前言

在Spring Xml和JavaConfig一文中曾经使用实现WebApplicationInitializer的方式举例过, 但未对其进行特殊说明, 这里补充一下:

1. 一个应用中可以有多个WebApplicationInitializer实例, 但加载顺序不定
2. 可以使用抽象类继承WebApplicationInitializer的方式预置一些逻辑
3. Spring提供了一些抽象启动类, 默认注册了名为dispatcher的Servlet, UML如下:
   
   然后暴露抽象方法用于注册Spring Context.
4. Spring只提供了注解方式的初始化抽象类, 我们可以仿照其编写XML方式的初始化抽象类:

   import org.springframework.web.WebApplicationInitializer;
   import org.springframework.web.context.support.XmlWebApplicationContext;
   import org.springframework.web.servlet.DispatcherServlet;import javax.servlet.ServletContext;
   import javax.servlet.ServletRegistration;public abstract class AbstractXmlWebAppInitializer implements WebApplicationInitializer {@Overridepublic void onStartup(ServletContext container) {XmlWebApplicationContext context = new XmlWebApplicationContext();context.setConfigLocation(getConfigLocation());context.setConfigLocations(getConfigLocations());ServletRegistration.Dynamic dispatcher = container.addServlet("dispatcher", new DispatcherServlet(context));dispatcher.setLoadOnStartup(1);dispatcher.addMapping("/");}protected abstract String getConfigLocation();protected abstract String[] getConfigLocations();
   }
   

5. 如果项目之前是通过web.xml方式配置, 而又须要在其基础上进行增强配置, 比如开启异步请求支持, 可以这样:

   import org.springframework.web.WebApplicationInitializer;import javax.servlet.ServletContext;
   import javax.servlet.ServletRegistration;import static org.springframework.web.servlet.support.AbstractDispatcherServletInitializer.DEFAULT_SERVLET_NAME;public class MyWebAppInitializer implements WebApplicationInitializer {@Overridepublic void onStartup(ServletContext container) {ServletRegistration servletRegistration = container.getServletRegistration(DEFAULT_SERVLET_NAME);if (servletRegistration instanceof ServletRegistration.Dynamic) {((ServletRegistration.Dynamic) servletRegistration).setAsyncSupported(true);}}
   }