org.springframework/spring-web/5.3.3 : org/springframework/web/context/ContextLoader.java

ContextLoader
https://github.com/spring-projects/spring-framework: Spring Web (Spring IO)
Apache License, Version 2.0
Juergen Hoeller
/*
 * Copyright 2002-2018 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.web.context;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.ConcurrentHashMap;

import javax.servlet.ServletContext;

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

import org.springframework.beans.BeanUtils;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextException;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.GenericTypeResolver;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.support.PropertiesLoaderUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.util.StringUtils;

Performs the actual initialization work for the root application context. Called by ContextLoaderListener. Looks for a "contextClass" parameter at the web.xml context-param level to specify the context class type, falling back to XmlWebApplicationContext if not found. With the default ContextLoader implementation, any context class specified needs to implement the ConfigurableWebApplicationContext interface. 
Processes a "contextConfigLocation" context-param and passes its value to the context instance, parsing it into potentially multiple file paths which can be separated by any number of commas and spaces, e.g. "WEB-INF/applicationContext1.xml, WEB-INF/applicationContext2.xml". Ant-style path patterns are supported as well, e.g. "WEB-INF/*Context.xml,WEB-INF/spring*.xml" or "WEB-INF/**/*Context.xml". If not explicitly specified, the context implementation is supposed to use a default location (with XmlWebApplicationContext: "/WEB-INF/applicationContext.xml"). 
Note: In case of multiple config locations, later bean definitions will
override ones defined in previously loaded files, at least when using one of
Spring's default ApplicationContext implementations. This can be leveraged
to deliberately override certain bean definitions via an extra XML file.
Above and beyond loading the root application context, this class can optionally load or obtain and hook up a shared parent context to the root application context. See the loadParentContext(ServletContext) method for more information. 
As of Spring 3.1, ContextLoader supports injecting the root web application context via the ContextLoader(WebApplicationContext) constructor, allowing for programmatic configuration in Servlet 3.0+ environments. See WebApplicationInitializer for usage examples. 
Author: Juergen Hoeller, Colin Sampaleanu, Sam Brannen
See Also: ContextLoaderListener
ConfigurableWebApplicationContext
XmlWebApplicationContext
Since: 17.02.2003/**
 * Performs the actual initialization work for the root application context.
 * Called by {@link ContextLoaderListener}.
 *
 * <p>Looks for a {@link #CONTEXT_CLASS_PARAM "contextClass"} parameter at the
 * {@code web.xml} context-param level to specify the context class type, falling
 * back to {@link org.springframework.web.context.support.XmlWebApplicationContext}
 * if not found. With the default ContextLoader implementation, any context class
 * specified needs to implement the {@link ConfigurableWebApplicationContext} interface.
 *
 * <p>Processes a {@link #CONFIG_LOCATION_PARAM "contextConfigLocation"} context-param
 * and passes its value to the context instance, parsing it into potentially multiple
 * file paths which can be separated by any number of commas and spaces, e.g.
 * "WEB-INF/applicationContext1.xml, WEB-INF/applicationContext2.xml".
 * Ant-style path patterns are supported as well, e.g.
 * "WEB-INF/*Context.xml,WEB-INF/spring*.xml" or "WEB-INF/&#42;&#42;/*Context.xml".
 * If not explicitly specified, the context implementation is supposed to use a
 * default location (with XmlWebApplicationContext: "/WEB-INF/applicationContext.xml").
 *
 * <p>Note: In case of multiple config locations, later bean definitions will
 * override ones defined in previously loaded files, at least when using one of
 * Spring's default ApplicationContext implementations. This can be leveraged
 * to deliberately override certain bean definitions via an extra XML file.
 *
 * <p>Above and beyond loading the root application context, this class can optionally
 * load or obtain and hook up a shared parent context to the root application context.
 * See the {@link #loadParentContext(ServletContext)} method for more information.
 *
 * <p>As of Spring 3.1, {@code ContextLoader} supports injecting the root web
 * application context via the {@link #ContextLoader(WebApplicationContext)}
 * constructor, allowing for programmatic configuration in Servlet 3.0+ environments.
 * See {@link org.springframework.web.WebApplicationInitializer} for usage examples.
 *
 * @author Juergen Hoeller
 * @author Colin Sampaleanu
 * @author Sam Brannen
 * @since 17.02.2003
 * @see ContextLoaderListener
 * @see ConfigurableWebApplicationContext
 * @see org.springframework.web.context.support.XmlWebApplicationContext
 */
public class ContextLoader {

