How Spring Uses JDK and CGLIB Proxies to Power Transactions and Caching

Spring annotations like @Transactional and @Cacheable work by inserting a proxy object between the caller and the actual bean, adding behaviour without modifying the original code. This proxy pattern mirrors a classic design where a wrapper class implements the same interface as the real object, forwarding calls while injecting extra logic. Spring builds these proxies automatically at runtime using one of two mechanisms: JDK dynamic proxies, which work via Java's built-in Proxy API and require an interface, or CGLIB proxies, which subclass the target class directly and work without interfaces. The choice between them affects how Spring-managed concerns like transactions, caching, security, and async execution are applied across an application. Understanding how proxies are constructed helps developers avoid common pitfalls, such as self-invocation bypassing proxy logic or final classes breaking CGLIB subclassing.