/*
 * Copyright 2002-2020 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.
 * 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.context.support;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.beans.BeansException;
import org.springframework.beans.CachedIntrospectionResults;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.ObjectProvider;
import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.support.ResourceEditorRegistrar;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.context.ApplicationListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.EmbeddedValueResolverAware;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.HierarchicalMessageSource;
import org.springframework.context.LifecycleProcessor;
import org.springframework.context.MessageSource;
import org.springframework.context.MessageSourceAware;
import org.springframework.context.MessageSourceResolvable;
import org.springframework.context.NoSuchMessageException;
import org.springframework.context.PayloadApplicationEvent;
import org.springframework.context.ResourceLoaderAware;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.ContextClosedEvent;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.context.event.ContextStartedEvent;
import org.springframework.context.event.ContextStoppedEvent;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.context.expression.StandardBeanExpressionResolver;
import org.springframework.context.weaving.LoadTimeWeaverAware;
import org.springframework.context.weaving.LoadTimeWeaverAwareProcessor;
import org.springframework.core.ResolvableType;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.core.convert.ConversionService;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.Environment;
import org.springframework.core.env.StandardEnvironment;
import org.springframework.core.io.DefaultResourceLoader;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;

/**
 * Abstract implementation of the {@link org.springframework.context.ApplicationContext}
 * interface. Doesn't mandate the type of storage used for configuration; simply
 * implements common context functionality. Uses the Template Method design pattern,
 * requiring concrete subclasses to implement abstract methods.
 *
 * <p>In contrast to a plain BeanFactory, an ApplicationContext is supposed
 * to detect special beans defined in its internal bean factory:
 * Therefore, this class automatically registers
 * {@link org.springframework.beans.factory.config.BeanFactoryPostProcessor BeanFactoryPostProcessors},
 * {@link org.springframework.beans.factory.config.BeanPostProcessor BeanPostProcessors},
 * and {@link org.springframework.context.ApplicationListener ApplicationListeners}
 * which are defined as beans in the context.
 *
 * <p>A {@link org.springframework.context.MessageSource} may also be supplied
 * as a bean in the context, with the name "messageSource"; otherwise, message
 * resolution is delegated to the parent context. Furthermore, a multicaster
 * for application events can be supplied as an "applicationEventMulticaster" bean
 * of type {@link org.springframework.context.event.ApplicationEventMulticaster}
 * in the context; otherwise, a default multicaster of type
 * {@link org.springframework.context.event.SimpleApplicationEventMulticaster} will be used.
 *
 * <p>Implements resource loading by extending
 * {@link org.springframework.core.io.DefaultResourceLoader}.
 * Consequently treats non-URL resource paths as class path resources
 * (supporting full class path resource names that include the package path,
 * e.g. "mypackage/myresource.dat"), unless the {@link #getResourceByPath}
 * method is overridden in a subclass.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Mark Fisher
 * @author Stephane Nicoll
 * @author Sam Brannen
 * @since January 21, 2001
 * @see #refreshBeanFactory
 * @see #getBeanFactory
 * @see org.springframework.beans.factory.config.BeanFactoryPostProcessor
 * @see org.springframework.beans.factory.config.BeanPostProcessor
 * @see org.springframework.context.event.ApplicationEventMulticaster
 * @see org.springframework.context.ApplicationListener
 * @see org.springframework.context.MessageSource
 */
public abstract class AbstractApplicationContext extends DefaultResourceLoader
                implements ConfigurableApplicationContext {

        /**
         * Name of the MessageSource bean in the factory.
         * If none is supplied, message resolution is delegated to the parent.
         * @see MessageSource
         */
        public static final String MESSAGE_SOURCE_BEAN_NAME = "messageSource";

        /**
         * Name of the LifecycleProcessor bean in the factory.
         * If none is supplied, a DefaultLifecycleProcessor is used.
         * @see org.springframework.context.LifecycleProcessor
         * @see org.springframework.context.support.DefaultLifecycleProcessor
         */
        public static final String LIFECYCLE_PROCESSOR_BEAN_NAME = "lifecycleProcessor";

        /**
         * Name of the ApplicationEventMulticaster bean in the factory.
         * If none is supplied, a default SimpleApplicationEventMulticaster is used.
         * @see org.springframework.context.event.ApplicationEventMulticaster
         * @see org.springframework.context.event.SimpleApplicationEventMulticaster
         */
        public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";


        static {
                // Eagerly load the ContextClosedEvent class to avoid weird classloader issues
                // on application shutdown in WebLogic 8.1. (Reported by Dustin Woods.)
                ContextClosedEvent.class.getName();
        }


        /** Logger used by this class. Available to subclasses. */
        protected final Log logger = LogFactory.getLog(getClass());

        /** Unique id for this context, if any. */
        private String id = ObjectUtils.identityToString(this);

        /** Display name. */
        private String displayName = ObjectUtils.identityToString(this);

        /** Parent context. */
        @Nullable
        private ApplicationContext parent;

        /** Environment used by this context. */
        @Nullable
        private ConfigurableEnvironment environment;

        /** BeanFactoryPostProcessors to apply on refresh. */
        private final List<BeanFactoryPostProcessor> beanFactoryPostProcessors = new ArrayList<>();

        /** System time in milliseconds when this context started. */
        private long startupDate;

        /** Flag that indicates whether this context is currently active. */
        private final AtomicBoolean active = new AtomicBoolean();