	Config param for the root WebApplicationContext id, to be used as serialization id for the underlying BeanFactory: "contextId". /**
	 * Config param for the root WebApplicationContext id,
	 * to be used as serialization id for the underlying BeanFactory: {@value}.
	 */
	public static final String CONTEXT_ID_PARAM = "contextId";

	Name of servlet context parameter (i.e., "contextConfigLocation") that can specify the config location for the root context, falling back to the implementation's default otherwise. 
See Also: XmlWebApplicationContext.DEFAULT_CONFIG_LOCATION/**
	 * Name of servlet context parameter (i.e., {@value}) that can specify the
	 * config location for the root context, falling back to the implementation's
	 * default otherwise.
	 * @see org.springframework.web.context.support.XmlWebApplicationContext#DEFAULT_CONFIG_LOCATION
	 */
	public static final String CONFIG_LOCATION_PARAM = "contextConfigLocation";

	Config param for the root WebApplicationContext implementation class to use: "contextClass". 
See Also: determineContextClass(ServletContext)/**
	 * Config param for the root WebApplicationContext implementation class to use: {@value}.
	 * @see #determineContextClass(ServletContext)
	 */
	public static final String CONTEXT_CLASS_PARAM = "contextClass";

	Config param for ApplicationContextInitializer classes to use for initializing the root web application context: "contextInitializerClasses". 
See Also: customizeContext(ServletContext, ConfigurableWebApplicationContext)/**
	 * Config param for {@link ApplicationContextInitializer} classes to use
	 * for initializing the root web application context: {@value}.
	 * @see #customizeContext(ServletContext, ConfigurableWebApplicationContext)
	 */
	public static final String CONTEXT_INITIALIZER_CLASSES_PARAM = "contextInitializerClasses";

	Config param for global ApplicationContextInitializer classes to use for initializing all web application contexts in the current application: "globalInitializerClasses". 
See Also: customizeContext(ServletContext, ConfigurableWebApplicationContext)/**
	 * Config param for global {@link ApplicationContextInitializer} classes to use
	 * for initializing all web application contexts in the current application: {@value}.
	 * @see #customizeContext(ServletContext, ConfigurableWebApplicationContext)
	 */
	public static final String GLOBAL_INITIALIZER_CLASSES_PARAM = "globalInitializerClasses";

	Any number of these characters are considered delimiters between
multiple values in a single init-param String value.
/**
	 * Any number of these characters are considered delimiters between
	 * multiple values in a single init-param String value.
	 */
	private static final String INIT_PARAM_DELIMITERS = ",; \t\n";

	Name of the class path resource (relative to the ContextLoader class)
that defines ContextLoader's default strategy names.
/**
	 * Name of the class path resource (relative to the ContextLoader class)
	 * that defines ContextLoader's default strategy names.
	 */
	private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";


	private static final Properties defaultStrategies;

	static {
		// Load default strategy implementations from properties file.
		// This is currently strictly internal and not meant to be customized
		// by application developers.
		try {
			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
		}
	}


	Map from (thread context) ClassLoader to corresponding 'current' WebApplicationContext.
/**
	 * Map from (thread context) ClassLoader to corresponding 'current' WebApplicationContext.
	 */
	private static final Map<ClassLoader, WebApplicationContext> currentContextPerThread =
			new ConcurrentHashMap<>(1);

	The 'current' WebApplicationContext, if the ContextLoader class is
deployed in the web app ClassLoader itself.
/**
	 * The 'current' WebApplicationContext, if the ContextLoader class is
	 * deployed in the web app ClassLoader itself.
	 */
	@Nullable
	private static volatile WebApplicationContext currentContext;


