基于 Java 的配置在 Spring MVC 中究竟是如何工作的

Question

I have no trouble in understanding how XML-based configuration works with Spring MVC. There is a standard file ("web.xml") in a standard directory ("WEB-INF/"). How does a server knows that this class is responsible for front-servlet initialization though?

public class DispatcherServletInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[] { RootApplicationContextConfig.class };
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class[] { WebApplicationContextConfig.class };
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }
}

Looking at this file, I can easily understand that a server will load the servlet on startup with the highest priority.

<servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>
        org.springframework.web.servlet.DispatcherServlet
    </servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/spring/dispatcher-config.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

Answer 1

Since Servlet specification 3.0 you can use web.xml or annotations to configure servlets, and with the annotation based configuration additional mechanisms were included to make web.xml unnecessary. I'm not sure if there are cases where web.xml is still useful, I can't remember touching one in years.

SpringServletContainerInitializer class implements the javax.servlet.ServletContainerInitializer which is the starting point for the servlet container (eg Tomcat) to set things up.