1.說明
SpringMVC作為Spring提供的MVC實現，可以實現與Spring的天然無縫聯合，因為具有很廣泛的用途。具體的關於SpringMVC的處理流程邏輯我在這里就不在贅述了。還是來通過源碼來追述下SpringMVC的啟動過程。
2.入口
DispatcherServlet作為SpringMVC的前端控制器，具有很核心的地位。來看下它的繼承結構。
可以看到DispatcherServlet依次繼承了GenericServlet、HttpServlet、HttpServletBean、FrameworkServlet.由於DispatcherServlet是繼承了HttpServlet，所以它的初始化入口應該是HttpServlet的init()方法，Web容器啟動時將調用它的init方法init()方法具體做了什么工作。
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
// Set bean properties from init parameters.
try {
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
throw ex;
}
// Let subclasses do whatever initialization they like.
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}
注意這個方法是final，不能夠被覆蓋，它位於HttpServletBean中。它完成的功能有兩個，第一個將將Servlet初始化參數設置到該Servlet中，第二個調用子類的初始化。
3.HttpServletBean的 initServletBean()
從上面可知，initServletBean方法主要用於子類的處理話過程。看下HttpServletBean的子類FrameworkServlet.看下具體的實現：
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (this.logger.isInfoEnabled()) {
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis();
try {
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
catch (RuntimeException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
if (this.logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
elapsedTime + " ms");
}
}
FrameworkServlet是SpringMVC的一個基礎Servlet，通過它可以完成和Spring的整合。通過initServletBean()的代碼，可知只要操作有兩個initWebApplicationContext();和initFrameworkServlet();第一個完成了Web上下文的初始化工作：ContextLoaderListener 加載了上下文將作為根上下文（DispatcherServlet 的父容器），第二個則提供給子類進行初始化的擴展點：行容器的一些初始化，這個方法由子類實現，來進行擴展。。
我們來看下它是如何完成Web上下文的初始化工作 initWebApplicationContext(); 實現代碼：
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
//在創建的時候注入根上下文
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
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 -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
onRefresh(wac);
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}
return wac;
}
它首先通過Spring提供的工具類 WebApplicationContextUtils 獲取Spring 的根上下文（ContextLoaderListener加載的）。主要操作有1.在創建該Servlet的時候注入根上下文，2.如果上下文為空，那么就查找已經綁定的上下文，如下所示
protected WebApplicationContext findWebApplicationContext() {
String attrName = getContextAttribute();
if (attrName == null) {
return null;
}
WebApplicationContext wac =
WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
if (wac == null) {
throw new IllegalStateException("No WebApplicationContext found: initializer not registered?");
}
return wac;
}
第三個操作，如果沒有找到相應的上下文，並指定父親為ContextLoaderListener，手動創建一個
protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
Class<?> contextClass = getContextClass();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Servlet with name '" + getServletName() +
"' will try to create custom WebApplicationContext context of class '" +
contextClass.getName() + "'" + ", using parent context [" + parent + "]");
}
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException(
"Fatal initialization error in servlet with name '" + getServletName() +
"': custom WebApplicationContext class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
wac.setParent(parent);
wac.setConfigLocation(getContextConfigLocation());
configureAndRefreshWebApplicationContext(wac);
return wac;
}
第四步，不管這個上下文是不是ConfigurableApplicationContext或者在構建的時候刷新過，都需要重新刷新上下文，完成一些初始化的工作。
第四步的實現是放到DispatcherServlet中的onRefresh實現的，具體來看代碼，
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
它主要完成了控制器相關的配置工作，具體工作。。。。好多。。暫緩。
4.總結
SpringMVC初始化啟動過程中做的事情比較簡單，初始化 Spring Web MVC 使用的 Web 上下文並且指定ContextLoaderListener為父容器；還有就是上面代碼所示的那樣初始DispatcherServlet 使用的策略。
未完待續！！！！！！！！