	The root WebApplicationContext instance that this loader manages.
/**
	 * The root WebApplicationContext instance that this loader manages.
	 */
	@Nullable
	private WebApplicationContext context;

	Actual ApplicationContextInitializer instances to apply to the context. /** Actual ApplicationContextInitializer instances to apply to the context. */
	private final List<ApplicationContextInitializer<ConfigurableApplicationContext>> contextInitializers =
			new ArrayList<>();


	Create a new ContextLoader that will create a web application context based on the "contextClass" and "contextConfigLocation" servlet context-params. See class-level documentation for details on default values for each. This constructor is typically used when declaring the 
ContextLoaderListener subclass as a <listener> within web.xml, as a no-arg constructor is required. 
The created application context will be registered into the ServletContext under the attribute name WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE and subclasses are free to call the closeWebApplicationContext method on container shutdown to close the application context. 
See Also: ContextLoader(WebApplicationContext)
initWebApplicationContext(ServletContext)
closeWebApplicationContext(ServletContext)/**
	 * Create a new {@code ContextLoader} that will create a web application context
	 * based on the "contextClass" and "contextConfigLocation" servlet context-params.
	 * See class-level documentation for details on default values for each.
	 * <p>This constructor is typically used when declaring the {@code
	 * ContextLoaderListener} subclass as a {@code <listener>} within {@code web.xml}, as
	 * a no-arg constructor is required.
	 * <p>The created application context will be registered into the ServletContext under
	 * the attribute name {@link WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE}
	 * and subclasses are free to call the {@link #closeWebApplicationContext} method on
	 * container shutdown to close the application context.
	 * @see #ContextLoader(WebApplicationContext)
	 * @see #initWebApplicationContext(ServletContext)
	 * @see #closeWebApplicationContext(ServletContext)
	 */
	public ContextLoader() {
	}

	Create a new ContextLoader with the given application context. This constructor is useful in Servlet 3.0+ environments where instance-based registration of listeners is possible through the addListener.addListener API. The context may or may not yet be refreshed. If it (a) is an implementation of ConfigurableWebApplicationContext and (b) has not
already been refreshed (the recommended approach), then the following will occur:

If the given context has not already been assigned an id, one will be assigned to it
ServletContext and ServletConfig objects will be delegated to the application context
customizeContext will be called
Any ApplicationContextInitializers specified through the "contextInitializerClasses" init-param will be applied.
refresh() will be called
 If the context has already been refreshed or does not implement ConfigurableWebApplicationContext, none of the above will occur under the assumption that the user has performed these actions (or not) per his or her specific needs. See WebApplicationInitializer for usage examples. 
In any case, the given application context will be registered into the ServletContext under the attribute name WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE and subclasses are free to call the closeWebApplicationContext method on container shutdown to close the application context. 
Params: context – the application context to manage
See Also: initWebApplicationContext(ServletContext)
closeWebApplicationContext(ServletContext)/**
	 * Create a new {@code ContextLoader} with the given application context. This
	 * constructor is useful in Servlet 3.0+ environments where instance-based
	 * registration of listeners is possible through the {@link ServletContext#addListener}
	 * API.
	 * <p>The context may or may not yet be {@linkplain
	 * ConfigurableApplicationContext#refresh() refreshed}. If it (a) is an implementation
	 * of {@link ConfigurableWebApplicationContext} and (b) has <strong>not</strong>
	 * already been refreshed (the recommended approach), then the following will occur:
	 * <ul>
	 * <li>If the given context has not already been assigned an {@linkplain
	 * ConfigurableApplicationContext#setId id}, one will be assigned to it</li>
	 * <li>{@code ServletContext} and {@code ServletConfig} objects will be delegated to
	 * the application context</li>
	 * <li>{@link #customizeContext} will be called</li>
	 * <li>Any {@link ApplicationContextInitializer ApplicationContextInitializers} specified through the
	 * "contextInitializerClasses" init-param will be applied.</li>
	 * <li>{@link ConfigurableApplicationContext#refresh refresh()} will be called</li>
	 * </ul>
	 * If the context has already been refreshed or does not implement
	 * {@code ConfigurableWebApplicationContext}, none of the above will occur under the
	 * assumption that the user has performed these actions (or not) per his or her
	 * specific needs.
	 * <p>See {@link org.springframework.web.WebApplicationInitializer} for usage examples.
	 * <p>In any case, the given application context will be registered into the
	 * ServletContext under the attribute name {@link
	 * WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE} and subclasses are
	 * free to call the {@link #closeWebApplicationContext} method on container shutdown
	 * to close the application context.
	 * @param context the application context to manage
	 * @see #initWebApplicationContext(ServletContext)
	 * @see #closeWebApplicationContext(ServletContext)
	 */
	public ContextLoader(WebApplicationContext context) {
		this.context = context;
	}


