@Nullable String viewName, @Nullable View view, @Nullable Map<String, Object> model) {
 		this.viewName = viewName;
 		this.view = view;
 		this.model = model;
@@ -73,15 +78,29 @@ public View view() {
 	}
 
 	/**
-	 * Return the model for this Fragment.
+	 * Return the model for this Fragment, or an empty map.
 	 */
 	public Map<String, Object> model() {
-		return this.model;
+		return (this.model != null ? this.model : Collections.emptyMap());
+	}
+
+	/**
+	 * Merge attributes from the request model if not already present.
+	 */
+	public void mergeAttributes(Model model) {
+		if (CollectionUtils.isEmpty(model.asMap())) {
+			return;
+		}
+		if (this.model == null) {
+			this.model = new LinkedHashMap<>();
+		}
+		model.asMap().forEach((key, value) -> this.model.putIfAbsent(key, value));
 	}
 
+
 	@Override
 	public String toString() {
-		return "Fragment [view=" + formatView() + "; model=" + this.model + "]";
+		return "Fragment [view=" + formatView() + "; model=" + model() + "]";
 	}
 
 	private String formatView() {
@@ -90,14 +109,23 @@ private String formatView() {
 
 
 	/**
-	 * Create a Fragment with a view name and a model.
+	 * Create a Fragment with a view name and a model, also inheriting model
+	 * attributes from the top-level model for the request.
 	 */
 	public static Fragment create(String viewName, Map<String, Object> model) {
 		return new Fragment(viewName, null, model);
 	}
 
 	/**
-	 * Create a Fragment with a resolved {@link View} instance and a model.
+	 * Create a Fragment with a view name only, inheriting model attributes from
+	 * the top-level model for the request.
+	 */
+	public static Fragment create(String viewName) {
+		return new Fragment(viewName, null, null);
+	}
+
+	/**
+	 * Variant of {@link #create(String, Map)} with a resolved {@link View}.
 	 */
 	public static Fragment create(View view, Map<String, Object> model) {
 		return new Fragment(null, view, model);