        /** Flag that indicates whether this context has been closed already. */
        private final AtomicBoolean closed = new AtomicBoolean();

        /** Synchronization monitor for the "refresh" and "destroy". */
        private final Object startupShutdownMonitor = new Object();

        /** Reference to the JVM shutdown hook, if registered. */
        @Nullable
        private Thread shutdownHook;

        /** ResourcePatternResolver used by this context. */
        private ResourcePatternResolver resourcePatternResolver;

        /** LifecycleProcessor for managing the lifecycle of beans within this context. */
        @Nullable
        private LifecycleProcessor lifecycleProcessor;

        /** MessageSource we delegate our implementation of this interface to. */
        @Nullable
        private MessageSource messageSource;

        /** Helper class used in event publishing. */
        @Nullable
        private ApplicationEventMulticaster applicationEventMulticaster;

        /** Statically specified listeners. */
        private final Set<ApplicationListener<?>> applicationListeners = new LinkedHashSet<>();

        /** Local listeners registered before refresh. */
        @Nullable
        private Set<ApplicationListener<?>> earlyApplicationListeners;

        /** ApplicationEvents published before the multicaster setup. */
        @Nullable
        private Set<ApplicationEvent> earlyApplicationEvents;


        /**
         * Create a new AbstractApplicationContext with no parent.
         */
        public AbstractApplicationContext() {
                this.resourcePatternResolver = getResourcePatternResolver();
        }

        /**
         * Create a new AbstractApplicationContext with the given parent context.
         * @param parent the parent context
         */
        public AbstractApplicationContext(@Nullable ApplicationContext parent) {
                this();
                setParent(parent);
        }


        //---------------------------------------------------------------------
        // Implementation of ApplicationContext interface
        //---------------------------------------------------------------------

        /**
         * Set the unique id of this application context.
         * <p>Default is the object id of the context instance, or the name
         * of the context bean if the context is itself defined as a bean.
         * @param id the unique id of the context
         */
        @Override
        public void setId(String id) {
                this.id = id;
        }

        @Override
        public String getId() {
                return this.id;
        }

        @Override
        public String getApplicationName() {
                return "";
        }

        /**
         * Set a friendly name for this context.
         * Typically done during initialization of concrete context implementations.
         * <p>Default is the object id of the context instance.
         */
        public void setDisplayName(String displayName) {
                Assert.hasLength(displayName, "Display name must not be empty");
                this.displayName = displayName;
        }

        /**
         * Return a friendly name for this context.
         * @return a display name for this context (never {@code null})
         */
        @Override
        public String getDisplayName() {
                return this.displayName;
        }

        /**
         * Return the parent context, or {@code null} if there is no parent
         * (that is, this context is the root of the context hierarchy).
         */
        @Override
        @Nullable
        public ApplicationContext getParent() {
                return this.parent;
        }

        /**
         * Set the {@code Environment} for this application context.
         * <p>Default value is determined by {@link #createEnvironment()}. Replacing the
         * default with this method is one option but configuration through {@link
         * #getEnvironment()} should also be considered. In either case, such modifications
         * should be performed <em>before</em> {@link #refresh()}.
         * @see org.springframework.context.support.AbstractApplicationContext#createEnvironment
         */
        @Override
        public void setEnvironment(ConfigurableEnvironment environment) {
                this.environment = environment;
        }

        /**
         * Return the {@code Environment} for this application context in configurable
         * form, allowing for further customization.
         * <p>If none specified, a default environment will be initialized via
         * {@link #createEnvironment()}.
         */
        @Override
        public ConfigurableEnvironment getEnvironment() {
                if (this.environment == null) {
                        this.environment = createEnvironment();
                }
                return this.environment;
        }

        /**
         * Create and return a new {@link StandardEnvironment}.
         * <p>Subclasses may override this method in order to supply
         * a custom {@link ConfigurableEnvironment} implementation.
         */
        protected ConfigurableEnvironment createEnvironment() {
                return new StandardEnvironment();
        }

        /**
         * Return this context's internal bean factory as AutowireCapableBeanFactory,
         * if already available.
         * @see #getBeanFactory()
         */
        @Override
        public AutowireCapableBeanFactory getAutowireCapableBeanFactory() throws IllegalStateException {
                return getBeanFactory();
        }

        /**
         * Return the timestamp (ms) when this context was first loaded.
         */
        @Override
        public long getStartupDate() {
                return this.startupDate;
        }

        /**
         * Publish the given event to all listeners.
         * <p>Note: Listeners get initialized after the MessageSource, to be able
         * to access it within listener implementations. Thus, MessageSource
         * implementations cannot publish events.
         * @param event the event to publish (may be application-specific or a
         * standard framework event)
         */
        @Override
        public void publishEvent(ApplicationEvent event) {
                publishEvent(event, null);
        }

        /**
         * Publish the given event to all listeners.
         * <p>Note: Listeners get initialized after the MessageSource, to be able
         * to access it within listener implementations. Thus, MessageSource
         * implementations cannot publish events.
         * @param event the event to publish (may be an {@link ApplicationEvent}
         * or a payload object to be turned into a {@link PayloadApplicationEvent})
         */
        @Override
        public void publishEvent(Object event) {
                publishEvent(event, null);
        }

