Recent research showed that the majority of compatibility-breaking changes in a component-based, object-oriented software system are refactorings [5]. The software updating process in such system with the presence of heavily refactored application programming interface (API) is largely manual and disruptive to running, mission-critical applications, which are expected to run continuously without any interruptions. To address the online, API update issue for mission-critical systems, we have developed an online updating framework based on Virtual Execution Environment (VEE) such as Java Virtual Machine. The framework extends the VEE to take the API change log, which records changes to API components, and seamlessly apply proper updates to the running system without human intervention and without shutting down the system. This framework was implemented as an extension to Jikes Research Virtual Machine. Our experimental study showed that our online update tool requires little overhead while maintaining the consistent state of the updated running application.