实现WebApplicationinitializer的类都可以在web应用程序启动时被加载。
这个是通过SpringServletContainerIntializer实现ServletContainerIntializer实现的。

首先建个WebApplicationInitializer.java

package com.boventech.config;  
import javax.servlet.ServletContext;  
import javax.servlet.ServletException;  
/** 
 * WebApplicationInitializer接口 
 * @author hu.sun 
 */  
public interface WebApplicationInitializer{  
    public  void config(ServletContext context) throws ServletException;  
}  

继续，由于必须通过SpringServletContailnerIntializer才能加载，再建个SpringServletContailnerIntializer类：

package com.boventech.config;  
import java.lang.reflect.Modifier;  
import java.util.Set;  
import javax.servlet.ServletContainerInitializer;  
import javax.servlet.ServletContext;  
import javax.servlet.ServletException;  
import javax.servlet.annotation.HandlesTypes;  
  
@HandlesTypes(WebApplicationInitializer.class)    
public class SpringServletContainerInitializer implements ServletContainerInitializer{  
    @Override  
    public void onStartup(Set<Class<?>> webApplicationInitializers, ServletContext servletContext)  
            throws ServletException {  
        if (webApplicationInitializers != null) {  
            for (Class<?> webApplicationInitializerClass : webApplicationInitializers) {  
                if (!webApplicationInitializerClass.isInterface() && !Modifier.isAbstract(webApplicationInitializerClass.getModifiers()) &&  
                        WebApplicationInitializer.class.isAssignableFrom(webApplicationInitializerClass)) {  
                    try {  
                        ((WebApplicationInitializer) webApplicationInitializerClass.newInstance()).config(servletContext);  
                    }  
                    catch (Throwable ex) {  
                        throw new ServletException("Failed to instantiate webApplicationInitializer class", ex);  
                    }  
                }  
            }  
        }  
    }  
}  

注意：
要实现ServletContainerInitializer接口，必须指定实现的类。@HandlesTypes就起到关键性作用。
还有一个最重要的：在Libraries->Spring -web-x.x.x.jar->META-INF/services/javax.servlet.ServletContainerInitializer里面的内容必须是实现ServletContainerInitializer的类，即com.boventech.config.SpringServletContainerInitializer。

package com.boventech.config;  
  
import javax.servlet.ServletContext;  
import javax.servlet.ServletException;  
  
import org.springframework.web.context.ContextLoaderListener;  
import org.springframework.web.util.WebAppRootListener;  
  
public class DefaultServletConfig implements WebApplicationInitializer{  
  
    @Override  
    public void config(ServletContext servletContext)  throws ServletException{  
        servletContext.addListener(new ContextLoaderListener());  
        servletContext.addListener(new WebAppRootListener());  
        servletContext.setInitParameter("contextConfigLocation", "classpath*:**/*Context.xml");  
        //设置webAppRootKey得值以得到根目录  
        servletContext.setInitParameter("webAppRootKey", "learning");  
    }  
}