MethodInterceptor

MethodInterceptor is a component used in aspect-oriented programming to intercept method calls on an object and apply additional behavior before, after, or instead of the original method execution. It is commonly implemented via a dynamic proxy or bytecode weaving and is designed to encapsulate cross-cutting concerns, such as logging, security, transactions, or caching, in a reusable way.

Typically, a MethodInterceptor exposes a single method that receives an invocation context. The context provides access to the target object, the method being invoked, and its arguments, and it offers a mechanism to proceed to the next step in the chain. The interceptor can inspect or modify the invocation data, and it can choose to call proceed() to invoke the underlying method, or return a value immediately to short-circuit the call. When multiple interceptors are chained, each can perform its work around the invocation, with control passing through the chain in order.

In Java, the concept is common in the AOP ecosystem. The AOP Alliance defines a MethodInterceptor interface, and frameworks such as Spring AOP use it to implement advisors and advice. Other ecosystems offer analogous constructs, such as interceptors in dynamic proxy libraries. Practical uses include logging wrappers, security checks, transaction demarcation, and result caching or retry policies.

Limitations include potential performance overhead, complexity in debugging, and the need for well-defined invocation semantics to avoid altering application behavior unexpectedly.