Add support for Streamable wrappers.

We now support conversion to wrapper types implementing Streamable.

See #4070

Author: mp911de

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/aot/JpaCodeBlocks.java

@@ -29,6 +29,8 @@
 
 import org.springframework.core.MethodParameter;
 import org.springframework.core.annotation.MergedAnnotation;
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.dao.IncorrectResultSizeDataAccessException;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.Score;
@@ -707,6 +709,12 @@ public CodeBlock build() {
 
 					if (isStreamable(methodReturn)) {
 						builder.addStatement("return ($1T) $1T.of($2L)", Streamable.class, context.localVariable("resultList"));
+					} else if (isStreamableWrapper(methodReturn) && canConvert(Streamable.class, methodReturn)) {
+
+						builder.addStatement(
+								"return ($1T) $2T.getSharedInstance().convert($3T.of($4L), $5T.valueOf($3T.class), $5T.valueOf($1T.class))",
+								methodReturn.toClass(), DefaultConversionService.class, Streamable.class,
+								context.localVariable("resultList"), TypeDescriptor.class);
 					} else {
 						builder.addStatement("return ($T) $L", List.class, context.localVariable("resultList"));
 					}
@@ -775,10 +783,14 @@ public CodeBlock build() {
 				} else {
 
 					if (queryMethod.isCollectionQuery()) {
-
 						if (isStreamable(methodReturn)) {
 							builder.addStatement("return ($T) $T.of($L.getResultList())", methodReturn.getTypeName(),
 									Streamable.class, queryVariableName);
+						} else if (isStreamableWrapper(methodReturn) && canConvert(Streamable.class, methodReturn)) {
+							builder.addStatement(
+									"return ($1T) $2T.getSharedInstance().convert($3T.of($4L.getResultList()), $5T.valueOf($3T.class), $5T.valueOf($1T.class))",
+									methodReturn.toClass(), DefaultConversionService.class, Streamable.class, queryVariableName,
+									TypeDescriptor.class);
 						} else {
 							builder.addStatement("return ($T) $L.getResultList()", methodReturn.getTypeName(), queryVariableName);
 						}
@@ -811,10 +823,18 @@ public CodeBlock build() {
 			return builder.build();
 		}
 
+		private boolean canConvert(Class<?> from, MethodReturn methodReturn) {
+			return DefaultConversionService.getSharedInstance().canConvert(from, methodReturn.toClass());
+		}
+
 		private static boolean isStreamable(MethodReturn methodReturn) {
 			return methodReturn.toClass().equals(Streamable.class);
 		}
 
+		private static boolean isStreamableWrapper(MethodReturn methodReturn) {
+			return !isStreamable(methodReturn) && Streamable.class.isAssignableFrom(methodReturn.toClass());
+		}
+
 		public static boolean returnsModifying(Class<?> returnType) {
 
 			return returnType == int.class || returnType == long.class || returnType == Integer.class

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/UserRepositoryTests.java

@@ -74,6 +74,7 @@
 import org.springframework.data.jpa.repository.sample.SampleEvaluationContextExtension.SampleSecurityContextHolder;
 import org.springframework.data.jpa.repository.sample.UserRepository;
 import org.springframework.data.jpa.repository.sample.UserRepository.NameOnly;
+import org.springframework.data.jpa.repository.sample.Users;
 import org.springframework.data.jpa.util.DisabledOnHibernate;
 import org.springframework.data.util.Streamable;
 import org.springframework.test.context.ContextConfiguration;
@@ -2157,6 +2158,15 @@ void supportsStreamableForPageableMethod() {
 		assertThat(users).hasSize(2);
 	}
 
+	@Test // GH-4070
+	void supportsStreamableWrapper() {
+
+		flushTestUsers();
+
+		Users users = repository.readUsersByFirstnameNotNull(PageRequest.of(0, 2));
+		assertThat(users).hasSize(2);
+	}
+
 	@Test // DATAJPA-218
 	void findAllByExample() {
 

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/sample/UserRepository.java

@@ -536,6 +536,8 @@ List<User> findUsersByFirstnameForSpELExpressionWithParameterIndexOnlyWithEntity
 
 	Streamable<User> readStreamableAllByFirstnameNotNull(Pageable pageable);
 
+	Users readUsersByFirstnameNotNull(Pageable pageable);
+
 	// DATAJPA-830
 	List<User> findByLastnameNotContaining(String part);
 

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/sample/Users.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2025 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.jpa.repository.sample;
+
+import java.util.Iterator;
+
+import org.springframework.data.jpa.domain.sample.User;
+import org.springframework.data.util.Streamable;
+
+/**
+ * @author Mark Paluch
+ */
+public class Users implements Streamable<User> {
+
+	private final Streamable<User> users;
+
+	private Users(Streamable<User> users) {
+		this.users = users;
+	}
+
+	public static Users of(Streamable<User> users) {
+		return new Users(users);
+	}
+
+	@Override
+	public Iterator<User> iterator() {
+		return users.iterator();
+	}
+
+}