Java Academy · Lesson

Error Handling & Advice

Learn error handling patterns and use @ControllerAdvice in Spring Boot.

Lesson 3 of 38 steps

Error Handling & Advice is a free Java Academy lesson on CoddyKit. This is 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, and your progress syncs across the web and the CoddyKit app. The Java Academy course includes 3 lessons in total.

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?

Answer it in the interactive lesson

Recap

Recap: Created custom exception, threw it in service, handled with @ControllerAdvice, and returned clear messages.

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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. 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. The Java Academy course includes 3 lessons in total.

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, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 3.

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.

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