1. Web应用上下文环境创建简析
通过上一节的分析,找到了SpringMVC源码分析的入口,接下来看Web应用上下文环境创建过程。打开ContextLoader类的initWebApplicationContext方法:
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 { // 将上下文存储在本地实例变量中,以确保它在ServletContext关闭时可用。 // Store context in local instance variable, to guarantee that it is available on ServletContext shutdown. if (this.context == null) { // 1.创建web应用上线文环境 this.context = createWebApplicationContext(servletContext); } if (this.context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; // 如果当前上下文环境未激活,那么其只能提供例如设置父上下文、设置上下文id等功能 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); } // 2.配置并刷新当前上下文环境 configureAndRefreshWebApplicationContext(cwac, servletContext); } } // 将当前上下文环境存储到ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE变量中 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.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; } }
该方法一共涉及两个比较重要的点:
- 创建web应用上线文环境
- 配置并刷新当前上下文环境
2. 创建web应用上线文环境
/** * 为当前类加载器实例化根WebApplicationContext,可以是默认上线文加载类或者自定义上线文加载类 */ protected WebApplicationContext createWebApplicationContext(ServletContext sc) { // 1.确定实例化WebApplicationContext所需的类 Class<?> contextClass = determineContextClass(sc); if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) { throw new ApplicationContextException("Custom context class [" + contextClass.getName() + "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]"); } // 2.实例化得到的WebApplicationContext类 return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass); }
逻辑很简单,得到一个类,将其实例化。我们经常说的web应用上下文环境,是不是比我们想象的还要简单。。。
那么要得到或者明确哪个类呢? 继续看代码:
/** * 返回WebApplicationContext(web应用上线文环境)实现类 * 如果没有自定义默认返回XmlWebApplicationContext类 * * 两种方式: * 1。非自定义:通过ContextLoader类的静态代码块加载ContextLoader.properties配置文件并解析,该配置文件中的默认类即XmlWebApplicationContext * 2。自定义: 通过在web.xml文件中,配置context-param节点,并配置param-name为contextClass的自己点,如 * <context-param> * <param-name>contextClass</param-name> * <param-value>org.springframework.web.context.support.MyWebApplicationContext</param-value> * </context-param> * * 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); // 1.自定义 if (contextClassName != null) { try { return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader()); } catch (ClassNotFoundException ex) { throw new ApplicationContextException("Failed to load custom context class [" + contextClassName + "]", ex); } } // 2.默认 else { // 根据静态代码块的加载这里 contextClassName = XmlWebApplicationContext 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); } } }
自定义方式注释里已经写的很清晰了,我们来看默认方式,这里涉及到了一个静态变量defaultStrategies,并在下面的静态代码块中对其进行了初始化操作:
private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties"; private static final Properties defaultStrategies; /** * 静态代码加载默认策略,即默认的web应用上下文 * DEFAULT_STRATEGIES_PATH --> ContextLoader.properties * * org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext */ 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()); } }
这段代码对ContextLoader.properties进行了解析,那么ContextLoader.properties中存储的内容是什么呢?
# 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. org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext
很简单,通过上面的操作,我们就可以确定contextClassName是XmlWebApplicationContext,跟我们之前分析的ApplicationContext差不多,只是在其基础上又提供了对web的支持。接下来通过BeanUtils.instantiateClass(contextClass)将其实例化即可。
3.配置并刷新当前上下文环境
/** * 配置并刷新当前web应用上下文 */ protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) { /** * 1.配置应用程序上下文id * 如果当前应用程序上下文id仍然设置为其原始默认值,则尝试为其设置自定义上下文id,如果有的话。 * 在web.xml中配置 * <context-param> * <param-name>contextId</param-name> * <param-value>jack-2019-01-02</param-value> * </context-param> */ if (ObjectUtils.identityToString(wac).equals(wac.getId())) { String idParam = sc.getInitParameter(CONTEXT_ID_PARAM); if (idParam != null) { wac.setId(idParam); } // 无自定义id则为其生成默认id else { wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath())); } } wac.setServletContext(sc); /** * 2.设置配置文件路径,如 * <context-param> * <param-name>contextConfigLocation</param-name> * <param-value>classpath:spring-context.xml</param-value> * </context-param> */ 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 // 3.创建ConfigurableEnvironment并配置初始化参数 ConfigurableEnvironment env = wac.getEnvironment(); if (env instanceof ConfigurableWebEnvironment) { ((ConfigurableWebEnvironment) env).initPropertySources(sc, null); } // 4.自定义配置上下文环境 customizeContext(sc, wac); // 5.刷新上下文环境 wac.refresh(); }
前三个步骤比较简单,在前面的博客中多少有些介绍,我们来看自定义配置上下文环境和刷新上下文环境
3.1 自定义配置上下文环境
protected void customizeContext(ServletContext sc, ConfigurableWebApplicationContext wac) { /** * 加载并实例化web.xml配置文件中的 globalInitializerClasses 和 contextInitializerClasses 配置 * * globalInitializerClasses 代表所有的web application都会应用 * contextInitializerClasses 代表只有当前的web application会使用 * 例如,在web.xml配置文件中: * <context-param> * <param-name>contextInitializerClasses</param-name> * <param-value>com.lyc.cn.init.MyContextInitializerClasses</param-value> * </context-param> * * 容器将会调用自定义的initialize方法,其实就在这段代码的下方。。。 */ 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); } }
该实现很简单,我们只要在web.xml中自定义contextInitializerClasses和globalInitializerClasses并提供实现类即可:
如:
<context-param> <param-name>contextInitializerClasses</param-name> <param-value>com.lyc.cn.init.MyContextInitializerClasses</param-value> </context-param>
public class MyContextInitializerClasses implements ApplicationContextInitializer<XmlWebApplicationContext> { /** * Initialize the given application context. * @param applicationContext the application to configure */ @Override public void initialize(XmlWebApplicationContext applicationContext) { System.out.println("MyContextInitializerClasses initialize ..."); System.out.println("MyContextInitializerClasses " + applicationContext.toString()); } }
3.2 刷新上下文环境
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // 1、准备刷新上下文环境 prepareRefresh(); // 2、读取xml并初始化BeanFactory ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // 3、填充BeanFactory功能 prepareBeanFactory(beanFactory); try { // 4、子类覆盖方法额外处理(空方法) postProcessBeanFactory(beanFactory); // 5、调用BeanFactoryPostProcessor invokeBeanFactoryPostProcessors(beanFactory); // 6、注册BeanPostProcessors registerBeanPostProcessors(beanFactory); // 7、初始化Message资源 initMessageSource(); // 8、初始事件广播器 initApplicationEventMulticaster(); // 9、留给子类初始化其他Bean(空的模板方法) onRefresh(); // 10、注册事件监听器 registerListeners(); // 11、初始化其他的单例Bean(非延迟加载的) finishBeanFactoryInitialization(beanFactory); // 12、完成刷新过程,通知生命周期处理器lifecycleProcessor刷新过程,同时发出ContextRefreshEvent通知 finishRefresh(); } catch (BeansException ex) { // 13、销毁已经创建的Bean destroyBeans(); // 14、重置容器激活标签 cancelRefresh(ex); throw ex; } finally { resetCommonCaches(); } } }
这段代码在前面的博客中已经详细的分析过了,感兴趣的同学查看前面的博客吧! 到这里Web应用上下文环境创建过程就结束了。