Building a declarative API with Spring AOP and SpEL

Wed, 12 Feb 2025 15:57:11 +0000

In this article, we’ll implement a declarative API to perform tasks belonging to cross-cutting concerns, using auditing as an example. We’ll see how SpEL and Spring AOP allow us to easily intercept invocations throughout a code base and perform arbitrary logic in an expressive and non-invasive manner.

A story about legacy

Let’s pretend that we inherited a legacy system. The system is in a dismal state, with every change always at risk of bringing the whole thing down. One day, there is a business requirement to audit a few dozen methods scattered throughout the code base. After every invocation of these methods, we should notify an external system by sending a client id and an operation (1234, "CREATE_USER").

Who instruments the instrumenters?

Thu, 30 May 2024 16:25:45 +0000

Have you ever wondered how libraries like Spring and Mockito modify your code at run-time to implement all their advanced features?

Wouldn’t it be cool to get a peek behind the curtains?

This is the premise of my meta-agent , a Java agent to instrument instrumenters, to get these insights and what this blog post is about.

This article is a collaboration with Mikaël Francoeur , who had the idea for the meta-agent and wrote most of this post. So it’s my first ever post-collaboration. But I start with a short introduction to the agent itself before Mikaël takes over with real-world examples.

Mikael Francoeur on foojay.io - Friends of OpenJDK

Building a declarative API with Spring AOP and SpEL

A story about legacy

Who instruments the instrumenters?