1.外置tomcat基于SPI的启动流程
tomcat找到我们应用中的默认sping-web包下/META- INF/service/javax.servlet.ServletContainerInitializer
在调用SpringServletContainerInitializer.onStartUp() 之前会找到所有实现了WebApplicationInitializer的类，传入到OnStartup的 webAppInitializerClasses参数中，并传入Servlet上下文对象
org.springframework.web.SpringServletContainerInitializer#onStartup
/**
* Delegate the {@code ServletContext} to any {@link WebApplicationInitializer}
* implementations present on the application classpath.
* <p>Because this class declares @{@code HandlesTypes(WebApplicationInitializer.class)},
* Servlet 3.0+ containers will automatically scan the classpath for implementations
* of Spring's {@code WebApplicationInitializer} interface and provide the set of all
* such types to the {@code webAppInitializerClasses} parameter of this method.
* <p>If no {@code WebApplicationInitializer} implementations are found on the classpath,
* this method is effectively a no-op. An INFO-level log message will be issued notifying
* the user that the {@code ServletContainerInitializer} has indeed been invoked but that
* no {@code WebApplicationInitializer} implementations were found.
* <p>Assuming that one or more {@code WebApplicationInitializer} types are detected,
* they will be instantiated (and <em>sorted</em> if the @{@link
* org.springframework.core.annotation.Order @Order} annotation is present or
* the {@link org.springframework.core.Ordered Ordered} interface has been
* implemented). Then the {@link WebApplicationInitializer#onStartup(ServletContext)}
* method will be invoked on each instance, delegating the {@code ServletContext} such
* that each instance may register and configure servlets such as Spring's
* {@code DispatcherServlet}, listeners such as Spring's {@code ContextLoaderListener},
* or any other Servlet API componentry such as filters.
* @param webAppInitializerClasses all implementations of
* {@link WebApplicationInitializer} found on the application classpath
* @param servletContext the servlet context to be initialized
* @see WebApplicationInitializer#onStartup(ServletContext)
* @see AnnotationAwareOrderComparator
*/
@Override
public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws ServletException {
List<WebApplicationInitializer> initializers = Collections.emptyList();
if (webAppInitializerClasses != null) {
initializers = new ArrayList<>(webAppInitializerClasses.size());
for (Class<?> waiClass : webAppInitializerClasses) {
// 接口和抽象类servlet容器也会给我们，但是我们不要
// 排除接口和容器
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
try {
// 实例化，然后添加到集合中
initializers.add((WebApplicationInitializer)
ReflectionUtils.accessibleConstructor(waiClass).newInstance());
}
catch (Throwable ex) {
throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
}
}
}
}
if (initializers.isEmpty()) {
servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
return;
}
servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
AnnotationAwareOrderComparator.sort(initializers);
// 调用initializer.onStartup 进行扩展
for (WebApplicationInitializer initializer : initializers) {
initializer.onStartup(servletContext);
}
}2. 创建父容器 ContextLoaderListener
org.springframework.web.servlet.support.AbstractDispatcherServletInitializer#onStartup
@Override
public void onStartup(ServletContext servletContext) throws ServletException {
//registerContextLoaderListener ok
super.onStartup(servletContext);
// registerDispatcherServlet
registerDispatcherServlet(servletContext);
}
/**
* Register a {@link ContextLoaderListener} against the given servlet context. The
* {@code ContextLoaderListener} is initialized with the application context returned
* from the {@link #createRootApplicationContext()} template method.
* @param servletContext the servlet context to register the listener against
*/
protected void registerContextLoaderListener(ServletContext servletContext) {
// 创建父容器 ，
WebApplicationContext rootAppContext = createRootApplicationContext();
if (rootAppContext != null) {
ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
// 设置初始化器
listener.setContextInitializers(getRootApplicationContextInitializers());
servletContext.addListener(listener);
}
else {
logger.debug("No ContextLoaderListener registered, as " +
"createRootApplicationContext() did not return an application context");
}
}
3. 创建子容器DispatcherServlet
org.springframework.web.servlet.support.AbstractDispatcherServletInitializer#registerDispatcherServlet
protected void registerDispatcherServlet(ServletContext servletContext) {
String servletName = getServletName();
Assert.hasLength(servletName, "getServletName() must not return null or empty");
// 创建子容器
WebApplicationContext servletAppContext = createServletApplicationContext();
Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null");
// 创建DispatcherServlet
FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
Assert.notNull(dispatcherServlet, "createDispatcherServlet(WebApplicationContext) must not return null");
// 初始化器
dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());
ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
if (registration == null) {
throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " +
"Check if there is another servlet registered under the same name.");
}
// 启动时加载
registration.setLoadOnStartup(1);
// 映射
registration.addMapping(getServletMappings());
// 是否异步支持
registration.setAsyncSupported(isAsyncSupported());
// 设置DispatcherServlet的过滤器
Filter[] filters = getServletFilters();
if (!ObjectUtils.isEmpty(filters)) {
for (Filter filter : filters) {
registerServletFilter(servletContext, filter);
}
}
// 空方法， 可以再对DispatcherServlet进行定制
customizeRegistration(registration);
}
4.初始化ContextLoaderListener
外置tomcat会帮我们调用ContextLoaderListener#contextInitialized 进行初始化；
前面只是创建Spring容器，此处调用configureAndRefreshWebApplicationContext()方法从而调用refresh()方法
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// 设置id
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
// 设置ServletContext到spring上下文
wac.setServletContext(sc);
// 获得servlet容器中的全局参数contextConfigLocation （xml）
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}
// 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
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}
// 在容器加载前 可以通过设置初始化参数contextInitializerClasses、globalInitializerClasses 进行扩展
customizeContext(sc, wac);
// 刷新容器
wac.refresh();
}5. 初始化DispatcherServlet
外置tomcat会帮我们调用DispatcherServlet#init()
最终调用org.springframework.web.servlet.FrameworkServlet#initWebApplicationContext
/**
* Initialize and publish the WebApplicationContext for this servlet.
* <p>Delegates to {@link #createWebApplicationContext} for actual creation
* of the context. Can be overridden in subclasses.
* @return the WebApplicationContext instance
* @see #FrameworkServlet(WebApplicationContext)
* @see #setContextClass
* @see #setContextConfigLocation
*/
protected WebApplicationContext initWebApplicationContext() {
// 获得ContextLoaderListener存的父容器
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// 获得子容器
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// 如果没有设置父容器 spring doGetBean
if (cwac.getParent() == null) {
cwac.setParent(rootContext);
}
// 配置并且加载子容器
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// 从servlet上下文根据<contextAttribute>名字从域里面获取
wac = findWebApplicationContext();
}
if (wac == null) {
// xml会在这里创建
wac = createWebApplicationContext(rootContext);
}
//refreshEventReceived 它会在容器加载完设置为true (通过事件onApplicationEvent)
// springboot在这初始化组件
if (!this.refreshEventReceived) {
synchronized (this.onRefreshMonitor) {
onRefresh(wac);
}
}
if (this.publishContext) {
// 将当前容器放到servlet域中， 可以再创建子容器
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}并且监听子容器的ContextRefreshListener? 去初始化SpringMvc的组件
org.springframework.web.servlet.DispatcherServlet#initStrategies
/**初始化策略,加了s都是多个
* Initialize the strategy objects that this servlet uses.
* <p>May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}tomcat 的流程，后续补充...