Deprecate Bootstrapper

Deprecate the `Bootstrapper` interface entirely and provide a
`BootstrapRegistryInitializer` alternative so that people can migrate.

Unfortunately our previous attempt to fix the typo in the `Bootstrapper`
interface didn't provide us a way to remove the deprecated method
without impacting users. It was also problematic for people who were
implementing `Bootstrapper` rather than using a lambda since they needed
to introduce the deprecated method.

We unfortunately can't see a way to fix the original typo without
introducing a new interface.

Fixes gh-25735

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/BootstrapRegistryInitializer.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2012-2021 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.boot;
+
+/**
+ * Callback interface that can be used to initialize a {@link BootstrapRegistry} before it
+ * is used.
+ *
+ * @author Phillip Webb
+ * @since 2.4.5
+ * @see SpringApplication#addBootstrapRegistryInitializer(BootstrapRegistryInitializer)
+ * @see BootstrapRegistry
+ */
+@FunctionalInterface
+public interface BootstrapRegistryInitializer {
+
+	/**
+	 * Initialize the given {@link BootstrapRegistry} with any required registrations.
+	 * @param registry the registry to initialize
+	 */
+	void initialize(BootstrapRegistry registry);
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/Bootstrapper.java

@@ -24,7 +24,9 @@ package org.springframework.boot;
  * @since 2.4.0
  * @see SpringApplication#addBootstrapper(Bootstrapper)
  * @see BootstrapRegistry
+ * @deprecated since 2.4.5 in favor of {@link BootstrapRegistryInitializer}
  */
+@Deprecated
 public interface Bootstrapper {
 
 	/**

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -236,7 +236,7 @@ public class SpringApplication {
 
 	private Map<String, Object> defaultProperties;
 
-	private List<Bootstrapper> bootstrappers;
+	private List<BootstrapRegistryInitializer> bootstrapRegistryInitializers;
 
 	private Set<String> additionalProfiles = Collections.emptySet();
 
@@ -280,12 +280,22 @@ public class SpringApplication {
 		Assert.notNull(primarySources, "PrimarySources must not be null");
 		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
 		this.webApplicationType = WebApplicationType.deduceFromClasspath();
-		this.bootstrappers = new ArrayList<>(getSpringFactoriesInstances(Bootstrapper.class));
+		this.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();
 		setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
 		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
 		this.mainApplicationClass = deduceMainApplicationClass();
 	}
 
+	@SuppressWarnings("deprecation")
+	private List<BootstrapRegistryInitializer> getBootstrapRegistryInitializersFromSpringFactories() {
+		ArrayList<BootstrapRegistryInitializer> initializers = new ArrayList<>();
+		getSpringFactoriesInstances(Bootstrapper.class).stream()
+				.map((bootstrapper) -> ((BootstrapRegistryInitializer) bootstrapper::initialize))
+				.forEach(initializers::add);
+		initializers.addAll(getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
+		return initializers;
+	}
+
 	private Class<?> deduceMainApplicationClass() {
 		try {
 			StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
@@ -349,7 +359,7 @@ public class SpringApplication {
 
 	private DefaultBootstrapContext createBootstrapContext() {
 		DefaultBootstrapContext bootstrapContext = new DefaultBootstrapContext();
-		this.bootstrappers.forEach((initializer) -> initializer.initialize(bootstrapContext));
+		this.bootstrapRegistryInitializers.forEach((initializer) -> initializer.initialize(bootstrapContext));
 		return bootstrapContext;
 	}
 
@@ -1054,10 +1064,24 @@ public class SpringApplication {
 	 * {@link BootstrapRegistry}.
 	 * @param bootstrapper the bootstraper
 	 * @since 2.4.0
+	 * @deprecated since 2.4.5 in favor of
+	 * {@link #addBootstrapRegistryInitializer(BootstrapRegistryInitializer)}
 	 */
+	@Deprecated
 	public void addBootstrapper(Bootstrapper bootstrapper) {
 		Assert.notNull(bootstrapper, "Bootstrapper must not be null");
-		this.bootstrappers.add(bootstrapper);
+		this.bootstrapRegistryInitializers.add(bootstrapper::initialize);
+	}
+
+	/**
+	 * Adds {@link BootstrapRegistryInitializer} instances that can be used to initialize
+	 * the {@link BootstrapRegistry}.
+	 * @param bootstrapRegistryInitializer the bootstrap registry initializer to add
+	 * @since 2.4.5
+	 */
+	public void addBootstrapRegistryInitializer(BootstrapRegistryInitializer bootstrapRegistryInitializer) {
+		Assert.notNull(bootstrapRegistryInitializer, "BootstrapRegistryInitializer must not be null");
+		this.bootstrapRegistryInitializers.addAll(Arrays.asList(bootstrapRegistryInitializer));
 	}
 
