spring学习--ContextLoaderListener工作原理
Posted GLLegolas
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在spring Web中,需要初始化IOC容器,用于存放我们注入的各种对象。当tomcat启动时首先会初始化一个web对应的IOC容器,用于初始化和注入各种我们在web运行过程中需要的对象。当tomcat启动的时候是如何初始化IOC容器的,我们先看一下在web.xml中经常看到的配置:
<context-param> <param-name>contextConfigLocation</param-name> <param-value> classpath:applicationContext.xml </param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>
ContextLoaderListener是一个监听器,其实现了ServletContextListener接口,其用来监听Servlet,当tomcat启动时会初始化一个Servlet容器,这样ContextLoaderListener会监听到Servlet的初始化,这样在Servlet初始化之后我们就可以在ContextLoaderListener中也进行一些初始化操作。看下面的ServletContextListener的源码也是比较简单的,ContextLoaderListener实现了ServletContextListener接口,所以会有两个方法contextInitialized和contextDestroyed。web容器初始化时会调用方法contextInitialized,web容器销毁时会调用方法contextDestroyed。
ContextLoaderListener的方法contextInitialized()的默认实现是在他的父类ContextLoader的initWebApplicationContext方法中实现的,意思就是初始化web应用上下文。他的主要流程就是创建一个IOC容器,并将创建的IOC容器存到servletContext中,ContextLoader的核心实现如下:
initWebApplicationContext函数:
//初始化WebApplicationContext,IOC容器 public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { //判断web容器中是否已经有WebApplicationContext 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. //创建WebApplicationContext if (this.context == null) { //最终得到的是XmlWebApplicationContext this.context = createWebApplicationContext(servletContext); } if (this.context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; //判断应用上下文是否激活 if (!cwac.isActive()) { // The context has not yet been refreshed -> provide services such as // setting the parent context, setting the application context id, etc //判断是否已经有父容器 if (cwac.getParent() == null) { // The context instance was injected without an explicit parent -> // determine parent for root web application context, if any. //获得父容器 ApplicationContext parent = loadParentContext(servletContext); cwac.setParent(parent); } //设置并刷新WebApplicationContext容器 configureAndRefreshWebApplicationContext(cwac, servletContext); } } //将初始化的WebApplicationContext设置到servletContext中 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.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"); } //初始化 WebApplicationContext完成并返回 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; } }
springMVC父容器初始化流程图(盗图)如下:
完整的ContextLoader源码如下:
/** * 用于初始化ApplicationContext * */ public class ContextLoader { //WebApplicationContext id public static final String CONTEXT_ID_PARAM = "contextId"; //配置文件 public static final String CONFIG_LOCATION_PARAM = "contextConfigLocation"; public static final String CONTEXT_CLASS_PARAM = "contextClass"; public static final String CONTEXT_INITIALIZER_CLASSES_PARAM = "contextInitializerClasses"; public static final String GLOBAL_INITIALIZER_CLASSES_PARAM = "globalInitializerClasses"; public static final String LOCATOR_FACTORY_SELECTOR_PARAM = "locatorFactorySelector"; public static final String LOCATOR_FACTORY_KEY_PARAM = "parentContextKey"; private static final String INIT_PARAM_DELIMITERS = ",; "; 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()); } } private static final Map<ClassLoader, WebApplicationContext> currentContextPerThread = new ConcurrentHashMap<ClassLoader, WebApplicationContext>(1); private static volatile WebApplicationContext currentContext; private WebApplicationContext context; private BeanFactoryReference parentContextRef; private final List<ApplicationContextInitializer<ConfigurableApplicationContext>> contextInitializers = new ArrayList<ApplicationContextInitializer<ConfigurableApplicationContext>>(); public ContextLoader() { } public ContextLoader(WebApplicationContext context) { this.context = context; } @SuppressWarnings("unchecked") public void setContextInitializers(ApplicationContextInitializer<?>... initializers) { if (initializers != null) { for (ApplicationContextInitializer<?> initializer : initializers) { this.contextInitializers.add((ApplicationContextInitializer<ConfigurableApplicationContext>) initializer); } } } //初始化WebApplicationContext,IOC容器 public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { //判断web容器中是否已经有WebApplicationContext 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. //创建WebApplicationContext if (this.context == null) { //最终得到的是XmlWebApplicationContext this.context = createWebApplicationContext(servletContext); } if (this.context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; //判断应用上下文是否激活 if (!cwac.isActive()) { // The context has not yet been refreshed -> provide services such as // setting the parent context, setting the application context id, etc //判断是否已经有父容器 if (cwac.getParent() == null) { // The context instance was injected without an explicit parent -> // determine parent for root web application context, if any. //获得父容器 ApplicationContext parent = loadParentContext(servletContext); cwac.setParent(parent); } //设置并刷新WebApplicationContext容器 configureAndRefreshWebApplicationContext(cwac, servletContext); } } //将初始化的WebApplicationContext设置到servletContext中 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.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"); } //初始化 WebApplicationContext完成并返回 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; } } //在web容器加载的时候初始化根WebApplicationContext protected WebApplicationContext createWebApplicationContext(ServletContext sc) { //通过反射获得上下文类 Class<?> contextClass = determineContextClass(sc); if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) { throw new ApplicationContextException("Custom context class [" + contextClass.getName() + "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]"); } //初始化WebApplicationContext,是其实现类XmlWebApplicationContext return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass); } protected Class<?> determineContextClass(ServletContext servletContext) { //查看servlet是否已经存在应用上下文类名 String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM); if (contextClassName != null) { try { //类名不为空则反射获得类 return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader()); } catch (ClassNotFoundException ex) { throw new ApplicationContextException( "Failed to load custom context class [" + contextClassName + "]", ex); } } else { //如果应用上下文类名为空,则获得默认的context上下文名 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); //设置应用上下文id,在web.xml中可以进行配置 if (idParam != null) { wac.setId(idParam); } else { // Generate default id... //如果没有配置则设置默认名称 wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath())); } } //设置ServletContext到容器中 wac.setServletContext(sc); //获得web.xml中配置的contextConfigLocation的值,一般是classpath:applicationContext.xml String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM); if (configLocationParam != null) { //设置加载文件地址 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); //这一步是特别关键的,这样application.xml中的所有配置都会被初始化到XMLWebApplication中 wac.refresh(); } 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) { 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<ConfigurableApplicationContext> initializer : this.contextInitializers) { initializer.initialize(wac); } } protected List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> determineContextInitializerClasses(ServletContext servletContext) { List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> classes = new ArrayList<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>(); 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()); Assert.isAssignable(ApplicationContextInitializer.class, clazz); return (Class<ApplicationContextInitializer<ConfigurableApplicationContext>>) clazz; } catch (ClassNotFoundException ex) { throw new ApplicationContextException("Failed to load context initializer class [" + className + "]", ex); } } //从ServletContext中获取父容器 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; } //通过给定的ServletContext来关闭IOC容器 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(); } } } //在当前线程中获取WebApplicationContext public static WebApplicationContext getCurrentWebApplicationContext() { ClassLoader ccl = Thread.currentThread().getContextClassLoader(); if (ccl != null) { WebApplicationContext ccpt = currentContextPerThread.get(ccl); if (ccpt != null) { return ccpt; } } return currentContext; } }
转自:http://blog.csdn.net/qq924862077/article/details/52769754
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