spring--contextLoader源码

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 * Copyright 2002-2015 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
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
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 * Unless required by applicable law or agreed to in writing, software
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 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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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.beans.factory.access.BeanFactoryLocator;
import org.springframework.beans.factory.access.BeanFactoryReference;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextException;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.access.ContextSingletonBeanFactoryLocator;
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.util.Assert;
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 {@link ContextLoaderListener}.
 * 
 * 被ContextLoaderListener调用真正执行root application context初始化工作的地方
 *
 * 

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 the default of * {@link org.springframework.web.context.support.XmlWebApplicationContext} * if not found. With the default ContextLoader implementation, any context class * specified needs to implement the ConfigurableWebApplicationContext interface. * * 在web.xml文件的context-param标签中寻找contextClass参数,这个参数指定了上下文的类型, * 如果没有定义这个参数就使用默认的类型(XmlWebApplicationContext),任何被指定的上下文类 * 必须实现ConfigurableWebApplicationContext接口 * *

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/**/*Context.xml". * If not explicitly specified, the context implementation is supposed to use a * default location (with XmlWebApplicationContext: "/WEB-INF/applicationContext.xml"). * * web.xml中contextConfigLocation参数定义了配置文件的地址,通过这个参数去实例化上下文实例,该参数 * 可以配置多个值用空格和逗号分开,还支持ant风格的配置形式,支持使用通配符,如果没有定义该参数 * 默认地址(/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. * * 万一配置了多个配置文件地址,至少在使用spring默认的ApplicationContext的时候, * 如果有相同名字的bean的定义,较后加载的bean的定义将会覆盖较早加载的bean的定义 * *

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. * *

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: {@value} */ public static final String CONTEXT_ID_PARAM = "contextId"; /** * 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: {@value} * @see #determineContextClass(ServletContext) */ public static final String CONTEXT_CLASS_PARAM = "contextClass"; /** * 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 {@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"; /** * Optional servlet context parameter (i.e., "{@code locatorFactorySelector}") * used only when obtaining a parent context using the default implementation * of {@link #loadParentContext(ServletContext servletContext)}. * Specifies the 'selector' used in the * {@link ContextSingletonBeanFactoryLocator#getInstance(String selector)} * method call, which is used to obtain the BeanFactoryLocator instance from * which the parent context is obtained. *

The default is {@code classpath*:beanRefContext.xml}, * matching the default applied for the * {@link ContextSingletonBeanFactoryLocator#getInstance()} method. * Supplying the "parentContextKey" parameter is sufficient in this case. */ public static final String LOCATOR_FACTORY_SELECTOR_PARAM = "locatorFactorySelector"; /** * Optional servlet context parameter (i.e., "{@code parentContextKey}") * used only when obtaining a parent context using the default implementation * of {@link #loadParentContext(ServletContext servletContext)}. * Specifies the 'factoryKey' used in the * {@link BeanFactoryLocator#useBeanFactory(String factoryKey)} method call, * obtaining the parent application context from the BeanFactoryLocator instance. *

Supplying this "parentContextKey" parameter is sufficient when relying * on the default {@code classpath*:beanRefContext.xml} selector for * candidate factory references. */ public static final String LOCATOR_FACTORY_KEY_PARAM = "parentContextKey"; /** * 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. */ 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. */ private static final Map currentContextPerThread = new ConcurrentHashMap(1); /** * The 'current' WebApplicationContext, if the ContextLoader class is * deployed in the web app ClassLoader itself. */ private static volatile WebApplicationContext currentContext; /** * The root WebApplicationContext instance that this loader manages. */ private WebApplicationContext context; /** * Holds BeanFactoryReference when loading parent factory via * ContextSingletonBeanFactoryLocator. */ private BeanFactoryReference parentContextRef; /** Actual ApplicationContextInitializer instances to apply to the context */ private final List> contextInitializers = new ArrayList>(); /** * 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. *

This constructor is typically used when declaring the {@code * ContextLoaderListener} subclass as a {@code } within {@code web.xml}, as * a no-arg constructor is required. *

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 {@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. *

The context may or may not yet be {@linkplain * ConfigurableApplicationContext#refresh() refreshed}. If it (a) is an implementation * of {@link 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 {@linkplain * ConfigurableApplicationContext#setId id}, one will be assigned to it
  • *
  • {@code ServletContext} and {@code ServletConfig} objects will be delegated to * the application context
  • *
  • {@link #customizeContext} will be called
  • *
  • Any {@link ApplicationContextInitializer}s specified through the * "contextInitializerClasses" init-param will be applied.
  • *
  • {@link ConfigurableApplicationContext#refresh refresh()} will be called
  • *
* 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. *

See {@link org.springframework.web.WebApplicationInitializer} for usage examples. *

