- DispatcherServlet UML图
本次分析：HttpServlet->HttpServletBean->FramworkServlet->DispacherServlet
ServletContext是什么？
ServletContext,是一个全局的储存信息的空间，服务器开始，其就存在，服务器关闭，其才释放。request，一个用户可有多个；session，一个用户一个；而servletContext，所有用户共用一个。所以，为了节省空间，提高效率，ServletContext中，要放必须的、重要的、所有用户需要共享的线程又是安全的一些信息。WebApplicationContext是什么？
顾名思义WebApplicationContext是依赖于Web容器的一个Spring的IOC容器。前提条件是web容器启动后这个容器才能启动。那么如何借助web容器来启动Spring web的上下文？HttpServletBean类
public final void init() throws ServletException { if(this.logger.isDebugEnabled()) { this.logger.debug("Initializing servlet ‘" + this.getServletName() + "‘"); } //将Servlet初始化参数设置到该组件上 PropertyValues pvs = new HttpServletBean.ServletConfigPropertyValues(this.getServletConfig(), this.requiredProperties); if(!pvs.isEmpty()) { try { BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this); ResourceLoader resourceLoader = new ServletContextResourceLoader(this.getServletContext()); bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.getEnvironment())); this.initBeanWrapper(bw); bw.setPropertyValues(pvs, true); } catch (BeansException var4) { if(this.logger.isErrorEnabled()) { this.logger.error("Failed to set bean properties on servlet ‘" + this.getServletName() + "‘", var4); } throw var4; } } //交给子类初始化，FrameworkServlet子类的方法覆盖 this.initServletBean(); if(this.logger.isDebugEnabled()) { this.logger.debug("Servlet ‘" + this.getServletName() + "‘ configured successfully"); } }FrameworkServlet类
protected final void initServletBean() throws ServletException {
//省略
//
try {
//初始化web上下文
this.webApplicationContext = this.initWebApplicationContext();
//初始化
this.initFrameworkServlet();
}
//省略
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
//构建并注入一个上下文实例
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) {
//查找已经绑定的上下文
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one 指定为ContextLoaderListener
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;
}从initWebApplicationContext（）方法可以看出，基本上如果ContextLoaderListener加载了上下文将作为根上下文（DispatcherServlet的父容器）。
- DispatcherServlet类
```
**- This implementation calls {@link #initStrategies}.
*/
@Override
//FrameworkServlet中的wac
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
- Initialize the strategy objects that this servlet uses.
May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
//将两种类型的Bean从context里取出来
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
- This implementation calls {@link #initStrategies}.
doDispatchprotected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
//省略...
try {
//省略...
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
//调用所有拦截器的prehandle
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
//调用注册的所有拦截器的posthandle方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
//省略...
//render绘制MV
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
//省略...
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
//省略...
}
}```
1.容器启动时，找到配置文件中的context-param作为键值对放到ServletContext中
2.然后找到listener，容器调用它的contextInitialized(ServletContextEvent event)方法，执行其中的操作
3.spring为我们提供了实现ServletContextListener接口的上下文初始化监听器：ContextLoaderListener
4.spring为我们提供的IOC容器，需要我们指定容器的配置文件，然后由该监听器初始化并创建该容器。要求你指定配置文件的地址及文件名称，一定要使用：contextConfigLocation作为参数名称。
- spring上下文容器配置后，初始化了什么
1、servlet容器启动，为应用创建一个“全局上下文环境”：ServletContext
2、容器调用web.xml中配置的contextLoaderListener，初始化WebApplicationContext上下文环境（即IOC容器），加载context-param指定的配置文件信息到IOC容器中。WebApplicationContext在ServletContext中以键值对的形式保存
3、容器初始化web.xml中配置的servlet，为其初始化自己的上下文信息servletContext，并加载其设置的配置信息到该上下文中。将WebApplicationContext设置为它的父容器。
4、此后的所有servlet的初始化都按照3步中方式创建，初始化自己的上下文环境，将WebApplicationContext设置为自己的父上下文环境。