        /**
         * Publish the given event to all listeners.
         * @param event the event to publish (may be an {@link ApplicationEvent}
         * or a payload object to be turned into a {@link PayloadApplicationEvent})
         * @param eventType the resolved event type, if known
         * @since 4.2
         */
        protected void publishEvent(Object event, @Nullable ResolvableType eventType) {
                Assert.notNull(event, "Event must not be null");

                // Decorate event as an ApplicationEvent if necessary
                ApplicationEvent applicationEvent;
                if (event instanceof ApplicationEvent) {
                        applicationEvent = (ApplicationEvent) event;
                }
                else {
                        applicationEvent = new PayloadApplicationEvent<>(this, event);
                        if (eventType == null) {
                                eventType = ((PayloadApplicationEvent<?>) applicationEvent).getResolvableType();
                        }
                }

                // Multicast right now if possible - or lazily once the multicaster is initialized
                if (this.earlyApplicationEvents != null) {
                        this.earlyApplicationEvents.add(applicationEvent);
                }
                else {
                        getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
                }

                // Publish event via parent context as well...
                if (this.parent != null) {
                        if (this.parent instanceof AbstractApplicationContext) {
                                ((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
                        }
                        else {
                                this.parent.publishEvent(event);
                        }
                }
        }

        /**
         * Return the internal ApplicationEventMulticaster used by the context.
         * @return the internal ApplicationEventMulticaster (never {@code null})
         * @throws IllegalStateException if the context has not been initialized yet
         */
        ApplicationEventMulticaster getApplicationEventMulticaster() throws IllegalStateException {
                if (this.applicationEventMulticaster == null) {
                        throw new IllegalStateException("ApplicationEventMulticaster not initialized - " +
                                        "call 'refresh' before multicasting events via the context: " + this);
                }
                return this.applicationEventMulticaster;
        }

        /**
         * Return the internal LifecycleProcessor used by the context.
         * @return the internal LifecycleProcessor (never {@code null})
         * @throws IllegalStateException if the context has not been initialized yet
         */
        LifecycleProcessor getLifecycleProcessor() throws IllegalStateException {
                if (this.lifecycleProcessor == null) {
                        throw new IllegalStateException("LifecycleProcessor not initialized - " +
                                        "call 'refresh' before invoking lifecycle methods via the context: " + this);
                }
                return this.lifecycleProcessor;
        }

        /**
         * Return the ResourcePatternResolver to use for resolving location patterns
         * into Resource instances. Default is a
         * {@link org.springframework.core.io.support.PathMatchingResourcePatternResolver},
         * supporting Ant-style location patterns.
         * <p>Can be overridden in subclasses, for extended resolution strategies,
         * for example in a web environment.
         * <p><b>Do not call this when needing to resolve a location pattern.</b>
         * Call the context's {@code getResources} method instead, which
         * will delegate to the ResourcePatternResolver.
         * @return the ResourcePatternResolver for this context
         * @see #getResources
         * @see org.springframework.core.io.support.PathMatchingResourcePatternResolver
         */
        protected ResourcePatternResolver getResourcePatternResolver() {
                return new PathMatchingResourcePatternResolver(this);
        }


        //---------------------------------------------------------------------
        // Implementation of ConfigurableApplicationContext interface
        //---------------------------------------------------------------------

        /**
         * Set the parent of this application context.
         * <p>The parent {@linkplain ApplicationContext#getEnvironment() environment} is
         * {@linkplain ConfigurableEnvironment#merge(ConfigurableEnvironment) merged} with
         * this (child) application context environment if the parent is non-{@code null} and
         * its environment is an instance of {@link ConfigurableEnvironment}.
         * @see ConfigurableEnvironment#merge(ConfigurableEnvironment)
         */
        @Override
        public void setParent(@Nullable ApplicationContext parent) {
                this.parent = parent;
                if (parent != null) {
                        Environment parentEnvironment = parent.getEnvironment();
                        if (parentEnvironment instanceof ConfigurableEnvironment) {
                                getEnvironment().merge((ConfigurableEnvironment) parentEnvironment);
                        }
                }
        }

        @Override
        public void addBeanFactoryPostProcessor(BeanFactoryPostProcessor postProcessor) {
                Assert.notNull(postProcessor, "BeanFactoryPostProcessor must not be null");
                this.beanFactoryPostProcessors.add(postProcessor);
        }

        /**
         * Return the list of BeanFactoryPostProcessors that will get applied
         * to the internal BeanFactory.
         */
        public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors() {
                return this.beanFactoryPostProcessors;
        }

        @Override
        public void addApplicationListener(ApplicationListener<?> listener) {
                Assert.notNull(listener, "ApplicationListener must not be null");
                if (this.applicationEventMulticaster != null) {
                        this.applicationEventMulticaster.addApplicationListener(listener);
                }
                this.applicationListeners.add(listener);
        }

        /**
         * Return the list of statically specified ApplicationListeners.
         */
        public Collection<ApplicationListener<?>> getApplicationListeners() {
                return this.applicationListeners;
        }

        @Override
        public void refresh() throws BeansException, IllegalStateException {
                synchronized (this.startupShutdownMonitor) {
                        // Prepare this context for refreshing.
                        prepareRefresh();

                        // Tell the subclass to refresh the internal bean factory.
                        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

                        // Prepare the bean factory for use in this context.
                        prepareBeanFactory(beanFactory);

                        try {
                                // Allows post-processing of the bean factory in context subclasses.
                                postProcessBeanFactory(beanFactory);

                                // Invoke factory processors registered as beans in the context.
                                invokeBeanFactoryPostProcessors(beanFactory);

