Handling not found exceptions in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a custom exception class named ResourceNotFoundException.

Spring Boot

public class ResourceNotFoundException extends [1] {
    public ResourceNotFoundException(String message) {
        super(message);
    }
}

Drag options to blanks, or click blank then click option'

AThrowable

BException

CError

DRuntimeException

Attempts:

3 left

💡 Hint

Common Mistakes

Extending Exception instead of RuntimeException causes the exception to be checked.

Extending Error is not appropriate for application exceptions.

The custom exception should extend RuntimeException to be an unchecked exception suitable for Spring Boot.

2fill in blank

medium

Complete the code to annotate the exception handler method to catch ResourceNotFoundException.

Spring Boot

@[1](ResourceNotFoundException.class)
public ResponseEntity<String> handleNotFound(ResourceNotFoundException ex) {
    return ResponseEntity.status(HttpStatus.NOT_FOUND).body(ex.getMessage());
}

Drag options to blanks, or click blank then click option'

ARequestMapping

BExceptionHandler

CResponseStatus

DControllerAdvice

Attempts:

3 left

💡 Hint

Common Mistakes

Using @RequestMapping instead of @ExceptionHandler.

Confusing @ControllerAdvice with @ExceptionHandler.

@ExceptionHandler is used to mark a method that handles specific exceptions in Spring Boot.

3fill in blank

hard

Fix the error in the exception handler method to return NOT_FOUND status correctly.

Spring Boot

return ResponseEntity.status([1]).body(ex.getMessage());

Drag options to blanks, or click blank then click option'

AHttpStatus.OK

BHttpStatus.INTERNAL_SERVER_ERROR

CHttpStatus.NOT_FOUND

DHttpStatus.BAD_REQUEST

Attempts:

3 left

💡 Hint

Common Mistakes

Returning HttpStatus.OK (200) which means success.

Using INTERNAL_SERVER_ERROR (500) which is for server errors.

HttpStatus.NOT_FOUND (404) is the correct status code to indicate a resource was not found.

4fill in blank

hard

Fill both blanks to create a global exception handler class with proper annotation and method signature.

Spring Boot

@[1]
public class GlobalExceptionHandler {

    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<String> [2](ResourceNotFoundException ex) {
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(ex.getMessage());
    }
}

Drag options to blanks, or click blank then click option'

AControllerAdvice

BhandleResourceNotFound

CRestController

DhandleException

Attempts:

3 left

💡 Hint

Common Mistakes

Using @RestController instead of @ControllerAdvice for global exception handling.

Using generic method names like handleException without clarity.

@ControllerAdvice marks the class as a global exception handler. The method name can be descriptive like handleResourceNotFound.

5fill in blank

hard

Fill all three blanks to throw the custom exception when a resource is not found in the service method.

Spring Boot

public Resource getResourceById(Long id) {
    return repository.findById(id).orElseThrow(() -> new [1]([2]));
}

// Message constant
private static final String [3] = "Resource not found with id: ";

Drag options to blanks, or click blank then click option'

AResourceNotFoundException

B"Resource not found with id: " + id

CNOT_FOUND_MESSAGE

DIllegalArgumentException

Attempts:

3 left

💡 Hint

Common Mistakes

Throwing IllegalArgumentException instead of the custom exception.

Using a message variable name that is not defined.

The method throws ResourceNotFoundException with a message. The message constant is named NOT_FOUND_MESSAGE.

Practice

1. What is the main purpose of handling not found exceptions in a Spring Boot application?

easy

A. To improve database performance

B. To log all user activities

C. To automatically retry failed requests

D. To return a clear 404 status when a requested resource is missing

Solution

1. Step 1: Understand the role of not found exceptions

   Not found exceptions indicate that a requested resource does not exist on the server.

2. Step 2: Identify the correct response behavior

   Returning a 404 HTTP status code clearly informs the client that the resource is missing.

3. Final Answer:

   To return a clear 404 status when a requested resource is missing -> Option D

4. Quick Check:

   Not found exceptions = 404 status [OK]

Hint: Not found means resource missing, so send 404 status [OK]

Common Mistakes:

• Confusing not found with server errors
• Thinking it improves database speed
• Assuming it retries requests automatically

2. Which annotation is used in Spring Boot to mark a custom exception class to return HTTP 404 status automatically?

easy

A. @ResponseStatus(HttpStatus.NOT_FOUND)

B. @ExceptionHandler(HttpStatus.NOT_FOUND)

C. @NotFoundException

D. @HttpStatusCode(404)

Solution

1. Step 1: Recall Spring Boot annotations for HTTP status

   The @ResponseStatus annotation sets the HTTP status code for exceptions or controller methods.

