Remove use of @PostConstruct from main code

When running on Java 11 (where `@PostConstruct` is no longer part of
the JRE) and without a dependency on jakarta-annotation-api,
`@PostContruct` annotions are silently dropped. This leads to obscure and
hard-to-track down changes in the behaviour of our auto-configuration
as the `@PostConstruct`-annotated methods are not invoked.

To allow users to run on Java 11 without having jakarta-annotation-api
on the classpath, this commit removes use of `@PostConstruct` from main
code. A Checkstyle rule has also been added to prevent its usage in
main code from being reintroduced.

Closes gh-23723

Author: wilkinsona

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/jersey/JerseyWebEndpointManagementContextConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -21,8 +21,6 @@
 import java.util.HashSet;
 import java.util.List;
 
-import javax.annotation.PostConstruct;
-
 import org.glassfish.jersey.server.ResourceConfig;
 import org.glassfish.jersey.server.model.Resource;
 
@@ -112,10 +110,10 @@ static class JerseyWebEndpointsResourcesRegistrar {
 			this.mediaTypes = endpointMediaTypes;
 			this.basePath = basePath;
 			this.shouldRegisterLinks = shouldRegisterLinks;
+			register();
 		}
 
-		@PostConstruct
-		void register() {
+		private void register() {
 			// We can't easily use @ConditionalOnBean because @AutoConfigureBefore is
 			// not an option for management contexts. Instead we manually check if
 			// the resource config bean exists

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/cache/CacheMetricsRegistrarConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -19,8 +19,6 @@
 import java.util.Collection;
 import java.util.Map;
 
-import javax.annotation.PostConstruct;
-
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.Tag;
 
@@ -56,15 +54,15 @@ class CacheMetricsRegistrarConfiguration {
 		this.registry = registry;
 		this.cacheManagers = cacheManagers;
 		this.cacheMetricsRegistrar = new CacheMetricsRegistrar(this.registry, binderProviders);
+		bindCachesToRegistry();
 	}
 
 	@Bean
 	CacheMetricsRegistrar cacheMetricsRegistrar() {
 		return this.cacheMetricsRegistrar;
 	}
 
-	@PostConstruct
-	void bindCachesToRegistry() {
+	private void bindCachesToRegistry() {
 		this.cacheManagers.forEach(this::bindCacheManagerToRegistry);
 	}
 

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/batch/BasicBatchConfigurer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -16,7 +16,6 @@
 
 package org.springframework.boot.autoconfigure.batch;
 
-import javax.annotation.PostConstruct;
 import javax.sql.DataSource;
 
 import org.springframework.batch.core.configuration.annotation.BatchConfigurer;
@@ -26,6 +25,7 @@
 import org.springframework.batch.core.launch.support.SimpleJobLauncher;
 import org.springframework.batch.core.repository.JobRepository;
 import org.springframework.batch.core.repository.support.JobRepositoryFactoryBean;
+import org.springframework.beans.factory.InitializingBean;
 import org.springframework.boot.autoconfigure.transaction.TransactionManagerCustomizers;
 import org.springframework.boot.context.properties.PropertyMapper;
 import org.springframework.jdbc.datasource.DataSourceTransactionManager;
@@ -40,7 +40,7 @@
  * @author Stephane Nicoll
  * @since 1.0.0
  */
-public class BasicBatchConfigurer implements BatchConfigurer {
+public class BasicBatchConfigurer implements BatchConfigurer, InitializingBean {
 
 	private final BatchProperties properties;
 
@@ -90,7 +90,11 @@ public JobExplorer getJobExplorer() throws Exception {
 		return this.jobExplorer;
 	}
 
-	@PostConstruct
+	@Override
+	public void afterPropertiesSet() {
+		initialize();
+	}
+
 	public void initialize() {
 		try {
 			this.transactionManager = buildTransactionManager();

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/freemarker/FreeMarkerAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -19,8 +19,6 @@
 import java.util.ArrayList;
 import java.util.List;
 
-import javax.annotation.PostConstruct;
-
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
@@ -57,9 +55,9 @@ public class FreeMarkerAutoConfiguration {
 	public FreeMarkerAutoConfiguration(ApplicationContext applicationContext, FreeMarkerProperties properties) {
 		this.applicationContext = applicationContext;
 		this.properties = properties;
+		checkTemplateLocationExists();
 	}
 
-	@PostConstruct
 	public void checkTemplateLocationExists() {
 		if (logger.isWarnEnabled() && this.properties.isCheckTemplateLocation()) {
 			List<TemplateLocation> locations = getLocations();

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/groovy/template/GroovyTemplateAutoConfiguration.java

@@ -19,7 +19,6 @@
 import java.security.CodeSource;
 import java.security.ProtectionDomain;
 
-import javax.annotation.PostConstruct;
 import javax.servlet.Servlet;
 
 import groovy.text.markup.MarkupTemplateEngine;
@@ -77,9 +76,9 @@ public static class GroovyMarkupConfiguration {
 		public GroovyMarkupConfiguration(ApplicationContext applicationContext, GroovyTemplateProperties properties) {
 			this.applicationContext = applicationContext;
 			this.properties = properties;
+			checkTemplateLocationExists();
 		}
 