                                // Register bean processors that intercept bean creation.
                                registerBeanPostProcessors(beanFactory);

                                // Initialize message source for this context.
                                initMessageSource();

                                // Initialize event multicaster for this context.
                                initApplicationEventMulticaster();

                                // Initialize other special beans in specific context subclasses.
                                onRefresh();

                                // Check for listener beans and register them.
                                registerListeners();

                                // Instantiate all remaining (non-lazy-init) singletons.
                                finishBeanFactoryInitialization(beanFactory);

                                // Last step: publish corresponding event.
                                finishRefresh();
                        }

                        catch (BeansException ex) {
                                if (logger.isWarnEnabled()) {
                                        logger.warn("Exception encountered during context initialization - " +
                                                        "cancelling refresh attempt: " + ex);
                                }

                                // Destroy already created singletons to avoid dangling resources.
                                destroyBeans();

                                // Reset 'active' flag.
                                cancelRefresh(ex);

                                // Propagate exception to caller.
                                throw ex;
                        }

                        finally {
                                // Reset common introspection caches in Spring's core, since we
                                // might not ever need metadata for singleton beans anymore...
                                resetCommonCaches();
                        }
                }
        }

        /**
         * Prepare this context for refreshing, setting its startup date and
         * active flag as well as performing any initialization of property sources.
         */
        protected void prepareRefresh() {
                // Switch to active.
                this.startupDate = System.currentTimeMillis();
                this.closed.set(false);
                this.active.set(true);

                if (logger.isDebugEnabled()) {
                        if (logger.isTraceEnabled()) {
                                logger.trace("Refreshing " + this);
                        }
                        else {
                                logger.debug("Refreshing " + getDisplayName());
                        }
                }

                // Initialize any placeholder property sources in the context environment.
                initPropertySources();

                // Validate that all properties marked as required are resolvable:
                // see ConfigurablePropertyResolver#setRequiredProperties
                getEnvironment().validateRequiredProperties();

                // Store pre-refresh ApplicationListeners...
                if (this.earlyApplicationListeners == null) {
                        this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
                }
                else {
                        // Reset local application listeners to pre-refresh state.
                        this.applicationListeners.clear();
                        this.applicationListeners.addAll(this.earlyApplicationListeners);
                }

                // Allow for the collection of early ApplicationEvents,
                // to be published once the multicaster is available...
                this.earlyApplicationEvents = new LinkedHashSet<>();
        }

        /**
         * <p>Replace any stub property sources with actual instances.
         * @see org.springframework.core.env.PropertySource.StubPropertySource
         * @see org.springframework.web.context.support.WebApplicationContextUtils#initServletPropertySources
         */
        protected void initPropertySources() {
                // For subclasses: do nothing by default.
        }

        /**
         * Tell the subclass to refresh the internal bean factory.
         * @return the fresh BeanFactory instance
         * @see #refreshBeanFactory()
         * @see #getBeanFactory()
         */
        protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
                refreshBeanFactory();
                return getBeanFactory();
        }

        /**
         * Configure the factory's standard context characteristics,
         * such as the context's ClassLoader and post-processors.
         * @param beanFactory the BeanFactory to configure
         */
        protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
                // Tell the internal bean factory to use the context's class loader etc.
                beanFactory.setBeanClassLoader(getClassLoader());
                beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
                beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

                // Configure the bean factory with context callbacks.
                beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
                beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
                beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
                beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
                beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
                beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
                beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

                // BeanFactory interface not registered as resolvable type in a plain factory.
                // MessageSource registered (and found for autowiring) as a bean.
                beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
                beanFactory.registerResolvableDependency(ResourceLoader.class, this);
                beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
                beanFactory.registerResolvableDependency(ApplicationContext.class, this);

                // Register early post-processor for detecting inner beans as ApplicationListeners.
                beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

                // Detect a LoadTimeWeaver and prepare for weaving, if found.
                if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
                        beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
                        // Set a temporary ClassLoader for type matching.
                        beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
                }

                // Register default environment beans.
                if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
                        beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
                }
                if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
                        beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
                }
                if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
                        beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
                }
        }

        /**
         * Modify the application context's internal bean factory after its standard
         * initialization. All bean definitions will have been loaded, but no beans
         * will have been instantiated yet. This allows for registering special
         * BeanPostProcessors etc in certain ApplicationContext implementations.
         * @param beanFactory the bean factory used by the application context
         */
        protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        }

        /**
         * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
         * respecting explicit order if given.
         * <p>Must be called before singleton instantiation.
         */
        protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
                PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

                // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
                // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
                if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
                        beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
                        beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
                }
        }

        /**
         * Instantiate and register all BeanPostProcessor beans,
         * respecting explicit order if given.
         * <p>Must be called before any instantiation of application beans.
         */
        protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
                PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
        }

        /**
         * Initialize the MessageSource.
         * Use parent's if none defined in this context.
         */
        protected void initMessageSource() {
                ConfigurableListableBeanFactory beanFactory = getBeanFactory();
                if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
                        this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
                        // Make MessageSource aware of parent MessageSource.
                        if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
                                HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
                                if (hms.getParentMessageSource() == null) {
                                        // Only set parent context as parent MessageSource if no parent MessageSource
                                        // registered already.
                                        hms.setParentMessageSource(getInternalParentMessageSource());
                                }
                        }
                        if (logger.isTraceEnabled()) {
                                logger.trace("Using MessageSource [" + this.messageSource + "]");
                        }
                }
                else {
                        // Use empty MessageSource to be able to accept getMessage calls.
                        DelegatingMessageSource dms = new DelegatingMessageSource();
                        dms.setParentMessageSource(getInternalParentMessageSource());
                        this.messageSource = dms;
                        beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
                        if (logger.isTraceEnabled()) {
                                logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");
                        }
                }
        }

