It is the proxy pattern that made Spring AOP able to decouple crosscutting concerns from the core application's business logic or functionalities. The proxy pattern is a structural design pattern included in a book by the Gang of Four (GoF). In practice, the proxy pattern creates different object wrapping out of an original object without changing the behavior of the original object to allow intercepting its method call, and the outside world would feel they are interacting with the original object and not a proxy.