-		@PostConstruct
 		public void checkTemplateLocationExists() {
 			if (this.properties.isCheckTemplateLocation() && !isUsingGroovyAllJar()) {
 				TemplateLocation location = new TemplateLocation(this.properties.getResourceLoaderPath());

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/hateoas/HypermediaHttpMessageConverterConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -20,11 +20,10 @@
 import java.util.Collection;
 import java.util.List;
 
-import javax.annotation.PostConstruct;
-
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.beans.factory.InitializingBean;
 import org.springframework.beans.factory.ListableBeanFactory;
 import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
@@ -60,12 +59,13 @@ public static HalMessageConverterSupportedMediaTypesCustomizer halMessageConvert
 	 * {@code Jackson2ModuleRegisteringBeanPostProcessor} has registered the converter and
 	 * it is unordered.
 	 */
-	private static class HalMessageConverterSupportedMediaTypesCustomizer implements BeanFactoryAware {
+	private static class HalMessageConverterSupportedMediaTypesCustomizer
+			implements BeanFactoryAware, InitializingBean {
 
 		private volatile BeanFactory beanFactory;
 
-		@PostConstruct
-		void configureHttpMessageConverters() {
+		@Override
+		public void afterPropertiesSet() {
 			if (this.beanFactory instanceof ListableBeanFactory) {
 				configureHttpMessageConverters(((ListableBeanFactory) this.beanFactory)
 						.getBeansOfType(RequestMappingHandlerAdapter.class).values());

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/DataSourceJmxConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -18,7 +18,6 @@
 
 import java.sql.SQLException;
 
-import javax.annotation.PostConstruct;
 import javax.sql.DataSource;
 
 import com.zaxxer.hikari.HikariDataSource;
@@ -59,10 +58,10 @@ static class Hikari {
 		Hikari(DataSource dataSource, ObjectProvider<MBeanExporter> mBeanExporter) {
 			this.dataSource = dataSource;
 			this.mBeanExporter = mBeanExporter;
+			validateMBeans();
 		}
 
-		@PostConstruct
-		void validateMBeans() {
+		private void validateMBeans() {
 			HikariDataSource hikariDataSource = DataSourceUnwrapper.unwrap(this.dataSource, HikariDataSource.class);
 			if (hikariDataSource != null && hikariDataSource.isRegisterMbeans()) {
 				this.mBeanExporter.ifUnique((exporter) -> exporter.addExcludedBean("dataSource"));

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jersey/JerseyAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -19,7 +19,6 @@
 import java.util.Collections;
 import java.util.EnumSet;
 
-import javax.annotation.PostConstruct;
 import javax.servlet.DispatcherType;
 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
@@ -95,22 +94,11 @@ public class JerseyAutoConfiguration implements ServletContextAware {
 
 	private final ResourceConfig config;
 
-	private final ObjectProvider<ResourceConfigCustomizer> customizers;
-
 	public JerseyAutoConfiguration(JerseyProperties jersey, ResourceConfig config,
 			ObjectProvider<ResourceConfigCustomizer> customizers) {
 		this.jersey = jersey;
 		this.config = config;
-		this.customizers = customizers;
-	}
-
-	@PostConstruct
-	public void path() {
-		customize();
-	}
-
-	private void customize() {
-		this.customizers.orderedStream().forEach((customizer) -> customizer.customize(this.config));
+		customizers.orderedStream().forEach((customizer) -> customizer.customize(this.config));
 	}
 
 	@Bean

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mail/MailSenderValidatorAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -16,7 +16,6 @@
 
 package org.springframework.boot.autoconfigure.mail;
 
-import javax.annotation.PostConstruct;
 import javax.mail.MessagingException;
 
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
@@ -44,9 +43,9 @@ public class MailSenderValidatorAutoConfiguration {
 
 	public MailSenderValidatorAutoConfiguration(JavaMailSenderImpl mailSender) {
 		this.mailSender = mailSender;
+		validateConnection();
 	}
 
-	@PostConstruct
 	public void validateConnection() {
 		try {
 			this.mailSender.testConnection();

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mustache/MustacheAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -16,8 +16,6 @@
 
 package org.springframework.boot.autoconfigure.mustache;
 
-import javax.annotation.PostConstruct;
-
 import com.samskivert.mustache.Mustache;
 import com.samskivert.mustache.Mustache.Collector;
 import com.samskivert.mustache.Mustache.TemplateLoader;
@@ -57,9 +55,9 @@ public class MustacheAutoConfiguration {
 	public MustacheAutoConfiguration(MustacheProperties mustache, ApplicationContext applicationContext) {
 		this.mustache = mustache;
 		this.applicationContext = applicationContext;
+		checkTemplateLocationExists();
 	}
 
-	@PostConstruct
 	public void checkTemplateLocationExists() {
 		if (this.mustache.isCheckTemplateLocation()) {
 			TemplateLocation location = new TemplateLocation(this.mustache.getPrefix());