Introduce ManagedTypes.

We now provide an abstraction to describe a collection of entity types that can be provided to the mapping context as improvement over `Set<Class>` for easier context setup.

Original pull request: #2635.
Closes #2634.

src/main/java/org/springframework/data/domain/ManagedTypes.java

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2022 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.domain;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+import java.util.stream.Stream;
+
+import org.springframework.data.util.Lazy;
+
+/**
+ * Types managed by a Spring Data implementation. Used to predefine a set of know entities that might need processing
+ * during the Spring container, Spring Data Repository initialization phase.
+ *
+ * @author Christoph Strobl
+ * @author John Blum
+ * @see java.lang.FunctionalInterface
+ * @since 3.0
+ */
+@FunctionalInterface
+public interface ManagedTypes {
+
+	/**
+	 * Factory method used to construct a new instance of {@link ManagedTypes} containing no {@link Class types}.
+	 *
+	 * @return an empty {@link ManagedTypes} instance.
+	 * @see java.util.Collections#emptySet()
+	 * @see #fromIterable(Iterable)
+	 */
+	static ManagedTypes empty() {
+		return fromIterable(Collections.emptySet());
+	}
+
+	/**
+	 * Factory method used to construct {@link ManagedTypes} from the given, required {@link Iterable} of {@link Class
+	 * types}.
+	 *
+	 * @param types {@link Iterable} of {@link Class types} used to initialize the {@link ManagedTypes}; must not be
+	 *          {@literal null}.
+	 * @return new instance of {@link ManagedTypes} initialized the given, required {@link Iterable} of {@link Class
+	 *         types}.
+	 * @see java.lang.Iterable
+	 * @see #fromStream(Stream)
+	 * @see #fromSupplier(Supplier)
+	 */
+	static ManagedTypes fromIterable(Iterable<? extends Class<?>> types) {
+		return types::forEach;
+	}
+
+	/**
+	 * Factory method used to construct {@link ManagedTypes} from the given, required {@link Stream} of {@link Class
+	 * types}.
+	 *
+	 * @param types {@link Stream} of {@link Class types} used to initialize the {@link ManagedTypes}; must not be
+	 *          {@literal null}.
+	 * @return new instance of {@link ManagedTypes} initialized the given, required {@link Stream} of {@link Class types}.
+	 * @see java.util.stream.Stream
+	 * @see #fromIterable(Iterable)
+	 * @see #fromSupplier(Supplier)
+	 */
+	static ManagedTypes fromStream(Stream<? extends Class<?>> types) {
+		return types::forEach;
+	}
+
+	/**
+	 * Factory method used to construct {@link ManagedTypes} from the given, required {@link Supplier} of an
+	 * {@link Iterable} of {@link Class types}.
+	 *
+	 * @param dataProvider {@link Supplier} of an {@link Iterable} of {@link Class types} used to lazily initialize the
+	 *          {@link ManagedTypes}; must not be {@literal null}.
+	 * @return new instance of {@link ManagedTypes} initialized the given, required {@link Supplier} of an
+	 *         {@link Iterable} of {@link Class types}.
+	 * @see java.util.function.Supplier
+	 * @see java.lang.Iterable
+	 * @see #fromIterable(Iterable) 
+	 * @see #fromStream(Stream) 
+	 */
+	static ManagedTypes fromSupplier(Supplier<Iterable<Class<?>>> dataProvider) {
+
+		return new ManagedTypes() {
+
+			final Lazy<Iterable<Class<?>>> lazyProvider = Lazy.of(dataProvider);
+
+			@Override
+			public void forEach(Consumer<Class<?>> action) {
+				lazyProvider.get().forEach(action);
+			}
+		};
+	}
+
+	/**
+	 * Applies the given {@link Consumer action} to each of the {@link Class types} contained in this {@link ManagedTypes}
+	 * instance.
+	 *
+	 * @param action {@link Consumer} defining the action to perform on the {@link Class types} contained in this
+	 *          {@link ManagedTypes} instance; must not be {@literal null}.
+	 * @see java.util.function.Consumer
+	 */
+	void forEach(Consumer<Class<?>> action);
+
+	/**
+	 * Returns all the {@link ManagedTypes} in a {@link List}.
+	 *
+	 * @return these {@link ManagedTypes} in a {@link List}; never {@literal null}.
+	 * @see java.util.List
+	 */
+	default List<Class<?>> toList() {
+
+		List<Class<?>> list = new ArrayList<>(100);
+		forEach(list::add);
+		return list;
+	}
+}