	Specify which ApplicationContextInitializer instances should be used to initialize the application context used by this ContextLoader. 
See Also: configureAndRefreshWebApplicationContext
customizeContext
Since: 4.2/**
	 * Specify which {@link ApplicationContextInitializer} instances should be used
	 * to initialize the application context used by this {@code ContextLoader}.
	 * @since 4.2
	 * @see #configureAndRefreshWebApplicationContext
	 * @see #customizeContext
	 */
	@SuppressWarnings("unchecked")
	public void setContextInitializers(@Nullable ApplicationContextInitializer<?>... initializers) {
		if (initializers != null) {
			for (ApplicationContextInitializer<?> initializer : initializers) {
				this.contextInitializers.add((ApplicationContextInitializer<ConfigurableApplicationContext>) initializer);
			}
		}
	}


	Initialize Spring's web application context for the given servlet context, using the application context provided at construction time, or creating a new one according to the "contextClass" and "contextConfigLocation" context-params. 
Params: servletContext – current servlet context
See Also: ContextLoader(WebApplicationContext)
CONTEXT_CLASS_PARAM
CONFIG_LOCATION_PARAM
Returns: the new WebApplicationContext/**
	 * Initialize Spring's web application context for the given servlet context,
	 * using the application context provided at construction time, or creating a new one
	 * according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and
	 * "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params.
	 * @param servletContext current servlet context
	 * @return the new WebApplicationContext
	 * @see #ContextLoader(WebApplicationContext)
	 * @see #CONTEXT_CLASS_PARAM
	 * @see #CONFIG_LOCATION_PARAM
	 */
	public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
		if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
			throw new IllegalStateException(
					"Cannot initialize context because there is already a root application context present - " +
					"check whether you have multiple ContextLoader* definitions in your web.xml!");
		}

		servletContext.log("Initializing Spring root WebApplicationContext");
		Log logger = LogFactory.getLog(ContextLoader.class);
		if (logger.isInfoEnabled()) {
			logger.info("Root WebApplicationContext: initialization started");
		}
		long startTime = System.currentTimeMillis();

		try {
			// Store context in local instance variable, to guarantee that
			// it is available on ServletContext shutdown.
			if (this.context == null) {
				this.context = createWebApplicationContext(servletContext);
			}
			if (this.context instanceof ConfigurableWebApplicationContext) {
				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
				if (!cwac.isActive()) {
					// The context has not yet been refreshed -> provide services such as
					// setting the parent context, setting the application context id, etc
					if (cwac.getParent() == null) {
						// The context instance was injected without an explicit parent ->
						// determine parent for root web application context, if any.
						ApplicationContext parent = loadParentContext(servletContext);
						cwac.setParent(parent);
					}
					configureAndRefreshWebApplicationContext(cwac, servletContext);
				}
			}
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

			ClassLoader ccl = Thread.currentThread().getContextClassLoader();
			if (ccl == ContextLoader.class.getClassLoader()) {
				currentContext = this.context;
			}
			else if (ccl != null) {
				currentContextPerThread.put(ccl, this.context);
			}

			if (logger.isInfoEnabled()) {
				long elapsedTime = System.currentTimeMillis() - startTime;
				logger.info("Root WebApplicationContext initialized in " + elapsedTime + " ms");
			}

			return this.context;
		}
		catch (RuntimeException | Error ex) {
			logger.error("Context initialization failed", ex);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
			throw ex;
		}
	}

