@ControllerAdvice for global handling in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a global exception handler class using @ControllerAdvice.

Spring Boot

import org.springframework.web.bind.annotation.[1];

@[1]
public class GlobalExceptionHandler {

}

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

AControllerAdvice

BRestController

CService

DComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using @RestController instead of @ControllerAdvice

Forgetting to import the annotation

Annotating with @Service or @Component which are not for exception handling

The @ControllerAdvice annotation marks a class as a global exception handler in Spring Boot.

2fill in blank

medium

Complete the method annotation to handle exceptions of type NullPointerException globally.

Spring Boot

import org.springframework.web.bind.annotation.ExceptionHandler;

@ExceptionHandler([1].class)
public String handleNullPointer() {
    return "error-null";
}

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

AIOException

BIllegalArgumentException

CRuntimeException

DNullPointerException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different exception type than intended

Omitting the .class suffix

Not annotating the method at all

The @ExceptionHandler annotation specifies which exception type the method handles. Here, it handles NullPointerException.

3fill in blank

hard

Fix the error in the method signature to correctly handle exceptions globally.

Spring Boot

import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.http.HttpStatus;

@ExceptionHandler(Exception.class)
@ResponseStatus([1])
public String handleAllExceptions(Exception ex) {
    return "error";
}

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

AHttpStatus.INTERNAL_SERVER_ERROR

BHttpStatus.NOT_FOUND

CHttpStatus.OK

DHttpStatus.BAD_REQUEST

Attempts:

3 left

💡 Hint

Common Mistakes

Using HTTP 200 OK for error responses

Using HTTP 404 Not Found for exceptions

Not specifying any response status

Using @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR) tells Spring to return HTTP 500 for unhandled exceptions.

4fill in blank

hard

Fill both blanks to create a method that handles IllegalArgumentException and returns a custom error message.

Spring Boot

import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;

@ExceptionHandler([1].class)
@ResponseBody
public String handleIllegalArgument([2] ex) {
    return "Invalid argument: " + ex.getMessage();
}

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

AIllegalArgumentException

BNullPointerException

DException

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching exception types between annotation and parameter

Forgetting to annotate with @ResponseBody for response content

Using a generic Exception type instead of specific

The method handles IllegalArgumentException and takes it as a parameter to access the message.

5fill in blank

hard

Fill all three blanks to create a global handler that returns a ResponseEntity with status and body.

Spring Boot

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.http.HttpStatus;

@ExceptionHandler([1].class)
public ResponseEntity<String> handleCustomException([2] ex) {
    return ResponseEntity.status([3]).body("Custom error: " + ex.getMessage());
}

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

ACustomException

CHttpStatus.BAD_REQUEST

DHttpStatus.NOT_FOUND

Attempts:

3 left

💡 Hint

Common Mistakes

Using different exception types in annotation and parameter

Returning plain String instead of ResponseEntity

Using wrong HTTP status codes

This method handles CustomException and returns a ResponseEntity with HTTP 400 Bad Request status and a custom message.

Practice

1. What is the main purpose of using @ControllerAdvice in a Spring Boot application?

easy

A. To handle exceptions globally for all controllers in one place

B. To define REST endpoints for the application

C. To configure database connections

D. To create scheduled tasks

Solution

1. Step 1: Understand the role of @ControllerAdvice

   @ControllerAdvice is a special annotation in Spring Boot that allows you to write code to handle exceptions or apply logic across all controllers globally.

2. Step 2: Identify its main use

   Its main use is to centralize exception handling so you don't have to repeat error handling code in every controller.

3. Final Answer:

   To handle exceptions globally for all controllers in one place -> Option A

4. Quick Check:

   @ControllerAdvice = global exception handling [OK]

Hint: Think global error handling for all controllers [OK]

Common Mistakes:

• Confusing @ControllerAdvice with @RestController
• Thinking it configures database or tasks
• Assuming it defines endpoints

2. Which of the following is the correct way to declare a global exception handler method inside a @ControllerAdvice class?

easy

A. @Service public String handleError() { return "error"; }

B. @ExceptionHandler(Exception.class) public String handleError() { return "error"; }

C. @GetMapping public String handleError() { return "error"; }

D. @RequestMapping("/error") public String handleError() { return "error"; }

Solution

1. Step 1: Identify the annotation for exception handling

   The correct annotation to handle exceptions globally is @ExceptionHandler with the exception class specified.

