Spring文档阅读之Web on Servlet Stack

1.Spring Web MVC

Spring MVC是基于Servlet API开发的原生web框架，其名字来源于在Spring项目的模块名称（spring-webmvc）。

Spring还推出了基于reactive栈的web框架 Spring WebFlux。
Parallel to Spring Web MVC, Spring Framework 5.0 introduced a reactive-stack web framework whose name, “Spring WebFlux,” is also based on its source module (spring-webflux). This section covers Spring Web MVC. The next section covers Spring WebFlux.

1.1. DispatcherServlet

Spring MVC围绕一个Servlet（DispatcherServlet）设计，提供对于不同请求的分享算法，实际的工作由框架配置的组件完成。

DispatcherServlet需要通过Java代码或者web.xml进行配置，同时DispatcherServlet通过Sprong配置来发现业务组如请求路由匹配，视图解析器，异常处理等等。

以下代码示范了如何通过代码注册并初始化一个DispatcherServlet，它会被Servlet容器自动检测到：

public class MyWebApplicationInitializer implements WebApplicationInitializer {

@Override
public void onStartup(ServletContext servletCxt) {

    // Load Spring web application configuration
    AnnotationConfigWebApplicationContext ac = new AnnotationConfigWebApplicationContext();
   // You need a Spring context configuration class name APPConfig.class
    ac.register(AppConfig.class);
    ac.refresh();

    // Create and register the DispatcherServlet
    DispatcherServlet servlet = new DispatcherServlet(ac);
    ServletRegistration.Dynamic registration = servletCxt.addServlet("app", servlet);
    registration.setLoadOnStartup(1);
    registration.addMapping("/app/*");
}

}
可以使用web.xml配置DispatcherServlet：

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

<context-param>
    <param-name>contextConfigLocation</param-name>
    <!-- you need a Spring context configuration file name app-context.xml -->
    <param-value>/WEB-INF/app-context.xml</param-value>
</context-param>

<servlet>
    <servlet-name>app</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value></param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>app</servlet-name>
    <url-pattern>/app/*</url-pattern>
</servlet-mapping>