        /**
         * Initialize the ApplicationEventMulticaster.
         * Uses SimpleApplicationEventMulticaster if none defined in the context.
         * @see org.springframework.context.event.SimpleApplicationEventMulticaster
         */
        protected void initApplicationEventMulticaster() {
                ConfigurableListableBeanFactory beanFactory = getBeanFactory();
                if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
                        this.applicationEventMulticaster =
                                        beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
                        if (logger.isTraceEnabled()) {
                                logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
                        }
                }
                else {
                        this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
                        beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
                        if (logger.isTraceEnabled()) {
                                logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
                                                "[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
                        }
                }
        }

        /**
         * Initialize the LifecycleProcessor.
         * Uses DefaultLifecycleProcessor if none defined in the context.
         * @see org.springframework.context.support.DefaultLifecycleProcessor
         */
        protected void initLifecycleProcessor() {
                ConfigurableListableBeanFactory beanFactory = getBeanFactory();
                if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
                        this.lifecycleProcessor =
                                        beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
                        if (logger.isTraceEnabled()) {
                                logger.trace("Using LifecycleProcessor [" + this.lifecycleProcessor + "]");
                        }
                }
                else {
                        DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
                        defaultProcessor.setBeanFactory(beanFactory);
                        this.lifecycleProcessor = defaultProcessor;
                        beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
                        if (logger.isTraceEnabled()) {
                                logger.trace("No '" + LIFECYCLE_PROCESSOR_BEAN_NAME + "' bean, using " +
                                                "[" + this.lifecycleProcessor.getClass().getSimpleName() + "]");
                        }
                }
        }

        /**
         * Template method which can be overridden to add context-specific refresh work.
         * Called on initialization of special beans, before instantiation of singletons.
         * <p>This implementation is empty.
         * @throws BeansException in case of errors
         * @see #refresh()
         */
        protected void onRefresh() throws BeansException {
                // For subclasses: do nothing by default.
        }

        /**
         * Add beans that implement ApplicationListener as listeners.
         * Doesn't affect other listeners, which can be added without being beans.
         */
        protected void registerListeners() {
                // Register statically specified listeners first.
                for (ApplicationListener<?> listener : getApplicationListeners()) {
                        getApplicationEventMulticaster().addApplicationListener(listener);
                }

                // Do not initialize FactoryBeans here: We need to leave all regular beans
                // uninitialized to let post-processors apply to them!
                String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
                for (String listenerBeanName : listenerBeanNames) {
                        getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
                }

                // Publish early application events now that we finally have a multicaster...
                Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
                this.earlyApplicationEvents = null;
                if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
                        for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
                                getApplicationEventMulticaster().multicastEvent(earlyEvent);
                        }
                }
        }

        /**
         * Finish the initialization of this context's bean factory,
         * initializing all remaining singleton beans.
         */
        protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
                // Initialize conversion service for this context.
                if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
                                beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
                        beanFactory.setConversionService(
                                        beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
                }

                // Register a default embedded value resolver if no bean post-processor
                // (such as a PropertyPlaceholderConfigurer bean) registered any before:
                // at this point, primarily for resolution in annotation attribute values.
                if (!beanFactory.hasEmbeddedValueResolver()) {
                        beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
                }

                // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
                String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
                for (String weaverAwareName : weaverAwareNames) {
                        getBean(weaverAwareName);
                }

                // Stop using the temporary ClassLoader for type matching.
                beanFactory.setTempClassLoader(null);

                // Allow for caching all bean definition metadata, not expecting further changes.
                beanFactory.freezeConfiguration();

                // Instantiate all remaining (non-lazy-init) singletons.
                beanFactory.preInstantiateSingletons();
        }

        /**
         * Finish the refresh of this context, invoking the LifecycleProcessor's
         * onRefresh() method and publishing the
         * {@link org.springframework.context.event.ContextRefreshedEvent}.
         */
        protected void finishRefresh() {
                // Clear context-level resource caches (such as ASM metadata from scanning).
                clearResourceCaches();

                // Initialize lifecycle processor for this context.
                initLifecycleProcessor();

                // Propagate refresh to lifecycle processor first.
                getLifecycleProcessor().onRefresh();

                // Publish the final event.
                publishEvent(new ContextRefreshedEvent(this));

                // Participate in LiveBeansView MBean, if active.
                LiveBeansView.registerApplicationContext(this);
        }

        /**
         * Cancel this context's refresh attempt, resetting the {@code active} flag
         * after an exception got thrown.
         * @param ex the exception that led to the cancellation
         */
        protected void cancelRefresh(BeansException ex) {
                this.active.set(false);
        }

        /**
         * Reset Spring's common reflection metadata caches, in particular the
         * {@link ReflectionUtils}, {@link AnnotationUtils}, {@link ResolvableType}
         * and {@link CachedIntrospectionResults} caches.
         * @since 4.2
         * @see ReflectionUtils#clearCache()
         * @see AnnotationUtils#clearCache()
         * @see ResolvableType#clearCache()
         * @see CachedIntrospectionResults#clearClassLoader(ClassLoader)
         */
        protected void resetCommonCaches() {
                ReflectionUtils.clearCache();
                AnnotationUtils.clearCache();
                ResolvableType.clearCache();
                CachedIntrospectionResults.clearClassLoader(getClassLoader());
        }


