Spring源码分析(一)
以下源码基于Spring 5.2.5版本
使用XML方式配置Spring应用时,web.xml中会配置一个Listener,如下:
<display-name>Web Application</display-name> <context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:config/spring-all.xml</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>
其中classpath:config/spring-all.xml指明了spring配置文件的位置,而ContextLoaderListener是一个监听器,当Web容器启动的时候回去实例化这个监听器
public class ContextLoaderListener extends ContextLoader implements ServletContextListener
1、首先会实例化ContextLoaderListener的父类,执行ContextLoader的静态代码块
static { 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()); } }
这段代码读取了ContextLoader.properties中的内容,如下:
org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext
2、执行ContextLoaderListener的
public void contextInitialized(ServletContextEvent event) { initWebApplicationContext(event.getServletContext()); }
initWebApplicationContext代码如下:
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 { // 重点: //实例化XmlWebApplicationContext //这个上下文的类型是由刚刚从ContextLoader.properties中读取到的内容决定的 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) { ApplicationContext parent = loadParentContext(servletContext); cwac.setParent(parent); } //进行Bean的解析,加载和初始化 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; } }
configureAndRefreshWebApplicationContext(cwac, servletContext)进行Bean的解析,加载和初始化,源码如下:
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) { if (ObjectUtils.identityToString(wac).equals(wac.getId())) { String idParam = sc.getInitParameter(CONTEXT_ID_PARAM); if (idParam != null) { wac.setId(idParam); } else { wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath())); } } wac.setServletContext(sc); //读取web.xml中配置的Spring配置文件的位置 String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM); if (configLocationParam != null) { wac.setConfigLocation(configLocationParam); } ConfigurableEnvironment env = wac.getEnvironment(); if (env instanceof ConfigurableWebEnvironment) { ((ConfigurableWebEnvironment) env).initPropertySources(sc, null); } customizeContext(sc, wac); //用于扩展操作; wac.refresh(); }
wac.refresh()用于进行Spring中Bean的加载;refresh()方法在AbstractApplicationContext中实现
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset ‘active‘ flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring‘s core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }
具体实现细节下面再分别进行介绍