初探spring applicationContext在web容器中加载过程

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<context-param> <param-name>webAppRootKey</param-name> <param-value>task.root</param-value> </context-param> <!-- 定义SPRING配置文件 --> <context-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/taskContext*.xml</param-value> </context-param> <context-param> <param-name>log4jConfigLocation</param-name> <param-value>/WEB-INF/log4j.properties</param-value> </context-param> <!-- 定义LOG4J监听器 --> <listener> <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class> </listener>   <!-- 定义SPRING监听器 --> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>

进入contextLoaderListener看看到底加载时做了甚么 ==>org.springframework.web.context.ContextLoaderListener

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public class ContextLoaderListener implements ServletContextListener {   private ContextLoader contextLoader;   /** * Initialize the root web application context. */ //当WEB上下文初始化时,系统会调用此方法 public void contextInitialized(ServletContextEvent event) { this.contextLoader = createContextLoader();   //监听到WEB上下文初始化的时候执行SPRING上下文contextLoader的初始化工作 this.contextLoader.initWebApplicationContext(event.getServletContext()); }   /** * Create the ContextLoader to use. Can be overridden in subclasses. * @return the new ContextLoader */ protected ContextLoader createContextLoader() { return new ContextLoader(); }   /** * Return the ContextLoader used by this listener. */ public ContextLoader getContextLoader() { return contextLoader; }   /** * Close the root web application context. */ public void contextDestroyed(ServletContextEvent event) { if (this.contextLoader != null ) { this.contextLoader.closeWebApplicationContext(event.getServletContext()); } }   }

看一下是怎么来初始化webapplicationContext的 ==>contextLoader.initWebApplicationContext

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public WebApplicationContext initWebApplicationContext(ServletContext servletContext) throws IllegalStateException, BeansException {   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!" ); }   long startTime = System.currentTimeMillis(); if (logger.isInfoEnabled()) { logger.info("Root WebApplicationContext: initialization started" ); } servletContext.log("Loading Spring root WebApplicationContext" );   try { // Determine parent for root web application context, if any. ApplicationContext parent = loadParentContext(servletContext);   // Store context in local instance variable, to guarantee that // it is available on ServletContext shutdown.   //创建web上下文 this.context = createWebApplicationContext(servletContext, parent); servletContext.setAttribute( WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);   if (logger.isInfoEnabled()) { logger.info("Using context class [" + this.context.getClass().getName() + "] for root WebApplicationContext" ); } if (logger.isDebugEnabled()) { logger.debug("Published root WebApplicationContext [" + this.context + "] 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; } }

==>contextLoader.createWebApplicationContext(servletContext, parent);

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protected WebApplicationContext createWebApplicationContext( ServletContext servletContext, ApplicationContext parent) throws BeansException { //根据servletContext来决定要实例化的WebApplicationContext Class contextClass = determineContextClass(servletContext); if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) { throw new ApplicationContextException("Custom context class [" + contextClass.getName() + "] is not of type ConfigurableWebApplicationContext" ); } ConfigurableWebApplicationContext wac = (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass); wac.setParent(parent); wac.setServletContext(servletContext);   //得到WEB.XML中设置的SPRING配置文件位置 String configLocation = servletContext.getInitParameter(CONFIG_LOCATION_PARAM); if (configLocation != null ) { //把配置文件分段后设置到WebApplicationContext的ConfigLocations中 wac.setConfigLocations(StringUtils.tokenizeToStringArray(configLocation, ConfigurableWebApplicationContext.CONFIG_LOCATION_DELIMITERS)); } //刷新WebApplicationContext wac.refresh(); return wac; }

==>contextLoader.determineContextClass(servletContext);