        /**
         * Register a shutdown hook {@linkplain Thread#getName() named}
         * {@code SpringContextShutdownHook} with the JVM runtime, closing this
         * context on JVM shutdown unless it has already been closed at that time.
         * <p>Delegates to {@code doClose()} for the actual closing procedure.
         * @see Runtime#addShutdownHook
         * @see ConfigurableApplicationContext#SHUTDOWN_HOOK_THREAD_NAME
         * @see #close()
         * @see #doClose()
         */
        @Override
        public void registerShutdownHook() {
                if (this.shutdownHook == null) {
                        // No shutdown hook registered yet.
                        this.shutdownHook = new Thread(SHUTDOWN_HOOK_THREAD_NAME) {
                                @Override
                                public void run() {
                                        synchronized (startupShutdownMonitor) {
                                                doClose();
                                        }
                                }
                        };
                        Runtime.getRuntime().addShutdownHook(this.shutdownHook);
                }
        }

        /**
         * Callback for destruction of this instance, originally attached
         * to a {@code DisposableBean} implementation (not anymore in 5.0).
         * <p>The {@link #close()} method is the native way to shut down
         * an ApplicationContext, which this method simply delegates to.
         * @deprecated as of Spring Framework 5.0, in favor of {@link #close()}
         */
        @Deprecated
        public void destroy() {
                close();
        }

        /**
         * Close this application context, destroying all beans in its bean factory.
         * <p>Delegates to {@code doClose()} for the actual closing procedure.
         * Also removes a JVM shutdown hook, if registered, as it's not needed anymore.
         * @see #doClose()
         * @see #registerShutdownHook()
         */
        @Override
        public void close() {
                synchronized (this.startupShutdownMonitor) {
                        doClose();
                        // If we registered a JVM shutdown hook, we don't need it anymore now:
                        // We've already explicitly closed the context.
                        if (this.shutdownHook != null) {
                                try {
                                        Runtime.getRuntime().removeShutdownHook(this.shutdownHook);
                                }
                                catch (IllegalStateException ex) {
                                        // ignore - VM is already shutting down
                                }
                        }
                }
        }

        /**
         * Actually performs context closing: publishes a ContextClosedEvent and
         * destroys the singletons in the bean factory of this application context.
         * <p>Called by both {@code close()} and a JVM shutdown hook, if any.
         * @see org.springframework.context.event.ContextClosedEvent
         * @see #destroyBeans()
         * @see #close()
         * @see #registerShutdownHook()
         */
        protected void doClose() {
                // Check whether an actual close attempt is necessary...
                if (this.active.get() && this.closed.compareAndSet(false, true)) {
                        if (logger.isDebugEnabled()) {
                                logger.debug("Closing " + this);
                        }

                        LiveBeansView.unregisterApplicationContext(this);

                        try {
                                // Publish shutdown event.
                                publishEvent(new ContextClosedEvent(this));
                        }
                        catch (Throwable ex) {
                                logger.warn("Exception thrown from ApplicationListener handling ContextClosedEvent", ex);
                        }

                        // Stop all Lifecycle beans, to avoid delays during individual destruction.
                        if (this.lifecycleProcessor != null) {
                                try {
                                        this.lifecycleProcessor.onClose();
                                }
                                catch (Throwable ex) {
                                        logger.warn("Exception thrown from LifecycleProcessor on context close", ex);
                                }
                        }

                        // Destroy all cached singletons in the context's BeanFactory.
                        destroyBeans();

                        // Close the state of this context itself.
                        closeBeanFactory();

                        // Let subclasses do some final clean-up if they wish...
                        onClose();

                        // Reset local application listeners to pre-refresh state.
                        if (this.earlyApplicationListeners != null) {
                                this.applicationListeners.clear();
                                this.applicationListeners.addAll(this.earlyApplicationListeners);
                        }

                        // Switch to inactive.
                        this.active.set(false);
                }
        }

        /**
         * Template method for destroying all beans that this context manages.
         * The default implementation destroy all cached singletons in this context,
         * invoking {@code DisposableBean.destroy()} and/or the specified
         * "destroy-method".
         * <p>Can be overridden to add context-specific bean destruction steps
         * right before or right after standard singleton destruction,
         * while the context's BeanFactory is still active.
         * @see #getBeanFactory()
         * @see org.springframework.beans.factory.config.ConfigurableBeanFactory#destroySingletons()
         */
        protected void destroyBeans() {
                getBeanFactory().destroySingletons();
        }

        /**
         * Template method which can be overridden to add context-specific shutdown work.
         * The default implementation is empty.
         * <p>Called at the end of {@link #doClose}'s shutdown procedure, after
         * this context's BeanFactory has been closed. If custom shutdown logic
         * needs to execute while the BeanFactory is still active, override
         * the {@link #destroyBeans()} method instead.
         */
        protected void onClose() {
                // For subclasses: do nothing by default.
        }

        @Override
        public boolean isActive() {
                return this.active.get();
        }

