javaee標准中，tomcat等web容器啟動時走web.xml 先將各種contex-param 放到servletcontxt中變成parameter，然后開始啟動容器，容器對外提供了listener可在容器onstartup時做一些操作。
log：
二月 25, 2017 2:56:16 下午 org.apache.catalina.core.ApplicationContext log
信息: No Spring WebApplicationInitializer types detected on classpath
解釋：---沒找到自定義的spring WebApplicationInitializer
這句日志來自於： org.springframework.web.SpringServletContainerInitializer 在spring-web-x.x.x.Release.jar 包中。
該類實現了servletContainerInitializer 接口的onStartup方法。此接口只有一個方法。這是spring3.1之后的新特性，無web.xml 而是基於代碼注解的配置啟動servlet。引入了servlet3.0.
* @param c the Set of application classes that extend, implement, or
* have been annotated with the class types specified by the
* {@link javax.servlet.annotation.HandlesTypes HandlesTypes} annotation,
* or <tt>null</tt> if there are no matches, or this
* <tt>ServletContainerInitializer</tt> has not been annotated with
* <tt>HandlesTypes</tt>
c這個param比較有意思，需要實現類增加@HandlesTypes(xx.class)注解。如spring的實現類聲明了注解
@HandlesTypes(WebApplicationInitializer.class) 所以spring基於java代碼的配置是需要實現WebApplicationInitializer接口的。
@since Servlet 3.0
public interface ServletContainerInitializer {
public void onStartup(Set<Class<?>> c, ServletContext ctx)
throws ServletException;
}
查看此接口的注釋
<p>Implementations of this interface must be declared by a JAR file * resource located inside the <tt>META-INF/services</tt> directory and * named for the fully qualified class name of this interface, and will be * discovered using the runtime's service provider lookup mechanism
* or a container specific mechanism that is semantically equivalent to * it.
大概意思是講 必須在該接口所在項目的META-INF/services/文件夾下 生成一個文件名字為javax.serlvet.ServletContainerInitializer的文件，內容要與ServletContainerInitializer接口的實現類的全路徑一樣才能被發現。
仔細看spring-web包下 有類似的結構。聲明為了javax.servlet.ServletContainerInitializer的文件，內容為 org.springframework.web.SpringServletContainerInitializer
日志來自於實現類：SpringServletContainerInitializer上一段源碼：
@Override
public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws ServletException {
List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>();
if (webAppInitializerClasses != null) {
for (Class<?> waiClass : webAppInitializerClasses) {
// Be defensive: Some servlet containers provide us with invalid classes,
// no matter what @HandlesTypes says...
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
try {
initializers.add((WebApplicationInitializer) 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;
}
AnnotationAwareOrderComparator.sort(initializers);
servletContext.log("Spring WebApplicationInitializers detected on classpath: " + initializers);
for (WebApplicationInitializer initializer : initializers) {
initializer.onStartup(servletContext);
}
}
因為沒有使用基於servlet3.0規范的類，所以有這一條日志。
log：
Initializing Spring root WebApplicationContext
解釋：日志是由類
WebApplicationContextorg.springframework.web.context.ContextLoader.initWebApplicationContext(ServletContext servletContext)打印的，contextLoader作為ContextLoaderListener的private 變量。標識着啟動wac。核心代碼在wac.refresh()中。
值得注意的是注冊核心類之前，會先處理beanFactory的PostProcesors類。
這些類一般都實現了
BeanFactoryPostProcessor 這個接口。通常講抽象類PropertyResourceConfigurer比較重要。
org.springframework.beans.factory.config.PropertyResourceConfigurer
源碼注釋：
/* Allows for custom modification of an application context's bean definitions, * adapting the bean property values of the context's underlying bean factory. * * <p>Application contexts can auto-detect BeanFactoryPostProcessor beans in * their bean definitions and apply them before any other beans get created. * * <p>Useful for custom config files targeted at system administrators that * override bean properties configured in the application context.
*/
LOG:
2017-02-25 19:29:08:719 INFO [mvc.annotation.DefaultAnnotationHandlerMapping] Mapped URL path
解釋：
啟動wac時，會由讀取@RequestMapping 注解拼接url ，並緩存 {url,method}的映射關系。
LOG:
二月 25, 2017 7:40:29 下午 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring FrameworkServlet 'led'
2017-02-25 19:40:29:584 INFO [web.servlet.DispatcherServlet] FrameworkServlet 'led': initialization started
2017-02-25 19:40:29:603 INFO [context.support.XmlWebApplicationContext] Refreshing WebApplicationContext for namespace 'led-servlet': startup date [Sat Feb 25 19:40:29 CST 2017]; parent: Root WebApplicationContext
2017-02-25 19:40:29:605 INFO [factory.xml.XmlBeanDefinitionReader] Loading XML bean definitions from ServletContext resource [/WEB-INF/led-servlet.xml]
解釋：開始啟動servlet，配置為DispatcherServlet 並執行父類 FrameworkServlet 的父類 HttpServletBean的init方法，並鈎子調用FrameworkServlet的initServletBean()創建servlet容器 放到servletContext
setAttribute(Framework.class.getName()+".CONTEXT"+ServletName,WAC);並且將WAC的parent設置為ContextLoaderListener創建的WAC。
至此SpringMVC啟動完畢。
更加詳細的內容下一篇隨筆。