Updates to WebMVC fragment rendering API

See gh-33162

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

@@ -27,7 +27,7 @@ import org.springframework.web.method.support.ModelAndViewContainer;
 import org.springframework.web.servlet.ModelAndView;
 import org.springframework.web.servlet.SmartView;
 import org.springframework.web.servlet.View;
-import org.springframework.web.servlet.view.FragmentsView;
+import org.springframework.web.servlet.view.FragmentsRendering;
 
 /**
  * Handles return values of type {@link ModelAndView} copying view and model
@@ -78,7 +78,7 @@ public class ModelAndViewMethodReturnValueHandler implements HandlerMethodReturn
 		if (Collection.class.isAssignableFrom(type)) {
 			type = returnType.nested().getNestedParameterType();
 		}
-		return ModelAndView.class.isAssignableFrom(type);
+		return (ModelAndView.class.isAssignableFrom(type) || FragmentsRendering.class.isAssignableFrom(type));
 	}
 
 	@SuppressWarnings("unchecked")
@@ -92,7 +92,11 @@ public class ModelAndViewMethodReturnValueHandler implements HandlerMethodReturn
 		}
 
 		if (returnValue instanceof Collection<?> mavs) {
-			mavContainer.setView(FragmentsView.create((Collection<ModelAndView>) mavs));
+			returnValue = FragmentsRendering.with((Collection<ModelAndView>) mavs).build();
+		}
+
+		if (returnValue instanceof FragmentsRendering rendering) {
+			mavContainer.setView(rendering);
 			return;
 		}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/view/DefaultFragmentsRendering.java

@@ -17,6 +17,7 @@
 package org.springframework.web.servlet.view;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Locale;
 import java.util.Map;
@@ -31,27 +32,23 @@ import jakarta.servlet.http.HttpServletResponseWrapper;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.web.servlet.ModelAndView;
-import org.springframework.web.servlet.SmartView;
 import org.springframework.web.servlet.View;
 import org.springframework.web.servlet.ViewResolver;
 
 /**
- * {@link View} that enables rendering of a collection of fragments, each with
- * its own view and model, also inheriting common attributes from the top-level model.
+ * Default implementation of {@link FragmentsRendering} that can render fragments
+ * through the {@link org.springframework.web.servlet.SmartView} contract.
  *
  * @author Rossen Stoyanchev
  * @since 6.2
  */
-public class FragmentsView implements SmartView {
+final class DefaultFragmentsRendering implements FragmentsRendering {
 
 	private final Collection<ModelAndView> modelAndViews;
 
 
-	/**
-	 * Protected constructor to allow extension.
-	 */
-	protected FragmentsView(Collection<ModelAndView> modelAndViews) {
-		this.modelAndViews = modelAndViews;
+	DefaultFragmentsRendering(Collection<ModelAndView> modelAndViews) {
+		this.modelAndViews = new ArrayList<>(modelAndViews);
 	}
 
 
@@ -95,20 +92,9 @@ public class FragmentsView implements SmartView {
 		}
 	}
 
-
 	@Override
 	public String toString() {
-		return "FragmentsView " + this.modelAndViews;
-	}
-
-
-	/**
-	 * Factory method to create an instance with the given fragments.
-	 * @param modelAndViews the {@link ModelAndView} to use
-	 * @return the created {@code FragmentsView} instance
-	 */
-	public static FragmentsView create(Collection<ModelAndView> modelAndViews) {
-		return new FragmentsView(modelAndViews);
+		return "DefaultFragmentsRendering " + this.modelAndViews;
 	}
 
 

spring-webmvc/src/main/java/org/springframework/web/servlet/view/DefaultFragmentsRenderingBuilder.java

