Web application servers (WASs) are middleware platforms for deployment and execution of component-based web applications. To cater for an increasingly diverse range of QoS demands, WAS must be capable of adaptation during execution to modify itself and to respond to changing conditions in its external environment. To accommodate such changes, WAS should provide both deployment-time configurability and run-time reconfigurability. Unfortunately, most of the mainstream web application servers adopt a monolithic architecture and "black box" philosophy to their design, and fail to properly address such requirements. In our point of view, adaptation and reconfigurability of WASs should be available at any time of the whole lifecycle. In this paper, a middleware architecture (WebFrame) that supports multi-phase adaptation using computational reflection, microkernel, and component techniques is proposed for web application servers. The architecture is structured into five layers. Both deployment-time configuration and run-time reconfiguration at multiple layers is supported in this architecture. The key insight to this work is the MService Reconfiguration design pattern, which provides dynamic adaptation at run time by swapping in/out the optional middleware components. The comparative evaluation of the performance impact of reflection and multi-phase reconfigurability on systems are given.