SpringMVC執行過程詳細講解

2022-08-30 18:04:07

SpringMVC常用元件

DispatcherServlet：前端控制器，不需要工程師開發，由框架提供

作用：統一處理請求和響應，整個流程控制的中心，由它呼叫其它元件處理使用者的請求

HandlerMapping：處理器對映器，不需要工程師開發，由框架提供

作用：根據請求的url、method等資訊查詢Handler，即控制器方法

Handler：處理器，需要工程師開發

作用：在DispatcherServlet的控制下Handler對具體的使用者請求進行處理

HandlerAdapter：處理器介面卡，不需要工程師開發，由框架提供

作用：通過HandlerAdapter對處理器（控制器方法）進行執行

ViewResolver：檢視解析器，不需要工程師開發，由框架提供

作用：進行檢視解析，得到相應的檢視，例如：ThymeleafView、InternalResourceView、

RedirectView

View：檢視

作用：將模型資料通過頁面展示給使用者

DispatcherServlet初始化過程

DispatcherServlet 本質上是一個 Servlet，所以天然的遵循 Servlet 的生命週期。所以宏觀上是 Servlet生命週期來進行排程。

初始化WebApplicationContext

所在類：org.springframework.web.servlet.FrameworkServle

protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
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
// 建立WebApplicationContext
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.
synchronized (this.onRefreshMonitor) {
// 重新整理WebApplicationContext
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
// 將IOC容器在應用域共用
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}

②建立WebApplicationContext

所在類：org.springframework.web.servlet.FrameworkServlet

protected WebApplicationContext createWebApplicationContext(@Nullable
ApplicationContext parent) {
Class<?> contextClass = getContextClass();
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");
}
// 通過反射建立 IOC 容器物件
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext)
BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
// 設定父容器
wac.setParent(parent);
String configLocation = getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
configureAndRefreshWebApplicationContext(wac);
return wac;
}

③DispatcherServlet初始化策略

FrameworkServlet建立WebApplicationContext後，重新整理容器，呼叫onRefresh(wac)，此方法在DispatcherServlet中進行了重寫，呼叫了initStrategies(context)方法，初始化策略，即初始化

DispatcherServlet的各個元件

所在類：org.springframework.web.servlet.DispatcherServlet

protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}