Add MockSpringFactoriesLoader

Add a `MockSpringFactoriesLoader` class which allows for easier
testing of code that works with a `SpringFactoriesLoader`.

Closes gh-28416

spring-core-test/src/main/java/org/springframework/core/mock/MockSpringFactoriesLoader.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright 2002-2022 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.core.mock;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.springframework.core.io.support.SpringFactoriesLoader;
+import org.springframework.lang.Nullable;
+
+/**
+ * Simple mock {@link SpringFactoriesLoader} implementation that can be used for testing
+ * purposes.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ */
+public class MockSpringFactoriesLoader extends SpringFactoriesLoader {
+
+	private final AtomicInteger sequence = new AtomicInteger();
+
+	private final Map<String, List<String>> factories;
+
+	private final Map<String, Object> implementations = new HashMap<>();
+
+
+	/**
+	 * Create a new {@link MockSpringFactoriesLoader} instance with the default
+	 * classloader.
+	 */
+	public MockSpringFactoriesLoader() {
+		this(null);
+	}
+
+	/**
+	 * Create a new {@link MockSpringFactoriesLoader} instance with the given classloader.
+	 * @param classLoader the classloader to use
+	 */
+	public MockSpringFactoriesLoader(@Nullable ClassLoader classLoader) {
+		this(classLoader, new LinkedHashMap<>());
+	}
+
+	protected MockSpringFactoriesLoader(ClassLoader classLoader, Map<String, List<String>> factories) {
+		super(classLoader, factories);
+		this.factories = factories;
+	}
+
+
+	@Override
+	@SuppressWarnings("unchecked")
+	protected <T> T instantiateFactory(String implementationName, Class<T> type, ArgumentResolver argumentResolver,
+			FailureHandler failureHandler) {
+		if (implementationName.startsWith("!")) {
+			Object implementation = this.implementations.get(implementationName);
+			if (implementation != null) {
+				return (T) implementation;
+			}
+		}
+		return super.instantiateFactory(implementationName, type, argumentResolver, failureHandler);
+	}
+
+	/**
+	 * Add factory implementations to this instance.
+	 * @param factoryType the factory type class
+	 * @param factoryImplementations the implementation classes
+	 */
+	@SafeVarargs
+	@SuppressWarnings("unchecked")
+	public final <T> void add(Class<T> factoryType, Class<? extends T>... factoryImplementations) {
+		for (Class<? extends T> factoryImplementation : factoryImplementations) {
+			add(factoryType.getName(), factoryImplementation.getName());
+		}
+	}
+
+	/**
+	 * Add factory implementations to this instance.
+	 * @param factoryType the factory type class name
+	 * @param factoryImplementations the implementation class names
+	 */
+	public void add(String factoryType, String... factoryImplementations) {
+		List<String> implementations = this.factories.computeIfAbsent(factoryType, key -> new ArrayList<>());
+		for (String factoryImplementation : factoryImplementations) {
+			implementations.add(factoryImplementation);
+		}
+	}
+
+	/**
+	 * Add factory instances to this instance.
+	 * @param factoryType the factory type class
+	 * @param factoryInstances the implementation instances to add
+	 */
+	@SuppressWarnings("unchecked")
+	public <T> void addInstance(Class<T> factoryType, T... factoryInstances) {
+		addInstance(factoryType.getName(), factoryInstances);
+	}
+
+	/**
+	 * Add factory instances to this instance.
+	 * @param factoryType the factory type class name
+	 * @param factoryInstance the implementation instances to add
+	 */
+	@SuppressWarnings("unchecked")
+	public <T> void addInstance(String factoryType, T... factoryInstance) {
+		List<String> implementations = this.factories.computeIfAbsent(factoryType, key -> new ArrayList<>());
+		for (T factoryImplementation : factoryInstance) {
+			String reference = "!" + factoryType + ":" + factoryImplementation.getClass().getName()
+					+ this.sequence.getAndIncrement();
+			implementations.add(reference);
+			this.implementations.put(reference, factoryImplementation);
+		}
+	}
+
+}

spring-core-test/src/test/java/org/springframework/core/mock/MockSpringFactoriesLoaderTests.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2002-2022 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.core.mock;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.annotation.Order;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link MockSpringFactoriesLoader}.
+ *
+ * @author Phillip Webb
+ */
+class MockSpringFactoriesLoaderTests {
+
+	@Test
+	void addWithClassesAddsFactories() {
+		MockSpringFactoriesLoader loader = new MockSpringFactoriesLoader();
+		loader.add(TestFactoryType.class, TestFactoryOne.class, TestFactoryTwo.class);
+		assertThatLoaderHasTestFactories(loader);
+	}
+
+	@Test
+	void addWithClassNamesAddsFactories() {
+		MockSpringFactoriesLoader loader = new MockSpringFactoriesLoader();
+		loader.add(TestFactoryType.class.getName(), TestFactoryOne.class.getName(), TestFactoryTwo.class.getName());
+		assertThatLoaderHasTestFactories(loader);
+	}
+
+	@Test
+	void addWithClassAndInstancesAddsFactories() {
+		MockSpringFactoriesLoader loader = new MockSpringFactoriesLoader();
+		loader.addInstance(TestFactoryType.class, new TestFactoryOne(), new TestFactoryTwo());
+		assertThatLoaderHasTestFactories(loader);
+	}
+
+	@Test
+	void addWithClassNameAndInstancesAddsFactories() {
+		MockSpringFactoriesLoader loader = new MockSpringFactoriesLoader();
+		loader.addInstance(TestFactoryType.class.getName(), new TestFactoryOne(), new TestFactoryTwo());
+		assertThatLoaderHasTestFactories(loader);
+	}
+
+	private void assertThatLoaderHasTestFactories(MockSpringFactoriesLoader loader) {
+		List<TestFactoryType> factories = loader.load(TestFactoryType.class);
+		assertThat(factories).hasSize(2);
+		assertThat(factories.get(0)).isInstanceOf(TestFactoryOne.class);
+		assertThat(factories.get(1)).isInstanceOf(TestFactoryTwo.class);
+	}
+
+	static interface TestFactoryType {
+
+	}
+
+	@Order(1)
+	static class TestFactoryOne implements TestFactoryType {
+
+	}
+
+	@Order(2)
+	static class TestFactoryTwo implements TestFactoryType {
+
+	}
+
+}