SpringMVC源码阅读-Root WebApplicationContext初始化(一)
说明
Root WebApplicationContext 因为容器有父子关系 只是表示是最父级WebApplicationContext WebApplicationContext是一个接口 默认使用的是XmlWebApplicationContext
1.传统spring mvc配置
<!-- 省略非关键的配置 --> <!-- [1] Spring配置 --> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> <!-- 指定Spring Bean的配置文件所在目录。默认配置在WEB-INF目录下 --> <context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:config/applicationContext.xml</param-value> </context-param> <!-- ====================================== --> <!-- [2] Spring MVC配置 --> <servlet> <servlet-name>spring</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <!-- 可以自定义servlet.xml配置文件的位置和名称，默认为WEB-INF目录下，名称为[<servlet-name>]-servlet.xml，如spring-servlet.xml <init-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/spring-servlet.xml</param-value> // 默认 </init-param> --> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>spring</servlet-name> <url-pattern>*.do</url-pattern> </servlet-mapping>
现在spring boot已经不需要配置了。通过自动配置代替了手动配置。但是这些配置还是存在
ContextLoaderListener
作用是在启动tomcat 或者jetty服务器的时候初始化一个Root Spring WebApplicationContext
public class ContextLoaderListener extends ContextLoader implements ServletContextListener { public ContextLoaderListener() { } public ContextLoaderListener(WebApplicationContext context) { super(context); } //负责初始化容器 public void contextInitialized(ServletContextEvent event) {
//<1> this.initWebApplicationContext(event.getServletContext()); } //负责销毁容器 public void contextDestroyed(ServletContextEvent event) { this.closeWebApplicationContext(event.getServletContext()); ContextCleanupListener.cleanupAttributes(event.getServletContext()); } }
<1>initWebApplicationContext
org.springframework.web.context.ContextLoader#initWebApplicationContext
/** * WebApplicationContext.class.getName() + ".ROOT" * @param servletContext * @return */ public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { /** * * 因为初始化后会set到setvletConontext * WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE=WebApplicationContext.class.getName() + ".ROOT" * 防止重复初始化root 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!"); } else { 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 { if (this.context == null) { /** * <2> *获得对应的context * 1.servletContext.getInitParameter("contextClass")是否有配置自定义容器 * 2.默认是没有配置 所以获得的是org.springframework.web.context.support.XmlWebApplicationContext 解析xml */ this.context = this.createWebApplicationContext(servletContext); } /** * 判断是否实现了ConfigurableWebApplicationContext */ if (this.context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)this.context; //判断是否激活 if (!cwac.isActive()) { //如果没有父节点 则获取sevletContext的rootjie if (cwac.getParent() == null) { /** * <4> * 这里会获取context-param key为locatorFactorySelector 配置的xml * 同时获取析context-param key 为parentContextKey的bean 这个bean必须实现BeanFactory 和ApplicationContext 主要是我们自定义容器 * 并以这个容器作为root容器 */ ApplicationContext parent = this.loadParentContext(servletContext); cwac.setParent(parent); } /** * <3> * 获取servetContext的initParameter key为:contextId值作为初始化容器的id * 如果没有默认是使用org.springframework.web.context.WebApplicationContext:+servletContext.getContextPath() * 解析xml执行初始化 */ this.configureAndRefreshWebApplicationContext(cwac, servletContext); } } /** * 将容器设置到servletContext后续我们可以通过servleteContext获取到 */ 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"); } return this.context; } catch (RuntimeException var8) { logger.error("Context initialization failed", var8); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var8); throw var8; } catch (Error var9) { logger.error("Context initialization failed", var9); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var9); throw var9; } } }
<2>createWebApplicationContext
快速返回:<1>
org.springframework.web.context.ContextLoader#initWebApplicationContext
->
org.springframework.web.context.ContextLoader#createWebApplicationContext
protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
//根据配置获取容器的类型 Class<?> contextClass = this.determineContextClass(sc); /** * 判断contextClass 是否是ConfigurableWebApplicationContext类型或者子类型 * 就是是否能强转 */ if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) { throw new ApplicationContextException("Custom context class [" + contextClass.getName() + "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]"); } else { //创建对象 并强转为ConfigurableWebApplicationContext return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass); } } protected Class<?> determineContextClass(ServletContext servletContext) { /** * 是否有配置自定义的context容器 * 在servletContext获取 key:contextClass */ String contextClassName = servletContext.getInitParameter("contextClass"); if (contextClassName != null) { try { //反射创建自定义配置 return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader()); } catch (ClassNotFoundException var4) { throw new ApplicationContextException("Failed to load custom context class [" + contextClassName + "]", var4); } } else { /** * 获取默认配置 这里是XMLWebApplicationContext 从ContextLoader.properties 根据class名字获取配置 */ contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName()); try { //反射创建 return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader()); } catch (ClassNotFoundException var5) { throw new ApplicationContextException("Failed to load default context class [" + contextClassName + "]", var5); } } }
<3>configureAndRefreshWeb...
org.springframework.web.context.ContextLoader#initWebApplicationContext
->
org.springframework.web.context.ContextLoader#configureAndRefreshWebApplicationContext
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) { String configLocationParam; if (ObjectUtils.identityToString(wac).equals(wac.getId())) { configLocationParam = sc.getInitParameter("contextId"); if (configLocationParam != null) { wac.setId(configLocationParam); } else { wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath())); } } wac.setServletContext(sc); /** * 这里会获取到我们配置的spring xml地址 * <context-param> * <param-name>contextConfigLocation</param-name> * <param-value> * classpath:application-wemall.xml * </param-value> * </context-param> */ configLocationParam = sc.getInitParameter("contextConfigLocation"); if (configLocationParam != null) { //放到容器 wac.setConfigLocation(configLocationParam); } ConfigurableEnvironment env = wac.getEnvironment(); if (env instanceof ConfigurableWebEnvironment) { ((ConfigurableWebEnvironment)env).initPropertySources(sc, (ServletConfig)null); } this.customizeContext(sc, wac); /** *执行容器初始化 */ wac.refresh(); }
<4>loadParentContext
快速返回:<1>
org.springframework.web.context.ContextLoader#initWebApplicationContext
->
org.springframework.web.context.ContextLoader#loadParentContext
protected ApplicationContext loadParentContext(ServletContext servletContext) { ApplicationContext parentContext = null; /** * 获取key为locatorFactorySelector 存储了spring xml地址 如:springContext.xml */ String locatorFactorySelector = servletContext.getInitParameter("locatorFactorySelector"); /** * 配置里面容器的bean id */ String parentContextKey = servletContext.getInitParameter("parentContextKey"); /** * 下面会解析配置的xml 并获取容器 */ if (parentContextKey != null) { 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; }
text.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="remoteOssClient" class="com.bozhi.wemall.SimepleBeanFactory"> </bean> </beans>
web.xml
<context-param> <param-name>locatorFactorySelector</param-name> <param-value>classpath:test.xml</param-value> </context-param> <context-param> <param-name>parentContextKey</param-name> <param-value>remoteOssClient</param-value> </context-param>
总结
1.root WebApplictonContext由servlet Listener ContextLoaderListener 进行初始化
2.默认是通过XmlWebApplicationContext作为容器 我们可以通过再ServletContext设置key为contextClass的Attribute指定容器class全名称 必须实现ConfigurableWebApplicationContext
2.初始化完成后会放置到servlteContext Attribute 后续我们可以获取
3.我们可以通过配置context param locatorFactorySelector parentContextKey 自定义root容器
4.后续Servlet的初始化的容器的parent 则指向root
