As Internet provides an open and dynamic runtime environment for distributed applications, one of the most important challenges to the next generation of middleware is how to allow the observation and manipulation of the runtime states and behaviors internal of middleware platform. Reflective middleware is able to open up the platform implementation to meet such requirements. There are three limitations in current research and experiments on reflective middleware: they focus on parts or individual entity of a system, lacking a global view; they only address the reflection of the underlying platform, ignoring the reflection of the application; they mostly experiment on CORBA with less work on J2EE. The design and implementation of a reflective component operating platform, called PKUAS, is presented. Based on its componentized structure, PKUAS introduces software architecture as the global view of the whole reflective system. As a J2EE-compliant application server, PKUAS can reflect both the underlying platform and EJB components. Moreover, this paper demonstrates the usage of reflection with the PKUAS management tool and evaluates PKUAS through comparison with other reflective middlewares. The work presented in this paper addresses the aforementioned limitations and improves the applicability of reflective middleware.