	Instantiate the root WebApplicationContext for this loader, either the
default context class or a custom context class if specified.
This implementation expects custom contexts to implement the ConfigurableWebApplicationContext interface. Can be overridden in subclasses. 
In addition, customizeContext gets called prior to refreshing the context, allowing subclasses to perform custom modifications to the context. 
Params: sc – current servlet context
See Also: ConfigurableWebApplicationContext
Returns: the root WebApplicationContext/**
	 * Instantiate the root WebApplicationContext for this loader, either the
	 * default context class or a custom context class if specified.
	 * <p>This implementation expects custom contexts to implement the
	 * {@link ConfigurableWebApplicationContext} interface.
	 * Can be overridden in subclasses.
	 * <p>In addition, {@link #customizeContext} gets called prior to refreshing the
	 * context, allowing subclasses to perform custom modifications to the context.
	 * @param sc current servlet context
	 * @return the root WebApplicationContext
	 * @see ConfigurableWebApplicationContext
	 */
	protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
		Class<?> contextClass = determineContextClass(sc);
		if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
			throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
					"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
		}
		return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
	}

	Return the WebApplicationContext implementation class to use, either the
default XmlWebApplicationContext or a custom context class if specified.
Params: servletContext – current servlet context
See Also: CONTEXT_CLASS_PARAM
XmlWebApplicationContext
Returns: the WebApplicationContext implementation class to use/**
	 * Return the WebApplicationContext implementation class to use, either the
	 * default XmlWebApplicationContext or a custom context class if specified.
	 * @param servletContext current servlet context
	 * @return the WebApplicationContext implementation class to use
	 * @see #CONTEXT_CLASS_PARAM
	 * @see org.springframework.web.context.support.XmlWebApplicationContext
	 */
	protected Class<?> determineContextClass(ServletContext servletContext) {
		String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
		if (contextClassName != null) {
			try {
				return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
			}
			catch (ClassNotFoundException ex) {
				throw new ApplicationContextException(
						"Failed to load custom context class [" + contextClassName + "]", ex);
			}
		}
		else {
			contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
			try {
				return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
			}
			catch (ClassNotFoundException ex) {
				throw new ApplicationContextException(
						"Failed to load default context class [" + contextClassName + "]", ex);
			}
		}
	}

	protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
		if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
			// The application context id is still set to its original default value
			// -> assign a more useful id based on available information
			String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
			if (idParam != null) {
				wac.setId(idParam);
			}
			else {
				// Generate default id...
				wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
						ObjectUtils.getDisplayString(sc.getContextPath()));
			}
		}

		wac.setServletContext(sc);
		String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
		if (configLocationParam != null) {
			wac.setConfigLocation(configLocationParam);
		}

		// The wac environment's #initPropertySources will be called in any case when the context
		// is refreshed; do it eagerly here to ensure servlet property sources are in place for
		// use in any post-processing or initialization that occurs below prior to #refresh
		ConfigurableEnvironment env = wac.getEnvironment();
		if (env instanceof ConfigurableWebEnvironment) {
			((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
		}

		customizeContext(sc, wac);
		wac.refresh();
	}

	Customize the ConfigurableWebApplicationContext created by this ContextLoader after config locations have been supplied to the context but before the context is refreshed.
The default implementation 
determines what (if any) context initializer classes have been specified through context init parameters and invokes each with the given web application context. 
Any ApplicationContextInitializers implementing Ordered or marked with @Order will be sorted appropriately. 
Params: sc – the current servlet context
wac – the newly created application context
See Also: CONTEXT_INITIALIZER_CLASSES_PARAM
initialize.initialize(ConfigurableApplicationContext)/**
	 * Customize the {@link ConfigurableWebApplicationContext} created by this
	 * ContextLoader after config locations have been supplied to the context
	 * but before the context is <em>refreshed</em>.
	 * <p>The default implementation {@linkplain #determineContextInitializerClasses(ServletContext)
	 * determines} what (if any) context initializer classes have been specified through
	 * {@linkplain #CONTEXT_INITIALIZER_CLASSES_PARAM context init parameters} and
	 * {@linkplain ApplicationContextInitializer#initialize invokes each} with the
	 * given web application context.
	 * <p>Any {@code ApplicationContextInitializers} implementing
	 * {@link org.springframework.core.Ordered Ordered} or marked with @{@link
	 * org.springframework.core.annotation.Order Order} will be sorted appropriately.
	 * @param sc the current servlet context
	 * @param wac the newly created application context
	 * @see #CONTEXT_INITIALIZER_CLASSES_PARAM
	 * @see ApplicationContextInitializer#initialize(ConfigurableApplicationContext)
	 */
	protected void customizeContext(ServletContext sc, ConfigurableWebApplicationContext wac) {
		List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> initializerClasses =
				determineContextInitializerClasses(sc);