@@ -0,0 +1,64 @@
+/*
+ * 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.view;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Map;
+
+import org.springframework.web.servlet.ModelAndView;
+
+/**
+ * Default {@link FragmentsRendering.Builder} implementation that collects the
+ * fragments and creates a {@link DefaultFragmentsRendering}.
+ *
+ * @author Rossen Stoyanchev
+ * @since 6.2
+ */
+final class DefaultFragmentsRenderingBuilder implements FragmentsRendering.Builder {
+
+	private final Collection<ModelAndView> fragments = new ArrayList<>();
+
+
+	@Override
+	public DefaultFragmentsRenderingBuilder fragment(String viewName, Map<String, Object> model) {
+		return fragment(new ModelAndView(viewName, model));
+	}
+
+	@Override
+	public DefaultFragmentsRenderingBuilder fragment(String viewName) {
+		return fragment(new ModelAndView(viewName));
+	}
+
+	@Override
+	public DefaultFragmentsRenderingBuilder fragment(ModelAndView fragment) {
+		this.fragments.add(fragment);
+		return this;
+	}
+
+	@Override
+	public DefaultFragmentsRenderingBuilder fragments(Collection<ModelAndView> fragments) {
+		this.fragments.addAll(fragments);
+		return this;
+	}
+
+	@Override
+	public FragmentsRendering build() {
+		return new DefaultFragmentsRendering(this.fragments);
+	}
+
+}

spring-webmvc/src/main/java/org/springframework/web/servlet/view/FragmentsRendering.java

@@ -0,0 +1,116 @@
+/*
+ * 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.view;
+
+import java.util.Collection;
+import java.util.Map;
+
+import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.servlet.SmartView;
+
+/**
+ * Public API for HTML rendering a collection fragments each with its own view
+ * and model. For use with view technologies such as
+ * <a href="https://htmx.org/">htmx</a> where multiple page fragments may be
+ * rendered in a single response. Supported as a return value from a Spring MVC
+ * controller method.
+ *
+ * @author Rossen Stoyanchev
+ * @since 6.2
+ */
+public interface FragmentsRendering extends SmartView {
+
+
+	/**
+	 * Create a builder for {@link FragmentsRendering}, adding a fragment with
+	 * the given view name and model.
+	 * @param viewName the name of the view for the fragment
+	 * @param model attributes for the fragment in addition to model
+	 * attributes inherited from the shared model for the request
+	 * @return the created builder
+	 */
+	static Builder with(String viewName, Map<String, Object> model) {
+		return new DefaultFragmentsRenderingBuilder().fragment(viewName, model);
+	}
+
+	/**
+	 * Variant of {@link #with(String, Map)} with a view name only, but also
+	 * inheriting model attributes from the shared model for the request.
+	 * @param viewName the name of the view for the fragment
+	 * @return the created builder
+	 */
+	static Builder with(String viewName) {
+		return new DefaultFragmentsRenderingBuilder().fragment(viewName);
+	}
+
+	/**
+	 * Variant of {@link #with(String, Map)} with a collection of fragments.
+	 * @param fragments the fragments to add; each fragment also inherits model
+	 * attributes from the shared model for the request
+	 * @return the created builder
+	 */
+	static Builder with(Collection<ModelAndView> fragments) {
+		return new DefaultFragmentsRenderingBuilder().fragments(fragments);
+	}
+
+
+	/**
+	 * Defines a builder for {@link FragmentsRendering}.
+	 */
+	interface Builder {
+
+		/**
+		 * Add a fragment with a view name and a model.
+		 * @param viewName the name of the view for the fragment
+		 * @param model attributes for the fragment in addition to model
+		 * attributes inherited from the shared model for the request
+		 * @return this builder
+		 */
+		Builder fragment(String viewName, Map<String, Object> model);
+
+		/**
+		 * Add a fragment with a view name only, inheriting model attributes from
+		 * the model for the request.
+		 * @param viewName the name of the view for the fragment
+		 * @return this builder
+		 */
+		Builder fragment(String viewName);
+
+		/**
+		 * Add a fragment.
+		 * @param fragment the fragment to add; the fragment also inherits model
+		 * attributes from the shared model for the request
+		 * @return this builder
+		 */
+		Builder fragment(ModelAndView fragment);
+
+		/**
+		 * Add a collection of fragments.
+		 * @param fragments the fragments to add; each fragment also inherits model
+		 * attributes from the shared model for the request
+		 * @return this builder
+		 */
+		Builder fragments(Collection<ModelAndView> fragments);
+
+		/**
+		 * Build a {@link FragmentsRendering} instance.
+		 */
+		FragmentsRendering build();
+
+	}
+
+}

