Custom exception classes in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a custom exception is thrown in a Spring Boot REST controller?

Consider a Spring Boot REST controller that throws a custom exception ResourceNotFoundException when a resource is missing. What will the client receive if no global exception handler is defined?

Spring Boot

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

@RestController
public class MyController {
    @GetMapping("/item/{id}")
    public String getItem(@PathVariable String id) {
        throw new ResourceNotFoundException("Item not found");
    }
}

A The client receives a 500 Internal Server Error with a default error page.

B The client receives a 404 Not Found status with the exception message in the response body.

C The client receives a 400 Bad Request status with a JSON error message.

D The client receives a 200 OK status with an empty response body.

💡 Hint

Think about what Spring Boot does by default when an exception is thrown and no handler is present.

Without a global or controller-specific exception handler, Spring Boot treats uncaught exceptions as server errors and returns a 500 status with a default error page.

📝 Syntax

intermediate

Which custom exception class definition is syntactically correct in Spring Boot?

Choose the correct way to define a custom unchecked exception class named InvalidInputException that accepts a message.

A

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

B

public class InvalidInputException extends Exception {
    public InvalidInputException(String message) {
        super(message);
    }
}

C

public class InvalidInputException {
    public InvalidInputException(String message) {
        super(message);
    }
}

D

public class InvalidInputException extends Throwable {
    public InvalidInputException(String message) {
        super(message);
    }
}

💡 Hint

Remember that unchecked exceptions extend RuntimeException.

Custom unchecked exceptions should extend RuntimeException. Option A extends Exception which is checked, C does not extend any class, and D extends Throwable which is not recommended.

🔧 Debug

advanced

Why does this custom exception handler not catch the exception?

Given the following code, why does the handleCustomException method not handle MyCustomException?

Spring Boot

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

@RestController
public class DemoController {
    @GetMapping("/test")
    public String test() {
        throw new MyCustomException("Error occurred");
    }
}

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(IllegalArgumentException.class)
    public ResponseEntity<String> handleCustomException(IllegalArgumentException ex) {
        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(ex.getMessage());
    }
}

A Because @ControllerAdvice is missing @RestController annotation.

B Because the handler listens for IllegalArgumentException, not MyCustomException.

C Because MyCustomException must extend Exception, not RuntimeException.

D Because the handler method must return void to catch exceptions.

💡 Hint

Check the exception type specified in the @ExceptionHandler annotation.

The handler method is set to catch IllegalArgumentException, but the thrown exception is MyCustomException, so it is not caught.

❓ state_output

advanced

What is the HTTP status code returned by this custom exception handler?

Given this custom exception and handler, what HTTP status code will the client receive when DataConflictException is thrown?

Spring Boot

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

@ControllerAdvice
public class ApiExceptionHandler {
    @ExceptionHandler(DataConflictException.class)
    public ResponseEntity<String> handleConflict(DataConflictException ex) {
        return ResponseEntity.status(HttpStatus.CONFLICT).body(ex.getMessage());
    }
}

A 200 OK

B 404 Not Found

C 500 Internal Server Error

D 409 Conflict

💡 Hint

Look at the status code used in the ResponseEntity.

The handler returns a ResponseEntity with status HttpStatus.CONFLICT, which corresponds to 409.

🧠 Conceptual

expert

Why use custom exception classes in Spring Boot applications?

Which of the following is the best reason to create custom exception classes in a Spring Boot app?

A To avoid using try-catch blocks anywhere in the code.

B To reduce the size of the application by replacing all exceptions with one class.

C To provide specific error types that can be handled separately and return meaningful HTTP responses.

D To automatically log all errors without additional configuration.

💡 Hint

Think about how custom exceptions improve error handling and client communication.

Custom exceptions allow precise identification of error causes and enable tailored HTTP responses, improving API clarity and client experience.