		for (Class<ApplicationContextInitializer<ConfigurableApplicationContext>> initializerClass : initializerClasses) {
			Class<?> initializerContextClass =
					GenericTypeResolver.resolveTypeArgument(initializerClass, ApplicationContextInitializer.class);
			if (initializerContextClass != null && !initializerContextClass.isInstance(wac)) {
				throw new ApplicationContextException(String.format(
						"Could not apply context initializer [%s] since its generic parameter [%s] " +
						"is not assignable from the type of application context used by this " +
						"context loader: [%s]", initializerClass.getName(), initializerContextClass.getName(),
						wac.getClass().getName()));
			}
			this.contextInitializers.add(BeanUtils.instantiateClass(initializerClass));
		}

		AnnotationAwareOrderComparator.sort(this.contextInitializers);
		for (ApplicationContextInitializer<ConfigurableApplicationContext> initializer : this.contextInitializers) {
			initializer.initialize(wac);
		}
	}

	Return the ApplicationContextInitializer implementation classes to use if any have been specified by CONTEXT_INITIALIZER_CLASSES_PARAM. 
Params: servletContext – current servlet context
See Also: CONTEXT_INITIALIZER_CLASSES_PARAM/**
	 * Return the {@link ApplicationContextInitializer} implementation classes to use
	 * if any have been specified by {@link #CONTEXT_INITIALIZER_CLASSES_PARAM}.
	 * @param servletContext current servlet context
	 * @see #CONTEXT_INITIALIZER_CLASSES_PARAM
	 */
	protected List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>
			determineContextInitializerClasses(ServletContext servletContext) {

		List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> classes =
				new ArrayList<>();

		String globalClassNames = servletContext.getInitParameter(GLOBAL_INITIALIZER_CLASSES_PARAM);
		if (globalClassNames != null) {
			for (String className : StringUtils.tokenizeToStringArray(globalClassNames, INIT_PARAM_DELIMITERS)) {
				classes.add(loadInitializerClass(className));
			}
		}

		String localClassNames = servletContext.getInitParameter(CONTEXT_INITIALIZER_CLASSES_PARAM);
		if (localClassNames != null) {
			for (String className : StringUtils.tokenizeToStringArray(localClassNames, INIT_PARAM_DELIMITERS)) {
				classes.add(loadInitializerClass(className));
			}
		}

		return classes;
	}

	@SuppressWarnings("unchecked")
	private Class<ApplicationContextInitializer<ConfigurableApplicationContext>> loadInitializerClass(String className) {
		try {
			Class<?> clazz = ClassUtils.forName(className, ClassUtils.getDefaultClassLoader());
			if (!ApplicationContextInitializer.class.isAssignableFrom(clazz)) {
				throw new ApplicationContextException(
						"Initializer class does not implement ApplicationContextInitializer interface: " + clazz);
			}
			return (Class<ApplicationContextInitializer<ConfigurableApplicationContext>>) clazz;
		}
		catch (ClassNotFoundException ex) {
			throw new ApplicationContextException("Failed to load context initializer class [" + className + "]", ex);
		}
	}