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

@@ -17,6 +17,8 @@
 package org.springframework.web.servlet.mvc.method.annotation;
 
 import java.lang.reflect.Method;
+import java.util.Collection;
+import java.util.List;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -26,7 +28,9 @@ import org.springframework.ui.ModelMap;
 import org.springframework.web.context.request.ServletWebRequest;
 import org.springframework.web.method.support.ModelAndViewContainer;
 import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.servlet.SmartView;
 import org.springframework.web.servlet.mvc.support.RedirectAttributesModelMap;
+import org.springframework.web.servlet.view.FragmentsRendering;
 import org.springframework.web.servlet.view.RedirectView;
 import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
 
@@ -60,6 +64,9 @@ class ModelAndViewMethodReturnValueHandlerTests {
 	@Test
 	void supportsReturnType() throws Exception {
 		assertThat(handler.supportsReturnType(returnParamModelAndView)).isTrue();
+		assertThat(handler.supportsReturnType(getReturnValueParam("fragmentsRendering"))).isTrue();
+		assertThat(handler.supportsReturnType(getReturnValueParam("fragmentsCollection"))).isTrue();
+
 		assertThat(handler.supportsReturnType(getReturnValueParam("viewName"))).isFalse();
 	}
 
@@ -81,6 +88,22 @@ class ModelAndViewMethodReturnValueHandlerTests {
 		assertThat(mavContainer.getModel().get("attrName")).isEqualTo("attrValue");
 	}
 
+	@Test
+	void handleFragmentsRendering() throws Exception {
+		FragmentsRendering rendering = FragmentsRendering.with("viewName").build();
+
+		handler.handleReturnValue(rendering, returnParamModelAndView, mavContainer, webRequest);
+		assertThat(mavContainer.getView()).isInstanceOf(SmartView.class);
+	}
+
+	@Test
+	void handleFragmentsCollection() throws Exception {
+		Collection<ModelAndView> fragments = List.of(new ModelAndView("viewName"));
+
+		handler.handleReturnValue(fragments, returnParamModelAndView, mavContainer, webRequest);
+		assertThat(mavContainer.getView()).isInstanceOf(SmartView.class);
+	}
+
 	@Test
 	void handleNull() throws Exception {
 		handler.handleReturnValue(null, returnParamModelAndView, mavContainer, webRequest);
@@ -173,4 +196,14 @@ class ModelAndViewMethodReturnValueHandlerTests {
 		return null;
 	}
 
+	@SuppressWarnings("unused")
+	FragmentsRendering fragmentsRendering() {
+		return null;
+	}
+
+	@SuppressWarnings("unused")
+	Collection<ModelAndView> fragmentsCollection() {
+		return null;
+	}
+
 }

spring-webmvc/src/test/java/org/springframework/web/servlet/view/DefaultFragmentsRenderingTests.java

@@ -38,12 +38,12 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.condition.JRE.JAVA_21;
 
 /**
- * Tests for rendering through {@link FragmentsView}.
+ * Tests for rendering through {@link DefaultFragmentsRendering}.
  *
  * @author Rossen Stoyanchev
  */
 @DisabledForJreRange(min = JAVA_21, disabledReason = "Kotlin doesn't support Java 21+ yet")
-public class FragmentsViewTests {
+public class DefaultFragmentsRenderingTests {
 
 
 	@Test
@@ -59,7 +59,7 @@ public class FragmentsViewTests {
 		MockHttpServletRequest request = new MockHttpServletRequest();
 		MockHttpServletResponse response = new MockHttpServletResponse();
 
-		FragmentsView view = FragmentsView.create(List.of(
+		DefaultFragmentsRendering view = new DefaultFragmentsRendering(List.of(
 				new ModelAndView("fragment1", Map.of("foo", "Foo")),
 				new ModelAndView("fragment2", Map.of("bar", "Bar"))));