深入分析Spring 与 Spring MVC容器

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {

//PS : ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE=WebApplicationContext.class.getName() + ".ROOT" 根上下文的名称

//PS : 默认情况下，配置文件的位置和名称是： DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml"

//在整个web应用中，只能有一个根上下文

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.

if (this.context == null) {

// 在这里执行了创建WebApplicationContext的操作

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) {

// 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);

}

configureAndRefreshWebApplicationContext(cwac, servletContext);

}

}

// PS: 将根上下文放置在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");

}

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;

}

}

protected WebApplicationContext createWebApplicationContext(ServletContext sc, ApplicationContext parent) {

//根据web.xml中的配置决定使用何种WebApplicationContext。默认情况下使用XmlWebApplicationContext

//web.xml中相关的配置context-param的名称“contextClass”

Class<?> contextClass = determineContextClass(sc);

if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {

throw new ApplicationContextException("Custom context class [" + contextClass.getName() + "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");

}

//实例化WebApplicationContext的实现类

ConfigurableWebApplicationContext wac = (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

// Assign the best possible id value.

if (sc.getMajorVersion() == 2 && sc.getMinorVersion() < 5) {

// Servlet <= 2.4: resort to name specified in web.xml, if any.

String servletContextName = sc.getServletContextName();

if (servletContextName != null) {

wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + servletContextName);

} else {

wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX);

}

} else {

// Servlet 2.5's getContextPath available!

wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + sc.getContextPath());

}

wac.setParent(parent);

wac.setServletContext(sc);

//设置spring的配置文件

wac.setConfigLocation(sc.getInitParameter(CONFIG_LOCATION_PARAM));

customizeContext(sc, wac);

//spring容器初始化

wac.refresh();

return wac;

}

1. ContextLoaderListener构建Root Context时序图：

protected WebApplicationContext initWebApplicationContext() {

//先从web容器的ServletContext中查找WebApplicationContext

WebApplicationContext wac = findWebApplicationContext();

if (wac == null) {

// No fixed context defined for this servlet - create a local one.

//从ServletContext中取得根上下文

WebApplicationContext parent = WebApplicationContextUtils.getWebApplicationContext(getServletContext());

//创建Spring MVC的上下文，并将根上下文作为起双亲上下文

wac = createWebApplicationContext(parent);

}

if (!this.refreshEventReceived) {

// Apparently not a ConfigurableApplicationContext with refresh support:

// triggering initial onRefresh manually here.

onRefresh(wac);

}

if (this.publishContext) {

// Publish the context as a servlet context attribute.

// 取得context在ServletContext中的名称

String attrName = getServletContextAttributeName();

//将Spring MVC的Context放置到ServletContext中

getServletContext().setAttribute(attrName, wac);

if (this.logger.isDebugEnabled()) {

this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() + "' as ServletContext attribute with name [" + attrName + "]");

}

}

return wac;

}

1. DispatcherServlet初始化的大体流程：

1. 控制器DispatcherServlet的类图及继承关系：

servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);