Error Handling & Advice
Learn error handling patterns and use @ControllerAdvice in Spring Boot.
Error Handling & Advice is a free Java Academy lesson on CoddyKit — lesson 3 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro
Error handling improves user experience. Instead of raw stack traces, return meaningful messages.
Code: Custom exception
Create a custom exception for missing resources.
public class UserNotFoundException extends RuntimeException {
public UserNotFoundException(Long id) {
super("User not found with id " + id);
}
}
Code: Throw exception
Service throws UserNotFoundException if no user is found.
public User find(Long id) {
return repo.findById(id)
.orElseThrow(() -> new UserNotFoundException(id));
}
Code: ControllerAdvice
@ControllerAdvice catches exceptions and maps them to responses.
import org.springframework.web.bind.annotation.*;@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(UserNotFoundException.class)
@ResponseBody
public String handleNotFound(UserNotFoundException ex) {
return ex.getMessage();
}
}
Benefits
Central handling avoids duplication and ensures consistent error messages across APIs.
Usage
Test with GET /users/999. You should see "User not found with id 999" instead of a stack trace.
ControllerAdvice check
Quick check: What does @ControllerAdvice provide in Spring Boot?
Recap
Recap: Created custom exception, threw it in service, handled with @ControllerAdvice, and returned clear messages.
Frequently asked questions
Is the “Error Handling & Advice” lesson free?
Yes — the full text of “Error Handling & Advice” is free to read here on the web, and the Java Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO.
What will I learn in “Error Handling & Advice”?
Learn error handling patterns and use @ControllerAdvice in Spring Boot. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Java Academy?
No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Error Handling & Advice” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Java Academy lesson?
Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- JPA/H2 & Repositories
- CRUD Service Layers
- Error Handling & Advice