 	/**

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/builder/SpringApplicationBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -31,7 +31,7 @@ import org.springframework.beans.factory.support.BeanNameGenerator;
 import org.springframework.boot.ApplicationContextFactory;
 import org.springframework.boot.Banner;
 import org.springframework.boot.BootstrapRegistry;
-import org.springframework.boot.Bootstrapper;
+import org.springframework.boot.BootstrapRegistryInitializer;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.WebApplicationType;
 import org.springframework.boot.convert.ApplicationConversionService;
@@ -400,17 +400,33 @@ public class SpringApplicationBuilder {
 	}
 
 	/**
-	 * Adds a {@link Bootstrapper} that can be used to initialize the
-	 * {@link BootstrapRegistry}.
+	 * Adds a {@link org.springframework.boot.Bootstrapper} that can be used to initialize
+	 * the {@link BootstrapRegistry}.
 	 * @param bootstrapper the bootstraper
 	 * @return the current builder
 	 * @since 2.4.0
+	 * @deprecated since 2.4.5 in favor of
+	 * {@link #addBootstrapRegistryInitializer(BootstrapRegistryInitializer)}
 	 */
-	public SpringApplicationBuilder addBootstrapper(Bootstrapper bootstrapper) {
+	@Deprecated
+	public SpringApplicationBuilder addBootstrapper(org.springframework.boot.Bootstrapper bootstrapper) {
 		this.application.addBootstrapper(bootstrapper);
 		return this;
 	}
 
+	/**
+	 * Adds {@link BootstrapRegistryInitializer} instances that can be used to initialize
+	 * the {@link BootstrapRegistry}.
+	 * @param bootstrapRegistryInitializer the bootstrap registry initializer to add
+	 * @return the current builder
+	 * @since 2.4.5
+	 */
+	public SpringApplicationBuilder addBootstrapRegistryInitializer(
+			BootstrapRegistryInitializer bootstrapRegistryInitializer) {
+		this.application.addBootstrapRegistryInitializer(bootstrapRegistryInitializer);
+		return this;
+	}
+
 	/**
 	 * Flag to control whether the application should be initialized lazily.
 	 * @param lazyInitialization the flag to set. Defaults to false.

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java

@@ -1219,10 +1219,10 @@ class SpringApplicationTests {
 	}
 
 	@Test
-	void addBootstrapper() {
+	void addBootstrapRegistryInitializer() {
 		SpringApplication application = new SpringApplication(ExampleConfig.class);
 		application.setWebApplicationType(WebApplicationType.NONE);
-		application.addBootstrapper(
+		application.addBootstrapRegistryInitializer(
 				(bootstrapContext) -> bootstrapContext.register(String.class, InstanceSupplier.of("boot")));
 		TestApplicationListener listener = new TestApplicationListener();
 		application.addListeners(listener);
@@ -1235,10 +1235,10 @@ class SpringApplicationTests {
 	}
 
 	@Test
-	void addBootstrapperCanRegisterBeans() {
+	void addBootstrapRegistryInitializerCanRegisterBeans() {
 		SpringApplication application = new SpringApplication(ExampleConfig.class);
 		application.setWebApplicationType(WebApplicationType.NONE);
-		application.addBootstrapper((bootstrapContext) -> {
+		application.addBootstrapRegistryInitializer((bootstrapContext) -> {
 			bootstrapContext.register(String.class, InstanceSupplier.of("boot"));
 			bootstrapContext.addCloseListener((event) -> event.getApplicationContext().getBeanFactory()
 					.registerSingleton("test", event.getBootstrapContext().get(String.class)));
@@ -1248,6 +1248,7 @@ class SpringApplicationTests {
 	}
 
 	@Test
+	@Deprecated
 	void whenABootstrapperImplementsOnlyTheOldMethodThenItIsCalled() {
 		SpringApplication application = new SpringApplication(ExampleConfig.class);
 		application.setWebApplicationType(WebApplicationType.NONE);
@@ -1259,6 +1260,7 @@ class SpringApplicationTests {
 	}
 