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protected Class determineContextClass(ServletContext servletContext) throws ApplicationContextException { //获得需要实例化的CONTEXT类名,在web.xml中有设置,如果没有设置,那么为空 String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM); if (contextClassName != null ) { try { return ClassUtils.forName(contextClassName); } catch (ClassNotFoundException ex) { throw new ApplicationContextException( "Failed to load custom context class [" + contextClassName + "]" , ex); } } //如果在spring web.xml中没有设置context类位置,那么取得默认context else { //取得defaultStrategies配置文件中的WebApplicationContext属性 contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName()); try { return ClassUtils.forName(contextClassName); } catch (ClassNotFoundException ex) { throw new ApplicationContextException( "Failed to load default context class [" + contextClassName + "]" , ex); } } }

SPRING上下文默认的策略是甚么呢? ==>contextLoader.defaultStrategies

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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 { //设置classpath为contextLoader同级目录 ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class); //加载该目录下的所有properties文件 defaultStrategies = PropertiesLoaderUtils.loadProperties(resource); } catch (IOException ex) { throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage()); } }

找到同级目录下的配置文件 ==>ContextLoader.properties

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# Default WebApplicationContext implementation class for ContextLoader. # Used as fallback when no explicit context implementation has been specified as context-param. # Not meant to be customized by application developers.   #默认的WebApplicationContext为org.springframework.web.context.support.XmlWebApplicationContext org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

==>org.springframework.web.context.support.XmlWebApplicationContext

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public class XmlWebApplicationContext extends AbstractRefreshableWebApplicationContext {   /** Default config location for the root context */   //配置了默认的spring配置文件 public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml" ;   //配置文件默认BUILD路径 public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/" ;   //配置文件默认后缀名 public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml" ;   /** * Loads the bean definitions via an XmlBeanDefinitionReader. * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader * @see #initBeanDefinitionReader * @see #loadBeanDefinitions */ //获得bean配置 protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws IOException { //从BEAN工厂获得一个XmlBeanDefinitionReader 来读取SPRING配置文件 XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);   //设置beanDefinitionReader服务于当前CONTEXT // resource loading environment. beanDefinitionReader.setResourceLoader(this ); beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this ));   // Allow a subclass to provide custom initialization of the reader, // then proceed with actually loading the bean definitions. initBeanDefinitionReader(beanDefinitionReader); //读取配置文件 loadBeanDefinitions(beanDefinitionReader); }   /** * Initialize the bean definition reader used for loading the bean * definitions of this context. Default implementation is empty. * <p>Can be overridden in subclasses, e.g. for turning off XML validation * or using a different XmlBeanDefinitionParser implementation. * @param beanDefinitionReader the bean definition reader used by this context * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setValidationMode * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setDocumentReaderClass */ protected void initBeanDefinitionReader(XmlBeanDefinitionReader beanDefinitionReader) { }   /** * Load the bean definitions with the given XmlBeanDefinitionReader. * <p>The lifecycle of the bean factory is handled by the refreshBeanFactory method; * therefore this method is just supposed to load and/or register bean definitions. * <p>Delegates to a ResourcePatternResolver for resolving location patterns * into Resource instances. * @throws org.springframework.beans.BeansException in case of bean registration errors * @throws java.io.IOException if the required XML document isn't found * @see #refreshBeanFactory * @see #getConfigLocations * @see #getResources * @see #getResourcePatternResolver */ //读取配置文件 protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException { String[] configLocations = getConfigLocations(); if (configLocations != null ) { for (int i = 0; i < configLocations.length; i++) { reader.loadBeanDefinitions(configLocations[i]); } } }   /** * The default location for the root context is "/WEB-INF/applicationContext.xml", * and "/WEB-INF/test-servlet.xml" for a context with the namespace "test-servlet" * (like for a DispatcherServlet instance with the servlet-name "test"). */ //获得默认的ConfigLocations protected String[] getDefaultConfigLocations() { if (getNamespace() != null ) { return new String[] { DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() +   DEFAULT_CONFIG_LOCATION_SUFFIX} ; } else { return new String[] { DEFAULT_CONFIG_LOCATION} ; } }