对外:SecurityContextPersistenceFilter,SecurityContextRegister(HttpSessionSecurityContextRepository),HttpSession,SecurityContext,Authentication
说明:SecurityContextPersistenceFilter的作用是请求开始之前从HttpSession获取SecurityContext;请求结束把SessionContext存储在HttpSession
对内:SecurityContextHolder,SecurityContextHolderStrategy,SecurityContext,Authentication
SecurityContextHolder相当于一个委派类,具体操作委派给SecurityContextHolderStrategy的实现类。