Due to the dynamic and ephemeral nature of ubiquitous computing (ubicomp) environments, it is necessary that application software in ubicomp environments is situation-aware (SA) and should be adaptable to both users? situation changes and the requirement changes. Reconfigurable Context-Sensitive Middleware (RCSM) has been developed to provide development and runtime support for SA software in ubicomp environments, but do not provide runtime support for on-demand context acquisition, action scheduling and dynamic reconfiguration of SA software, and development support that maximize the reusability. In this paper, the development and runtime support provided by RCSM have been substantially expanded to greatly simplify the development of situation-aware application software, and to achieve reusability and runtime reconfigurability simultaneously.