 	@Test
+	@Deprecated
 	void whenABootstrapperImplementsTheOldMethodAndTheNewMethodThenOnlyTheNewMethodIsCalled() {
 		SpringApplication application = new SpringApplication(ExampleConfig.class);
 		application.setWebApplicationType(WebApplicationType.NONE);
@@ -1743,18 +1745,19 @@ class SpringApplicationTests {
 
 	}
 
+	@Deprecated
 	static class OnlyOldMethodTestBootstrapper implements Bootstrapper {
 
 		private boolean intitialized;
 
 		@Override
-		@SuppressWarnings("deprecation")
 		public void intitialize(BootstrapRegistry registry) {
 			this.intitialized = true;
 		}
 
 	}
 
+	@Deprecated
 	static class BothMethodsTestBootstrapper implements Bootstrapper {
 
 		private boolean intitialized;
@@ -1762,7 +1765,6 @@ class SpringApplicationTests {
 		private boolean initialized;
 
 		@Override
-		@SuppressWarnings("deprecation")
 		public void intitialize(BootstrapRegistry registry) {
 			this.intitialized = true;
 		}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/builder/SpringApplicationBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -283,6 +283,7 @@ class SpringApplicationBuilderTests {
 	}
 
 	@Test
+	@Deprecated
 	void addBootstrapper() {
 		SpringApplicationBuilder application = new SpringApplicationBuilder(ExampleConfig.class)
 				.web(WebApplicationType.NONE).addBootstrapper((context) -> context.addCloseListener(
@@ -291,6 +292,15 @@ class SpringApplicationBuilderTests {
 		assertThat(this.context.getBean("test")).isEqualTo("spring");
 	}
 
+	@Test
+	void addBootstrapRegistryInitializer() {
+		SpringApplicationBuilder application = new SpringApplicationBuilder(ExampleConfig.class)
+				.web(WebApplicationType.NONE).addBootstrapRegistryInitializer((context) -> context.addCloseListener(
+						(event) -> event.getApplicationContext().getBeanFactory().registerSingleton("test", "spring")));
+		this.context = application.run();
+		assertThat(this.context.getBean("test")).isEqualTo("spring");
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class ExampleConfig {
 

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-bootstrap-registry/src/main/java/smoketest/bootstrapregistry/app/SampleBootstrapRegistryApplication.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -29,7 +29,7 @@ public class SampleBootstrapRegistryApplication {
 		// SubversionClient that still has access to data provided in the
 		// application.properties file
 		SpringApplication application = new SpringApplication(SampleBootstrapRegistryApplication.class);
-		application.addBootstrapper(SubversionBootstrap.withCustomClient(MySubversionClient::new));
+		application.addBootstrapRegistryInitializer(SubversionBootstrap.withCustomClient(MySubversionClient::new));
 		application.run(args);
 	}
 

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-bootstrap-registry/src/main/java/smoketest/bootstrapregistry/external/svn/SubversionBootstrap.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -19,10 +19,10 @@ package smoketest.bootstrapregistry.external.svn;
 import java.util.function.Function;
 
 import org.springframework.boot.BootstrapContext;
-import org.springframework.boot.Bootstrapper;
+import org.springframework.boot.BootstrapRegistryInitializer;
 
 /**
- * Allows the user to register a {@link Bootstrapper} with a custom
+ * Allows the user to register a {@link BootstrapRegistryInitializer} with a custom
  * {@link SubversionClient}.
  *
  * @author Phillip Webb
@@ -33,11 +33,12 @@ public final class SubversionBootstrap {
 	}
 
 	/**
-	 * Return a {@link Bootstrapper} for the given client factory.
+	 * Return a {@link BootstrapRegistryInitializer} for the given client factory.
 	 * @param clientFactory the client factory
-	 * @return a {@link Bootstrapper} instance
+	 * @return a {@link BootstrapRegistryInitializer} instance
 	 */
-	public static Bootstrapper withCustomClient(Function<SubversionServerCertificate, SubversionClient> clientFactory) {
+	public static BootstrapRegistryInitializer withCustomClient(
+			Function<SubversionServerCertificate, SubversionClient> clientFactory) {
 		return (registry) -> registry.register(SubversionClient.class,
 				(bootstrapContext) -> createSubversionClient(bootstrapContext, clientFactory));
 	}