A system, method and program enabling users to diagnose applications easily without affecting the operating performance of the application server, optimizing the log mechanism based on the integrated development environment. The method includes running the application in a main running environment and at least one shadow environment, the shadow environment obtained by duplicating the main running environment; and the main running environment interacting with the shadow environment with respect to the fault of the application. The method includes performing the steps of the main running environment: monitoring the exceptions in the system and sending system exception information to the shadow environment in the event of finding exceptions in the system. The shadow environment: receives the system exception information, opens diagnostic log/trace functions to obtain diagnosis log/trace files related to the system exceptions, and analyzes the diagnosis result based on the obtained diagnosis log/trace files.