From Ancient to Cutting-Edge: I Modernized a Full-Stack Monorepo with Cursor AI

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Every seasoned developer has a project in their closet, a digital skeleton of sorts. Mine was a fullstack monorepo sample application, a relic from the past built with Java 8, Angular 5, and MongoDB. It was functional, but its tech stack was gathering dust. A manual upgrade would have meant weeks of dependency hell, breaking changes, and configuration nightmares.

Instead, I decided to pair up with an AI tool, Cursor, to see if it could breathe new life into this old codebase. The results were nothing short of astounding.

The Challenge: A Complete Stack Overhaul

The mission was clear: drag this application into the present day. This wasn’t just about updating a few libraries. It required a fullstack modernization:

  • Java Backend: From Java 8 to Java 21.

  • Angular Frontend: A huge leap from Angular 5 to Angular 17.

  • API Layer: Refactor legacy JAX-RS APIs.

  • Deployment: Update configurations for Tomcat 10.

This is the kind of project that typically gets pushed to the back of the backlog indefinitely. But with Cursor, it became a fascinating exercise in AI-assisted development.

Step 1: Conquering the Dependency Mountain

The first and most daunting task was updating dependencies. Anyone who has manually updated a pom.xml and package.json across major versions knows the pain. I simply instructed Cursor to analyze the project and update everything to the latest stable versions.

It didn’t just blindly change version numbers. Cursor understood the dependencies between libraries, identified breaking changes, and suggested compatible versions. It seamlessly transitioned the project from Java 8 to 21 and Angular 5 to 17, saving what would have been at least a few days of tedious, error-prone work.

Step 2: Intelligent API Refactoring

The original Java backend used older JAX-RS standards for its APIs. With Java 21 and modern Jakarta EE, much of the boilerplate and implementation patterns had changed.

I tasked Cursor with refactoring the entire API layer. It intelligently rewrote the JAX-RS endpoints, updated method signatures, and adapted the code to modern best practices. It wasn’t just a find-and-replace; it understood the intent of the code and modernized it accordingly. Then, on the other side, I had it refactor the Angular services to consume these newly updated APIs, ensuring the contract between the front and back end remained intact.

Step 3: Untangling the Configuration Web

One of the biggest headaches in a Java web app migration is the deployment descriptor (web.xml). Migrating to Tomcat 10 means moving from javax.* to the jakarta.* namespace. This is a tedious, manual process that’s easy to get wrong.

Cursor handled it flawlessly. I prompted it to update the web.xml for Tomcat 10, specifically for CDI and Jersey servlet configurations. It correctly updated the namespaces, class paths, and servlet definitions in minutes.

Step 4: The Final Mile - Build and Deploy

With the code fully modernized, the final test was to see it run. Cursor’s assistance didn’t stop at the code. I used it to:

  1. Generate setup commands to install the correct versions of Tomcat 10 and MongoDB.

  2. Build the .war file using the updated Maven configuration.

  3. Deploy the application to the local Tomcat server.

And just like that, it worked. The application, now running a completely modern stack, loaded up in the browser perfectly. The entire process, from a dusty legacy app to a fully functional modern one, was completed in a fraction of the time it would have taken manually.

My Takeaway: This is More Than a Copilot

Using Cursor for this project felt less like using an assistant and more like pair programming with a seasoned expert who happens to work at lightning speed. It excelled at understanding the full context of a monorepo from the database to the deployment script. And handled the most tedious parts of software modernization with ease.

If you have a legacy project sitting on the shelf, don’t let the fear of a painful migration hold you back. Tools like Cursor have fundamentally changed the game, turning daunting refactoring projects into exciting opportunities for innovation.