在上一节中我们写到DispatcherServlet初始化过程[init()]中的最后一个步骤 initServletBean ，这个步骤比较重要我们重点分析一下。
@Override
protected final void initServletBean() throws ServletException {
// 记录日志 org.apache.catalina.core.ApplicationContext.log Initializing Spring DispatcherServlet 'dispatcherServlet'
getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
// 记录日志
if (logger.isInfoEnabled()) {
// org.springframework.web.servlet.FrameworkServlet.initServletBean Initializing Servlet 'dispatcherServlet'
logger.info("Initializing Servlet '" + getServletName() + "'");
}
// 记录容器启动的开始时间
long startTime = System.currentTimeMillis();
try {
// 因为我们这是一个web应用，所以需要初始化webApplicationContext容器
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException | RuntimeException ex) {
logger.error("Context initialization failed", ex);
throw ex;
}
if (logger.isDebugEnabled()) {
String value = this.enableLoggingRequestDetails ?
"shown which may lead to unsafe logging of potentially sensitive data" :
"masked to prevent unsafe logging of potentially sensitive data";
logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails +
"': request parameters and headers will be " + value);
}
if (logger.isInfoEnabled()) {
logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
}
}
观察上面代码，很容易发现最重要的方法应该为 initWebApplicationContext()
protected WebApplicationContext initWebApplicationContext() {
// 获取webApplicationContext对象，因为第一次由于spring容器还没有初始化，所以现在是获取不到的
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
// 第一次时尚未初始化，所以为null。会走else
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) {
// 换另外一种方式获取webApplicationContext： 根据 contextAttribute 进行获取。第一次同样为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) {
// 创建 webApplicationContext
// 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.
synchronized (this.onRefreshMonitor) {
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
首先SpringMVC会通过两种方式去获取 webApplicationContext对象：（1）通过ServletContext 和 contextAttribute 去获取，首次启动的时候因为没有创建，所以两种方式都不能成功获取，则调用createWebApplicationContext(rootContext)
protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
Class contextClass = getContextClass(); // XmlWebApplicationContext.class;
// 判断XmlWebApplicationContext 是不是ConfigurableWebApplicationContext 的子类
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");
}
// 通过构造器反射创建一个对象
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
// 给XmlWebApplicationContext容器对象设置环境对象
wac.setEnvironment(getEnvironment());
// 设置父容器
wac.setParent(parent);
// 获取config文件地址信息
String configLocation = getContextConfigLocation();
if (configLocation != null) {
// 给XmlWebApplicationContext容器对象设置config文件
wac.setConfigLocation(configLocation);
}
// 配置和刷新XmlWebApplicationContext容器对象
configureAndRefreshWebApplicationContext(wac);
return wac;
}
流程梳理：
第一步： 判断XmlWebApplicationContext（成员变量可能会替换） 是不是ConfigurableWebApplicationContext 的子类，如果不是则抛出异常
第二步：通过构造器反射创建一个XmlWebApplicationContext对象
第三步：给XmlWebApplicationContext容器对象设置环境对象和父容器信息
第四步：把获取到的配置文件位置设置到XmlWebApplicationContext对象的父类AbstractRefreshableConfigApplicationContext的configLocations属性中
第五步：配置和刷新XmlWebApplicationContext容器对象
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
if (this.contextId != null) {
wac.setId(this.contextId);
}
else {
// Generate default id...
// 给xmlWebApplicationContext 设置一个id
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(getServletContext().getContextPath()) + '/' + getServletName());
}
}
// 给xmlWebApplicationContext 设置ServletContext
wac.setServletContext(getServletContext());
// 给xmlWebApplicationContext 设置ServletConfig
wac.setServletConfig(getServletConfig());
// 给xmlWebApplicationContext 设置名命空间 DispatcherServlet-servlet
wac.setNamespace(getNamespace());
// 设置应用监听
wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
// 获取环境变量
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
// 资源的相关的信息做出了一些替换和更新
((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
}
// Spring 未作处理
postProcessWebApplicationContext(wac);
// contextInitializers.size() 为0,未做什么功能
applyInitializers(wac);
// TODO 容器刷新
wac.refresh();
}
以上代码主要是对xmlWebApplicationContext做出一些配置，主要方法应该未refresh()，refresh()为创建容器对象的关键方法，在spring ioc中也调用了该方法，我们以后分析。