springboot 2.1.3.RELEASE添加filter,servlet源码学习

Servlet规范中，通过ServeltContext来注册Filter、Servlet，这里分析Filter，Servlet是相同逻辑

springboot2.0中，我们通过

FilterRegistrationBean将指定得filter来实现ServeltContext注册filter

 
           FilterRegistrationBean的实例化过程 
          
           public  
           FilterRegistrationBean(T filter, ServletRegistrationBean... servletRegistrationBeans) { 
          
           super 
           (servletRegistrationBeans); 
          
           Assert.notNull(filter,  
           "Filter must not be null" 
           ); 
          
           this 
           .filter = filter; 
          
           } 
          
           super 
           的实例化 
          
           AbstractFilterRegistrationBean(ServletRegistrationBean... servletRegistrationBeans) { 
          
           Assert.notNull(servletRegistrationBeans,  
           "ServletRegistrationBeans must not be null" 
           ); 
          
           Collections.addAll( 
           this 
           .servletRegistrationBeans, servletRegistrationBeans); 
          
           }

可知FilterRegistrationBean得实例化过程就是将Filter保存到servletRegistrationBeans（一个set）中

再分析FilterRegistrationBean类

FilterRegistrationBean的父类是一个ServletContextInitializer，他有一个方法onStartup(ServletContext servletContext)

其结果最终会调用

servletContext.addFilter(this.getOrDeduceName(filter), filter)

现在看看ServletContextInitializer.onStartup的调用地方

 
           springboot启动 
          
           new  
           SpringApplication(XXApplication. 
           class 
           ).run(XXApplication. 
           class 
           ,args) 
          
           调用 
          
           refreshContext(context); -> refresh(context); -> ((AbstractApplicationContext) applicationContext).refresh(); 
          
           -> ServletWebServerApplicationContext.onRefresh(); -> createWebServer(); 
          
           WebServer webServer =  
           this 
           .webServer; 
          
           ServletContext servletContext = getServletContext(); 
          
           if  
           (webServer ==  
           null  
           && servletContext ==  
           null 
           ) { 
          
           ServletWebServerFactory factory = getWebServerFactory(); 
          
           this 
           .webServer = factory.getWebServer(getSelfInitializer()); 
          
           }

再分析getSelfInitializer方法

 
           prepareWebApplicationContext(servletContext); 
          
           registerApplicationScope(servletContext); 
          
           WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(),servletContext); 
          
           for  
           (ServletContextInitializer beans :getServletContextInitializerBeans()) {　　　　　　　　　　　　　　 
          
                  //调用ServletContextInitializer的onStartup方法

 
           beans.onStartup(servletContext); } 
          
           -> getServletContextInitializerBeans()

 
           ->  
           new  
           ServletContextInitializerBeans(getBeanFactory()) 
          
           -> addAdaptableBeans(beanFactory)

 
           addAdaptableBeans(ListableBeanFactory beanFactory) 代码如下： 
          
           MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory); 
          
           //将servlet类的bean包装为ServletRegistrationBean 
          
           addAsRegistrationBean(beanFactory, Servlet. 
           class 
           , 
           new  
           ServletRegistrationBeanAdapter(multipartConfig)); 
          
           //将Filter的bean包装为FilterRegistrationBean 
          
           addAsRegistrationBean(beanFactory, Filter. 
           class 
           , 
           new  
           FilterRegistrationBeanAdapter()); 
          
           for  
           (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes())  
          
           {       　　 
          
           addAsRegistrationBean(beanFactory, EventListener. 
           class 
           ,(Class<EventListener>) listenerType, 
           new  
           ServletListenerRegistrationBeanAdapter()); 
          
           }

这里提一下，如果Servlet的bean实例名为dispatcherServlet，且该实例在seen集合中（seen集合为自定义配置的实例，通过ServletContextInitializerBeans.addServletContextInitializerBean入口可以查看源码），则设置默认值为 /

 
           String url = (totalNumberOfSourceBeans !=  
           1 
           ) ?  
           "/"  
           + name +  
           "/"  
           :  
           "/" 
           ; 
          
           if  
           (name.equals(DISPATCHER_SERVLET_NAME)) { 
          
           url =  
           "/" 
           ;  
           // always map the main dispatcherServlet to "/" 
          
           } 
          
           ServletRegistrationBean<Servlet> bean =  
           new  
           ServletRegistrationBean<>(source,url);   
          
           bean.setName(name); 
          
           bean.setMultipartConfig( 
           this 
           .multipartConfig); 
          
           return  
           bean;

总结：springboot启动时，会将所有的 FilterRegistrationBean、ServletRegistrationBean以及被spring管理的Servlet和Filter的实例，通过　　　　 ServletContext注册Servlet以及Filter