Log Instrumentation Tool Using AOP and Javassist for Interface Parameter and Performance Monitoring

In the testing process, developers often face a lack of sufficient test cases, difficulty constructing diverse data scenarios, uncertainty about downstream service responses, and the need for continuous performance monitoring; these challenges motivated the creation of a log instrumentation tool that operates without altering existing business logic.

The tool is transparent to both upstream and downstream services and is built on the Aspect‑Oriented Programming (AOP) concept, using the Javassist library to weave proxies into target interfaces. It captures request parameters, response data, and performance metrics, storing them in logs and a database.

A brief terminology overview explains that AOP (Aspect‑Oriented Programming) allows cross‑cutting concerns such as logging and permission checks to be modularized separately from core business logic, unlike traditional OOP. Javassist is chosen over ASM because it enables bytecode manipulation directly through Java code, offering a lower learning curve while still allowing class creation and modification.

The instrumentation process works at the interface level: reflection identifies the target interfaces, a proxy class is generated and injected, the original method is renamed, and the proxy forwards calls while recording inputs, outputs, and timing information. This proxy is invisible to callers, preserving the original API contract.

Collected data serves multiple purposes: input parameters can be used to enrich test case libraries; output data enables accurate mocking of services; and performance statistics allow long‑term trend analysis, alerting, and root‑cause investigation when latency spikes occur.