从springmvc启动日志学习

javaee标准中，tomcat等web容器启动时走web.xml 先将各种contex-param 放到servletcontxt中变成parameter，然后开始启动容器，容器对外提供了listener可在容器onstartup时做一些操作。

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

解释：---没找到自定义的spring WebApplicationInitializer

这句日志来自于： org.springframework.web.SpringServletContainerInitializer 在spring-web-x.x.x.Release.jar 包中。

该类实现了servletContainerInitializer 接口的onStartup方法。此接口只有一个方法。这是spring3.1之后的新特性，无web.xml 而是基于代码注解的配置启动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这个param比较有意思，需要实现类增加@HandlesTypes(xx.class)注解。如spring的实现类声明了注解

@HandlesTypes(WebApplicationInitializer.class) 所以spring基于java代码的配置是需要实现WebApplicationInitializer接口的。

@since Servlet 3.0

public interface ServletContainerInitializer {

public void onStartup(Set<Class<?>> c, ServletContext ctx)

throws ServletException;

}

查看此接口的注释

<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.

大概意思是讲必须在该接口所在项目的META-INF/services/文件夹下生成一个文件名字为javax.serlvet.ServletContainerInitializer的文件，内容要与ServletContainerInitializer接口的实现类的全路径一样才能被发现。

仔细看spring-web包下有类似的结构。声明为了javax.servlet.ServletContainerInitializer的文件，内容为 org.springframework.web.SpringServletContainerInitializer

从springmvc启动日志学习

日志来自于实现类：SpringServletContainerInitializer上一段源码：

@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);
		}
	}

因为没有使用基于servlet3.0规范的类，所以有这一条日志。