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 {@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(ApplicationContextInitializer... initializers) { if (initializers != null) { for (ApplicationContextInitializer initializer : initializers) { this.contextInitializers.add((ApplicationContextInitializer) 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 "{@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!"); } Log logger = LogFactory.getLog(ContextLoader.class); servletContext.log("Initializing Spring root WebApplicationContext"); 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) { //根据配置创建WebApplicationContext 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); } //初始化webApplicationContext configureAndRefreshWebApplicationContext(cwac, servletContext); } } //将webApplicationContext保存在servletContext中 servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context); // 获取线程上下文类加载器,默认为WebAppClassLoader ClassLoader ccl = Thread.currentThread().getContextClassLoader(); // 如果spring的jar包放在每个webapp自己的目录中 // 此时线程上下文类加载器会与本类的类加载器(加载spring的)相同,都是WebAppClassLoader if (ccl == ContextLoader.class.getClassLoader()) { currentContext = this.context; } else if (ccl != null) { // 如果不同,也就是上面说的那个问题的情况,那么用一个map把刚才创建的WebApplicationContext及对应的WebAppClassLoader存下来 // 一个webapp对应一个记录,后续调用时直接根据WebAppClassLoader来取出 currentContextPerThread.put(ccl, this.context); } if (logger.isDebugEnabled()) { logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]"); } if (logger.isInfoEnabled()) { long elapsedTime = System.currentTimeMillis() - startTime; logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms"); } return this.context; } catch (RuntimeException ex) { logger.error("Context initialization failed", ex); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex); throw ex; } catch (Error err) { logger.error("Context initialization failed", err); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err); throw err; } } /** * 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 * {@link ConfigurableWebApplicationContext} interface. * Can be overridden in subclasses. *

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. * @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 {@link ConfigurableWebApplicationContext} created by this * ContextLoader after config locations have been supplied to the context * but before the context is refreshed. *

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. *

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>> initializerClasses = determineContextInitializerClasses(sc); for (Class> initializerClass : initializerClasses) { Class initializerContextClass = GenericTypeResolver.resolveTypeArgument(initializerClass, ApplicationContextInitializer.class); if (initializerContextClass != null) { Assert.isAssignable(initializerContextClass, wac.getClass(), String.format( "Could not add 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 initializer : this.contextInitializers) { initializer.initialize(wac); } } /** * 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>> determineContextInitializerClasses(ServletContext servletContext) { List>> 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> loadInitializerClass(String className) { try { Class clazz = ClassUtils.forName(className, ClassUtils.getDefaultClassLoader()); Assert.isAssignable(ApplicationContextInitializer.class, clazz); return (Class>) 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 uses * {@link org.springframework.context.access.ContextSingletonBeanFactoryLocator}, * configured via {@link #LOCATOR_FACTORY_SELECTOR_PARAM} and * {@link #LOCATOR_FACTORY_KEY_PARAM}, to load a parent context * which will be shared by all other users of ContextsingletonBeanFactoryLocator * which also use the same configuration parameters. * @param servletContext current servlet context * @return the parent application context, or {@code null} if none * @see org.springframework.context.access.ContextSingletonBeanFactoryLocator */ protected ApplicationContext loadParentContext(ServletContext servletContext) { ApplicationContext parentContext = null; String locatorFactorySelector = servletContext.getInitParameter(LOCATOR_FACTORY_SELECTOR_PARAM); String parentContextKey = servletContext.getInitParameter(LOCATOR_FACTORY_KEY_PARAM); if (parentContextKey != null) { // locatorFactorySelector may be null, indicating the default "classpath*:beanRefContext.xml" BeanFactoryLocator locator = ContextSingletonBeanFactoryLocator.getInstance(locatorFactorySelector); Log logger = LogFactory.getLog(ContextLoader.class); if (logger.isDebugEnabled()) { logger.debug("Getting parent context definition: using parent context key of '" + parentContextKey + "' with BeanFactoryLocator"); } this.parentContextRef = locator.useBeanFactory(parentContextKey); parentContext = (ApplicationContext) this.parentContextRef.getFactory(); } return parentContext; } /** * Close Spring's web application context for the given servlet context. If * the default {@link #loadParentContext(ServletContext)} implementation, * which uses ContextSingletonBeanFactoryLocator, has loaded any shared * parent context, release one reference to that shared parent context. *

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); if (this.parentContextRef != null) { this.parentContextRef.release(); } } } /** * 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 */ public static WebApplicationContext getCurrentWebApplicationContext() { ClassLoader ccl = Thread.currentThread().getContextClassLoader(); if (ccl != null) { WebApplicationContext ccpt = currentContextPerThread.get(ccl); if (ccpt != null) { return ccpt; } } return currentContext; } }

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