During a two-month period, Lucky Zhang enhanced authentication and concurrency mechanisms in Java-based backend systems. In the spring-framework repository, Lucky refactored the ResponseBodyEmitter to use AtomicBoolean for thread-safe signaling, addressing race conditions in concurrent streaming and improving endpoint reliability. For alibaba/nacos, Lucky implemented automatic token refresh and re-login logic, ensuring seamless client access by handling 403 responses and managing retry attempts. Additionally, Lucky introduced randomized token refresh windows to distribute login traffic, reducing server load and improving scalability during peak usage. These contributions demonstrated depth in Java, Spring Framework, and server management, resulting in more robust and maintainable systems.