Avoid affecting serialization of custom Page implementations in legacy mode.

Registering a StdConverter with Jackson to log a warning  about the Page serialization mode causes the target serializer to be only built for Page losing additional properties defined on extensions. We now instead register a no-op BeanSerializerModifier that issues the warning and doesn't affect the serializer selection.

Fixes GH-3137.

src/main/java/org/springframework/data/web/config/SpringDataJacksonConfiguration.java

@@ -15,6 +15,8 @@
  */
 package org.springframework.data.web.config;
 
+import java.util.List;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -27,8 +29,12 @@ import org.springframework.data.web.config.EnableSpringDataWebSupport.PageSerial
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 
+import com.fasterxml.jackson.databind.BeanDescription;
+import com.fasterxml.jackson.databind.SerializationConfig;
 import com.fasterxml.jackson.databind.annotation.JsonSerialize;
 import com.fasterxml.jackson.databind.module.SimpleModule;
+import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;
+import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
 import com.fasterxml.jackson.databind.ser.std.ToStringSerializerBase;
 import com.fasterxml.jackson.databind.util.StdConverter;
 
@@ -83,7 +89,8 @@ public class SpringDataJacksonConfiguration implements SpringDataJacksonModules
 			addSerializer(UNPAGED_TYPE, new UnpagedAsInstanceSerializer());
 
 			if (settings == null || settings.pageSerializationMode() == PageSerializationMode.DIRECT) {
-				setMixInAnnotation(PageImpl.class, WarningMixing.class);
+				setSerializerModifier(new WarningLoggingModifier());
+
 			} else {
 				setMixInAnnotation(PageImpl.class, WrappingMixing.class);
 			}
@@ -109,14 +116,6 @@ public class SpringDataJacksonConfiguration implements SpringDataJacksonModules
 			}
 		}
 
-		/**
-		 * A mixin for PageImpl to register a converter issuing the serialization warning.
-		 *
-		 * @author Oliver Drotbohm
-		 */
-		@JsonSerialize(converter = PlainPageSerializationWarning.class)
-		abstract class WarningMixing {}
-
 		@JsonSerialize(converter = PageModelConverter.class)
 		abstract class WrappingMixing {}
 
@@ -129,27 +128,35 @@ public class SpringDataJacksonConfiguration implements SpringDataJacksonModules
 			}
 		}
 
-		static class PlainPageSerializationWarning extends StdConverter<Page<?>, Page<?>> {
+		/**
+		 * A {@link BeanSerializerModifier} that logs a warning message if an instance of {@link Page} will be rendered.
+		 *
+		 * @author Oliver Drotbohm
+		 */
+		static class WarningLoggingModifier extends BeanSerializerModifier {
 
-			private static final Logger LOGGER = LoggerFactory.getLogger(PlainPageSerializationWarning.class);
+			private static final Logger LOGGER = LoggerFactory.getLogger(WarningLoggingModifier.class);
 			private static final String MESSAGE = """
 					Serializing PageImpl instances as-is is not supported, meaning that there is no guarantee about the stability of the resulting JSON structure!
 						For a stable JSON structure, please use Spring Data's PagedModel (globally via @EnableSpringDataWebSupport(pageSerializationMode = VIA_DTO))
 						or Spring HATEOAS and Spring Data's PagedResourcesAssembler as documented in https://docs.spring.io/spring-data/commons/reference/repositories/core-extensions.html#core.web.pageables.
 					""";
 
+			private static final long serialVersionUID = 954857444010009875L;
+
 			private boolean warningRendered = false;
 
-			@Nullable
 			@Override
-			public Page<?> convert(@Nullable Page<?> value) {
+			public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc,
+					List<BeanPropertyWriter> beanProperties) {
+
+				if (Page.class.isAssignableFrom(beanDesc.getBeanClass()) && !warningRendered) {
 
-				if (!warningRendered) {
 					this.warningRendered = true;
 					LOGGER.warn(MESSAGE);
 				}
 
-				return value;
+				return super.changeProperties(config, beanDesc, beanProperties);
 			}
 		}
 	}

src/test/java/org/springframework/data/web/PageImplJsonSerializationUnitTests.java

@@ -45,7 +45,16 @@ class PageImplJsonSerializationUnitTests {
 		assertJsonRendering(PageSerializationMode.VIA_DTO, "$.content", "$.page");
 	}
 
+	@Test // GH-3137
+	void serializesCustomPageAsPageImpl() {
+		assertJsonRendering(PageSerializationMode.DIRECT, new Extension<>("header"), "$.pageable", "$.last", "$.first");
+	}
+
 	private static void assertJsonRendering(PageSerializationMode mode, String... jsonPaths) {
+		assertJsonRendering(mode, new PageImpl<>(Collections.emptyList()), jsonPaths);
+	}
+
+	private static void assertJsonRendering(PageSerializationMode mode, PageImpl<?> page, String... jsonPaths) {
 
 		SpringDataWebSettings settings = new SpringDataWebSettings(mode);
 
@@ -54,11 +63,24 @@ class PageImplJsonSerializationUnitTests {
 
 		assertThatNoException().isThrownBy(() -> {
 
-			String result = mapper.writeValueAsString(new PageImpl<>(Collections.emptyList()));
+			String result = mapper.writeValueAsString(page);
 
 			for (String jsonPath : jsonPaths) {
 				assertThat(JsonPath.<Object> read(result, jsonPath)).isNotNull();
 			}
 		});
 	}
+
+	static class Extension<T> extends PageImpl<T> {
+
+		private Object header;
+
+		public Extension(Object header) {
+			super(Collections.emptyList());
+		}
+
+		public Object getHeader() {
+			return header;
+		}
+	}
 }

src/test/java/org/springframework/data/web/config/SpringDataJacksonConfigurationUnitTests.java

@@ -1,42 +0,0 @@
-/*
- * Copyright 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.data.web.config;
-
-import static org.assertj.core.api.Assertions.*;
-
-import org.junit.jupiter.api.Test;
-import org.springframework.data.domain.PageImpl;
-import org.springframework.data.web.config.SpringDataJacksonConfiguration.PageModule;
-import org.springframework.data.web.config.SpringDataJacksonConfiguration.PageModule.WarningMixing;
-
-import com.fasterxml.jackson.databind.ObjectMapper;
-
-/**
- * Unit tests for {@link SpringDataJacksonConfiguration}.
- *
- * @author Oliver Drotbohm
- */
-class SpringDataJacksonConfigurationUnitTests {
-
-	@Test // GH-3101
-	void usesDirectRenderingIfNoSpringDataWebSettingsArePresent() {
-
-		ObjectMapper mapper = new ObjectMapper();
-		mapper.registerModule(new PageModule(null));
-
-		assertThat(mapper.getSerializationConfig().findMixInClassFor(PageImpl.class)).isEqualTo(WarningMixing.class);
-	}
-}