	Template method with default implementation (which may be overridden by a
subclass), to load or obtain an ApplicationContext instance which will be
used as the parent context of the root WebApplicationContext. If the
return value from the method is null, no parent context is set.
The main reason to load a parent context here is to allow multiple root
web application contexts to all be children of a shared EAR context, or
alternately to also share the same parent context that is visible to
EJBs. For pure web applications, there is usually no need to worry about
having a parent context to the root web application context.
The default implementation simply returns null, as of 5.0. 
Params: servletContext – current servlet context
Returns: the parent application context, or null if none/**
	 * Template method with default implementation (which may be overridden by a
	 * subclass), to load or obtain an ApplicationContext instance which will be
	 * used as the parent context of the root WebApplicationContext. If the
	 * return value from the method is null, no parent context is set.
	 * <p>The main reason to load a parent context here is to allow multiple root
	 * web application contexts to all be children of a shared EAR context, or
	 * alternately to also share the same parent context that is visible to
	 * EJBs. For pure web applications, there is usually no need to worry about
	 * having a parent context to the root web application context.
	 * <p>The default implementation simply returns {@code null}, as of 5.0.
	 * @param servletContext current servlet context
	 * @return the parent application context, or {@code null} if none
	 */
	@Nullable
	protected ApplicationContext loadParentContext(ServletContext servletContext) {
		return null;
	}

	Close Spring's web application context for the given servlet context.
If overriding loadParentContext(ServletContext), you may have to override this method as well. 
Params: servletContext – the ServletContext that the WebApplicationContext runs in/**
	 * Close Spring's web application context for the given servlet context.
	 * <p>If overriding {@link #loadParentContext(ServletContext)}, you may have
	 * to override this method as well.
	 * @param servletContext the ServletContext that the WebApplicationContext runs in
	 */
	public void closeWebApplicationContext(ServletContext servletContext) {
		servletContext.log("Closing Spring root WebApplicationContext");
		try {
			if (this.context instanceof ConfigurableWebApplicationContext) {
				((ConfigurableWebApplicationContext) this.context).close();
			}
		}
		finally {
			ClassLoader ccl = Thread.currentThread().getContextClassLoader();
			if (ccl == ContextLoader.class.getClassLoader()) {
				currentContext = null;
			}
			else if (ccl != null) {
				currentContextPerThread.remove(ccl);
			}
			servletContext.removeAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
		}
	}


	Obtain the Spring root web application context for the current thread
(i.e. for the current thread's context ClassLoader, which needs to be
the web application's ClassLoader).
See Also: SpringBeanAutowiringSupport
Returns: the current root web application context, or null if none found/**
	 * Obtain the Spring root web application context for the current thread
	 * (i.e. for the current thread's context ClassLoader, which needs to be
	 * the web application's ClassLoader).
	 * @return the current root web application context, or {@code null}
	 * if none found
	 * @see org.springframework.web.context.support.SpringBeanAutowiringSupport
	 */
	@Nullable
	public static WebApplicationContext getCurrentWebApplicationContext() {
		ClassLoader ccl = Thread.currentThread().getContextClassLoader();
		if (ccl != null) {
			WebApplicationContext ccpt = currentContextPerThread.get(ccl);
			if (ccpt != null) {
				return ccpt;
			}
		}
		return currentContext;
	}

}
Author:	Juergen Hoeller, Colin Sampaleanu, Sam Brannen
See Also:	ContextLoaderListener ConfigurableWebApplicationContext XmlWebApplicationContext
Since:	17.02.2003
Params:	context – the application context to manage
See Also:	initWebApplicationContext(ServletContext) closeWebApplicationContext(ServletContext)
See Also:	configureAndRefreshWebApplicationContext customizeContext
Since:	4.2
Params:	servletContext – current servlet context
See Also:	ContextLoader(WebApplicationContext) CONTEXT_CLASS_PARAM CONFIG_LOCATION_PARAM
Returns:	the new WebApplicationContext
Params:	sc – current servlet context
See Also:	ConfigurableWebApplicationContext
Returns:	the root WebApplicationContext
Params:	sc – the current servlet context wac – the newly created application context
See Also:	CONTEXT_INITIALIZER_CLASSES_PARAM initialize.initialize(ConfigurableApplicationContext)
See Also:	SpringBeanAutowiringSupport
Returns:	the current root web application context, or `null` if none found
/

org.springframework/ spring-web/ 5.3.3/ org/springframework/web/context/ContextLoader.java