        /**
         * Assert that this context's BeanFactory is currently active,
         * throwing an {@link IllegalStateException} if it isn't.
         * <p>Invoked by all {@link BeanFactory} delegation methods that depend
         * on an active context, i.e. in particular all bean accessor methods.
         * <p>The default implementation checks the {@link #isActive() 'active'} status
         * of this context overall. May be overridden for more specific checks, or for a
         * no-op if {@link #getBeanFactory()} itself throws an exception in such a case.
         */
        protected void assertBeanFactoryActive() {
                if (!this.active.get()) {
                        if (this.closed.get()) {
                                throw new IllegalStateException(getDisplayName() + " has been closed already");
                        }
                        else {
                                throw new IllegalStateException(getDisplayName() + " has not been refreshed yet");
                        }
                }
        }


        //---------------------------------------------------------------------
        // Implementation of BeanFactory interface
        //---------------------------------------------------------------------

        @Override
        public Object getBean(String name) throws BeansException {
                assertBeanFactoryActive();
                return getBeanFactory().getBean(name);
        }

        @Override
        public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
                assertBeanFactoryActive();
                return getBeanFactory().getBean(name, requiredType);
        }

        @Override
        public Object getBean(String name, Object... args) throws BeansException {
                assertBeanFactoryActive();
                return getBeanFactory().getBean(name, args);
        }

        @Override
        public <T> T getBean(Class<T> requiredType) throws BeansException {
                assertBeanFactoryActive();
                return getBeanFactory().getBean(requiredType);
        }

        @Override
        public <T> T getBean(Class<T> requiredType, Object... args) throws BeansException {
                assertBeanFactoryActive();
                return getBeanFactory().getBean(requiredType, args);
        }

        @Override
        public <T> ObjectProvider<T> getBeanProvider(Class<T> requiredType) {
                assertBeanFactoryActive();
                return getBeanFactory().getBeanProvider(requiredType);
        }

        @Override
        public <T> ObjectProvider<T> getBeanProvider(ResolvableType requiredType) {
                assertBeanFactoryActive();
                return getBeanFactory().getBeanProvider(requiredType);
        }

        @Override
        public boolean containsBean(String name) {
                return getBeanFactory().containsBean(name);
        }

        @Override
        public boolean isSingleton(String name) throws NoSuchBeanDefinitionException {
                assertBeanFactoryActive();
                return getBeanFactory().isSingleton(name);
        }

        @Override
        public boolean isPrototype(String name) throws NoSuchBeanDefinitionException {
                assertBeanFactoryActive();
                return getBeanFactory().isPrototype(name);
        }

        @Override
        public boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException {
                assertBeanFactoryActive();
                return getBeanFactory().isTypeMatch(name, typeToMatch);
        }

        @Override
        public boolean isTypeMatch(String name, Class<?> typeToMatch) throws NoSuchBeanDefinitionException {
                assertBeanFactoryActive();
                return getBeanFactory().isTypeMatch(name, typeToMatch);
        }

        @Override
        @Nullable
        public Class<?> getType(String name) throws NoSuchBeanDefinitionException {
                assertBeanFactoryActive();
                return getBeanFactory().getType(name);
        }

        @Override
        @Nullable
        public Class<?> getType(String name, boolean allowFactoryBeanInit) throws NoSuchBeanDefinitionException {
                assertBeanFactoryActive();
                return getBeanFactory().getType(name, allowFactoryBeanInit);
        }

        @Override
        public String[] getAliases(String name) {
                return getBeanFactory().getAliases(name);
        }


        //---------------------------------------------------------------------
        // Implementation of ListableBeanFactory interface
        //---------------------------------------------------------------------

        @Override
        public boolean containsBeanDefinition(String beanName) {
                return getBeanFactory().containsBeanDefinition(beanName);
        }

        @Override
        public int getBeanDefinitionCount() {
                return getBeanFactory().getBeanDefinitionCount();
        }

        @Override
        public String[] getBeanDefinitionNames() {
                return getBeanFactory().getBeanDefinitionNames();
        }

        @Override
        public String[] getBeanNamesForType(ResolvableType type) {
                assertBeanFactoryActive();
                return getBeanFactory().getBeanNamesForType(type);
        }

        @Override
        public String[] getBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {
                assertBeanFactoryActive();
                return getBeanFactory().getBeanNamesForType(type, includeNonSingletons, allowEagerInit);
        }

        @Override
        public String[] getBeanNamesForType(@Nullable Class<?> type) {
                assertBeanFactoryActive();
                return getBeanFactory().getBeanNamesForType(type);
        }

        @Override
        public String[] getBeanNamesForType(@Nullable Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
                assertBeanFactoryActive();
                return getBeanFactory().getBeanNamesForType(type, includeNonSingletons, allowEagerInit);
        }

        @Override
        public <T> Map<String, T> getBeansOfType(@Nullable Class<T> type) throws BeansException {
                assertBeanFactoryActive();
                return getBeanFactory().getBeansOfType(type);
        }

        @Override
        public <T> Map<String, T> getBeansOfType(@Nullable Class<T> type, boolean includeNonSingletons, boolean allowEagerInit)
                        throws BeansException {

                assertBeanFactoryActive();
                return getBeanFactory().getBeansOfType(type, includeNonSingletons, allowEagerInit);
        }

        @Override
        public String[] getBeanNamesForAnnotation(Class<? extends Annotation> annotationType) {
                assertBeanFactoryActive();
                return getBeanFactory().getBeanNamesForAnnotation(annotationType);
        }