2. Step 2: Match the annotation to 404 status

   Using @ResponseStatus(HttpStatus.NOT_FOUND) on a custom exception class sends 404 automatically.

3. Final Answer:

   @ResponseStatus(HttpStatus.NOT_FOUND) -> Option A

4. Quick Check:

   @ResponseStatus + NOT_FOUND = 404 [OK]

Hint: Use @ResponseStatus with NOT_FOUND for 404 exceptions [OK]

Common Mistakes:

• Using @ExceptionHandler instead of @ResponseStatus
• Assuming @NotFoundException is a valid annotation
• Using incorrect annotation names

3. Given this controller method in Spring Boot:

 @GetMapping("/items/{id}")
 public Item getItem(@PathVariable Long id) {
     return itemRepository.findById(id)
         .orElseThrow(() -> new ItemNotFoundException(id));
 }

What happens if the item with the given id does not exist?

medium

A. The method returns null and HTTP 200 status

B. An ItemNotFoundException is thrown and HTTP 404 status is returned

C. The server crashes with a NullPointerException

D. The method returns an empty Item object

Solution

1. Step 1: Analyze the use of orElseThrow

   If the item is not found, orElseThrow triggers the custom ItemNotFoundException.

2. Step 2: Understand exception handling with @ResponseStatus

   If ItemNotFoundException is annotated with @ResponseStatus(HttpStatus.NOT_FOUND), Spring returns 404 status.

3. Final Answer:

   An ItemNotFoundException is thrown and HTTP 404 status is returned -> Option B

4. Quick Check:

   orElseThrow + @ResponseStatus = 404 error [OK]

Hint: orElseThrow triggers exception, annotated exception sends 404 [OK]

Common Mistakes:

• Assuming null is returned instead of exception
• Confusing 404 with 500 server error
• Thinking empty object is returned

4. Consider this code snippet:

 @ResponseStatus(HttpStatus.NOT_FOUND)
 public class ProductNotFoundException extends RuntimeException {
     public ProductNotFoundException(Long id) {
         super("Product " + id + " not found");
     }
 }

 @GetMapping("/products/{id}")
 public Product getProduct(@PathVariable Long id) {
     return productRepo.findById(id).orElseThrow(() -> new ProductNotFoundException(id));
 }

What is the likely problem if the client always receives HTTP 500 instead of 404 when a product is missing?

medium

A. The exception is thrown but Spring does not map it to 404

B. The exception is not annotated with @ResponseStatus

C. The controller method does not handle the exception explicitly

D. The exception class is missing a no-argument constructor

Solution

1. Step 1: Verify annotation presence

   The exception class is correctly annotated with @ResponseStatus(HttpStatus.NOT_FOUND).

2. Step 2: Understand Spring's exception mapping

   If Spring returns 500, it means it does not recognize the exception mapping to 404, possibly due to package scanning or configuration issues.

3. Final Answer:

   The exception is thrown but Spring does not map it to 404 -> Option A

4. Quick Check:

   Annotated exception but 500 means mapping failed [OK]

Hint: 500 instead of 404 means Spring missed exception mapping [OK]

Common Mistakes:

• Assuming missing no-arg constructor causes 500
• Thinking @ResponseStatus is missing when it is present
• Believing explicit handler is always required

5. You want to create a global exception handler in Spring Boot that returns a JSON error with 404 status and a message when any ResourceNotFoundException occurs. Which approach correctly achieves this?

hard

A. Use @RestController on the exception class and return 404 status

B. Annotate ResourceNotFoundException with @ResponseStatus(HttpStatus.NOT_FOUND) only, no handler needed

C. Create a class annotated with @ControllerAdvice and a method with @ExceptionHandler(ResourceNotFoundException.class) returning ResponseEntity with status 404 and error body

D. Throw ResponseStatusException with 404 inside every controller method manually

Solution

1. Step 1: Understand global exception handling

   Using @ControllerAdvice with @ExceptionHandler allows centralized handling of exceptions across controllers.

2. Step 2: Return ResponseEntity with 404 and JSON body

   The handler method can build a ResponseEntity with HttpStatus.NOT_FOUND and a JSON error message for clients.

3. Final Answer:

   Create a class annotated with @ControllerAdvice and a method with @ExceptionHandler(ResourceNotFoundException.class) returning ResponseEntity with status 404 and error body -> Option C

4. Quick Check:

   Global handler + ResponseEntity = custom 404 JSON [OK]

Hint: Use @ControllerAdvice + @ExceptionHandler for global JSON 404 [OK]

Common Mistakes:

• Relying only on @ResponseStatus without custom JSON body
• Annotating exception class as controller
• Manually throwing exceptions in every method