在spring中可以通过代码的方式配置原来的xml文件.在用java 代码配置web.xml时候,spring文档说配置类要实现WebApplicationInitializer接口.关于为什么要实现org.springframework.web.WebApplicationInitializer接口,记录下.

其实是对servlet规范的一种使用.servlet早就支持用代码实现相关的xml配置.

servlet相关接口:

    @HandlesTypes:

    解释:实现了ServletContainerInitializer 接口的类在web程序启动的时候会被容器扫描加载并且调用其onStartup方法(在方法中注册servlet或者filters等web.xml中会进行的配置).但是实现此接口的类必须在某个jar包中的META-INF/services路径下进行声明(java spi).spring 中的实现类为org.springframework.web.SpringServletContainerInitializer,该类在springweb jar包中声明:

@HandlesTypes(WebApplicationInitializer.class)public class SpringServletContainerInitializer implements ServletContainerInitializer {	@Override	public void onStartup(Set
    
     > webAppInitializerClasses, ServletContext servletContext)			throws ServletException {		List
     
       initializers = new LinkedList
      
       ();		if (webAppInitializerClasses != null) {			for (Class
        waiClass : webAppInitializerClasses) {				// Be defensive: Some servlet containers provide us with invalid classes,				// no matter what @HandlesTypes says...				if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&						WebApplicationInitializer.class.isAssignableFrom(waiClass)) {					try {						initializers.add((WebApplicationInitializer) waiClass.newInstance());					}					catch (Throwable ex) {						throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);					}				}			}		}		if (initializers.isEmpty()) {			servletContext.log("No Spring WebApplicationInitializer types detected on classpath");			return;		}		servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");		AnnotationAwareOrderComparator.sort(initializers);		for (WebApplicationInitializer initializer : initializers) {			initializer.onStartup(servletContext);		}	}}
      
     
    

SpringServletContainerInitializer上的注解:@HandlesTypes(WebApplicationInitializer.class)

意思是向该类注入HandlesTypes指定的类或者实现该接口的类.所以我们一般实现WebApplicationInitializer,通过代码注册servlet就可以使用了.

所以流程是spring 中的SpringServletContainerInitializer onStartup()方法被容器调用,然后onStartup()方法最终调用的是我们实现类中的方法.

参考servlet3.1规范

      spring-framework-reference

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增加篇文章:http://stefan-isele.logdown.com/posts/201646  (2017年11月10日10:35:44)