🚫 Stop Writing Fat Controllers: Follow the Controller-Service-Repository Pattern

In a typical Spring Boot project, it’s easy to let your controller classes grow out of control. You start by handling a simple request, then add a bit of business logic, maybe some database access — and before you know it, your controller has become a bloated, untestable mess.

If your controller methods are more than 10–15 lines, or if they contain database logic, conditionals, and exception handling — you’re likely writing a fat controller.

The solution? Follow the Controller-Service-Repository (CSR) pattern — a clean and proven way to structure Spring Boot applications that keeps your code readable, testable, and maintainable.

💣 What’s a Fat Controller?

A “fat controller” refers to a controller class that does too much:

• Handles request mapping
• Contains business logic
• Talks to the database
• Manages error handling
• Performs input validation
• Builds complex response objects