Spring文檔閱讀之Web on Servlet Stack

1.Spring Web MVC

Spring MVC是基於Servlet API開發的原生web框架，其名字來源於在Spring項目的模塊名稱（spring-webmvc）。

Spring還推出了基於reactive棧的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圍繞一個Servlet（DispatcherServlet）設計，提供對於不一樣請求的分享算法，實際的工做由框架配置的組件完成。

DispatcherServlet須要經過Java代碼或者web.xml進行配置，同時DispatcherServlet經過Sprong配置來發現業務組如請求路由匹配，視圖解析器，異常處理等等。

如下代碼示範瞭如何經過代碼註冊並初始化一個DispatcherServlet，它會被Servlet容器自動檢測到：

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>