        @Override
        public Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType)
                        throws BeansException {

                assertBeanFactoryActive();
                return getBeanFactory().getBeansWithAnnotation(annotationType);
        }

        @Override
        @Nullable
        public <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType)
                        throws NoSuchBeanDefinitionException {

                assertBeanFactoryActive();
                return getBeanFactory().findAnnotationOnBean(beanName, annotationType);
        }


        //---------------------------------------------------------------------
        // Implementation of HierarchicalBeanFactory interface
        //---------------------------------------------------------------------

        @Override
        @Nullable
        public BeanFactory getParentBeanFactory() {
                return getParent();
        }

        @Override
        public boolean containsLocalBean(String name) {
                return getBeanFactory().containsLocalBean(name);
        }

        /**
         * Return the internal bean factory of the parent context if it implements
         * ConfigurableApplicationContext; else, return the parent context itself.
         * @see org.springframework.context.ConfigurableApplicationContext#getBeanFactory
         */
        @Nullable
        protected BeanFactory getInternalParentBeanFactory() {
                return (getParent() instanceof ConfigurableApplicationContext ?
                                ((ConfigurableApplicationContext) getParent()).getBeanFactory() : getParent());
        }


        //---------------------------------------------------------------------
        // Implementation of MessageSource interface
        //---------------------------------------------------------------------

        @Override
        public String getMessage(String code, @Nullable Object[] args, @Nullable String defaultMessage, Locale locale) {
                return getMessageSource().getMessage(code, args, defaultMessage, locale);
        }

        @Override
        public String getMessage(String code, @Nullable Object[] args, Locale locale) throws NoSuchMessageException {
                return getMessageSource().getMessage(code, args, locale);
        }

        @Override
        public String getMessage(MessageSourceResolvable resolvable, Locale locale) throws NoSuchMessageException {
                return getMessageSource().getMessage(resolvable, locale);
        }

        /**
         * Return the internal MessageSource used by the context.
         * @return the internal MessageSource (never {@code null})
         * @throws IllegalStateException if the context has not been initialized yet
         */
        private MessageSource getMessageSource() throws IllegalStateException {
                if (this.messageSource == null) {
                        throw new IllegalStateException("MessageSource not initialized - " +
                                        "call 'refresh' before accessing messages via the context: " + this);
                }
                return this.messageSource;
        }

        /**
         * Return the internal message source of the parent context if it is an
         * AbstractApplicationContext too; else, return the parent context itself.
         */
        @Nullable
        protected MessageSource getInternalParentMessageSource() {
                return (getParent() instanceof AbstractApplicationContext ?
                                ((AbstractApplicationContext) getParent()).messageSource : getParent());
        }


        //---------------------------------------------------------------------
        // Implementation of ResourcePatternResolver interface
        //---------------------------------------------------------------------

        @Override
        public Resource[] getResources(String locationPattern) throws IOException {
                return this.resourcePatternResolver.getResources(locationPattern);
        }


        //---------------------------------------------------------------------
        // Implementation of Lifecycle interface
        //---------------------------------------------------------------------

        @Override
        public void start() {
                getLifecycleProcessor().start();
                publishEvent(new ContextStartedEvent(this));
        }

        @Override
        public void stop() {
                getLifecycleProcessor().stop();
                publishEvent(new ContextStoppedEvent(this));
        }

        @Override
        public boolean isRunning() {
                return (this.lifecycleProcessor != null && this.lifecycleProcessor.isRunning());
        }


        //---------------------------------------------------------------------
        // Abstract methods that must be implemented by subclasses
        //---------------------------------------------------------------------

        /**
         * Subclasses must implement this method to perform the actual configuration load.
         * The method is invoked by {@link #refresh()} before any other initialization work.
         * <p>A subclass will either create a new bean factory and hold a reference to it,
         * or return a single BeanFactory instance that it holds. In the latter case, it will
         * usually throw an IllegalStateException if refreshing the context more than once.
         * @throws BeansException if initialization of the bean factory failed
         * @throws IllegalStateException if already initialized and multiple refresh
         * attempts are not supported
         */
        protected abstract void refreshBeanFactory() throws BeansException, IllegalStateException;

        /**
         * Subclasses must implement this method to release their internal bean factory.
         * This method gets invoked by {@link #close()} after all other shutdown work.
         * <p>Should never throw an exception but rather log shutdown failures.
         */
        protected abstract void closeBeanFactory();

        /**
         * Subclasses must return their internal bean factory here. They should implement the
         * lookup efficiently, so that it can be called repeatedly without a performance penalty.
         * <p>Note: Subclasses should check whether the context is still active before
         * returning the internal bean factory. The internal factory should generally be
         * considered unavailable once the context has been closed.
         * @return this application context's internal bean factory (never {@code null})
         * @throws IllegalStateException if the context does not hold an internal bean factory yet
         * (usually if {@link #refresh()} has never been called) or if the context has been
         * closed already
         * @see #refreshBeanFactory()
         * @see #closeBeanFactory()
         */
        @Override
        public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;


        /**
         * Return information about this context.
         */
        @Override
        public String toString() {
                StringBuilder sb = new StringBuilder(getDisplayName());
                sb.append(", started on ").append(new Date(getStartupDate()));
                ApplicationContext parent = getParent();
                if (parent != null) {
                        sb.append(", parent: ").append(parent.getDisplayName());
                }
                return sb.toString();
        }

}