Why centralized error handling matters in Spring Boot - See It in Action

Why Centralized Error Handling Matters in Spring Boot

📖 Scenario: You are building a simple Spring Boot web application that manages user profiles. You want to make sure that when errors happen, your app handles them in one place so it is easier to maintain and users get clear messages.

🎯 Goal: Build a Spring Boot project that shows how to centralize error handling using @ControllerAdvice and @ExceptionHandler. This will catch errors from any controller and return a friendly message.

📋 What You'll Learn

Create a custom exception class called UserNotFoundException.

Create a controller class called UserController with a method that throws UserNotFoundException.

Create a centralized error handler class called GlobalExceptionHandler using @ControllerAdvice.

Add a method in GlobalExceptionHandler annotated with @ExceptionHandler(UserNotFoundException.class) to handle the exception and return a custom response.

💡 Why This Matters

🌍 Real World

Centralized error handling is used in real web applications to manage errors in one place, making maintenance easier and improving user experience by providing consistent error messages.

💼 Career

Understanding centralized error handling is important for backend developers working with Spring Boot or similar frameworks, as it is a common pattern in professional web development.

1

Create the custom exception class

Create a public class called UserNotFoundException that extends RuntimeException. Add a constructor that accepts a String message and passes it to the superclass.

Spring Boot

// Your code here

Need a hint?

Think of this class as a special kind of error that you can throw when a user is not found.

2

Create the UserController with a method that throws the exception

Create a class called UserController annotated with @RestController. Add a method getUserById that takes a Long id parameter and throws new UserNotFoundException("User not found").

Spring Boot

public class UserNotFoundException extends RuntimeException {
    public UserNotFoundException(String message) {
        super(message);
    }
}

// Your code here

Need a hint?

This controller simulates a user lookup that always fails by throwing your custom exception.

3

Create the GlobalExceptionHandler class with @ControllerAdvice

Create a class called GlobalExceptionHandler annotated with @ControllerAdvice. This class will hold methods to handle exceptions globally.

Spring Boot

public class UserNotFoundException extends RuntimeException {
    public UserNotFoundException(String message) {
        super(message);
    }
}

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {
    @GetMapping("/users/{id}")
    public String getUserById(@PathVariable Long id) {
        throw new UserNotFoundException("User not found");
    }
}

// Your code here

Need a hint?

This class will catch exceptions from all controllers in one place.

4

Add an @ExceptionHandler method for UserNotFoundException

Inside GlobalExceptionHandler, add a method handleUserNotFoundException annotated with @ExceptionHandler(UserNotFoundException.class). It should accept a UserNotFoundException parameter and return a String with the exception message.

Spring Boot

public class UserNotFoundException extends RuntimeException {
    public UserNotFoundException(String message) {
        super(message);
    }
}

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;

@RestController
public class UserController {
    @GetMapping("/users/{id}")
    public String getUserById(@PathVariable Long id) {
        throw new UserNotFoundException("User not found");
    }
}

@ControllerAdvice
public class GlobalExceptionHandler {
    // Your code here
}

Need a hint?

This method catches the exception and returns its message as the response.