2. Step 2: Check method signature and annotation usage

   @ExceptionHandler(Exception.class) public String handleError() { return "error"; } uses @ExceptionHandler(Exception.class) which is correct inside a @ControllerAdvice class to catch all exceptions.

3. Final Answer:

   @ExceptionHandler(Exception.class) public String handleError() { return "error"; } -> Option B

4. Quick Check:

   @ExceptionHandler = global exception method [OK]

Hint: Use @ExceptionHandler with exception class inside @ControllerAdvice [OK]

Common Mistakes:

• Using @RequestMapping or @GetMapping instead of @ExceptionHandler
• Missing exception class in @ExceptionHandler
• Using @Service annotation incorrectly

3. Given the following code snippet, what will be the HTTP response status when a NullPointerException is thrown in any controller?

@ControllerAdvice
public class GlobalExceptionHandler {
  @ExceptionHandler(NullPointerException.class)
  public ResponseEntity<String> handleNullPointer() {
    return new ResponseEntity<>("Null pointer error", HttpStatus.BAD_REQUEST);
  }
}

medium

A. 400 Bad Request with message "Null pointer error"

B. 500 Internal Server Error with default message

C. 200 OK with message "Null pointer error"

D. 404 Not Found with message "Null pointer error"

Solution

1. Step 1: Analyze the @ExceptionHandler method

   The method handles NullPointerException and returns a ResponseEntity with message "Null pointer error" and status BAD_REQUEST.

2. Step 2: Understand HTTP status returned

   HttpStatus.BAD_REQUEST corresponds to 400 status code, so the response will have status 400 with the given message.

3. Final Answer:

   400 Bad Request with message "Null pointer error" -> Option A

4. Quick Check:

   @ExceptionHandler returns 400 status [OK]

Hint: Check ResponseEntity status in @ExceptionHandler method [OK]

Common Mistakes:

• Assuming default 500 error instead of specified status
• Confusing 400 with 200 OK
• Ignoring the returned ResponseEntity status

4. Consider this @ControllerAdvice class:

@ControllerAdvice
public class GlobalHandler {
  @ExceptionHandler(IllegalArgumentException.class)
  public String handleIllegalArgument() {
    return "illegal";
  }

  @ExceptionHandler(Exception.class)
  public String handleAll() {
    return "error";
  }
}

What is the problem if a NullPointerException occurs in a controller?

medium

A. NullPointerException is not handled and causes server error

B. handleIllegalArgument() method will handle NullPointerException incorrectly

C. handleAll() method will handle NullPointerException correctly

D. Compilation error due to multiple @ExceptionHandler methods

Solution

1. Step 1: Identify exception handlers and their scopes

   handleIllegalArgument() handles IllegalArgumentException only; handleAll() handles all Exceptions as a fallback.

2. Step 2: Determine which method handles NullPointerException

   Since NullPointerException is not IllegalArgumentException, handleAll() will catch it as it handles Exception class.

3. Final Answer:

   handleAll() method will handle NullPointerException correctly -> Option C

4. Quick Check:

   More specific handlers first, then general Exception handler [OK]

Hint: General @ExceptionHandler(Exception.class) catches all others [OK]

Common Mistakes:

• Thinking NullPointerException is unhandled
• Assuming multiple handlers cause compile error
• Confusing which handler matches which exception

5. You want to create a global error handler that returns JSON with error details for all exceptions except ResourceNotFoundException, which should return 404 status with a custom message. How should you implement this using @ControllerAdvice?

hard

A. Use a single @ExceptionHandler(Exception.class) method and check exception type inside to return different responses

B. Use @ControllerAdvice only for ResourceNotFoundException and ignore other exceptions

C. Handle ResourceNotFoundException in each controller separately, and use @ControllerAdvice only for other exceptions

D. Create two @ExceptionHandler methods: one for ResourceNotFoundException returning 404 JSON, another for Exception returning generic JSON with 500 status

Solution

1. Step 1: Understand requirement for specific and general handling

   You need one handler for ResourceNotFoundException with 404 and custom JSON, and another for all other exceptions with generic 500 JSON.

2. Step 2: Implement two separate @ExceptionHandler methods in @ControllerAdvice

   One method annotated with @ExceptionHandler(ResourceNotFoundException.class) returns 404 JSON; another with @ExceptionHandler(Exception.class) returns 500 JSON.

3. Final Answer:

   Create two @ExceptionHandler methods: one for ResourceNotFoundException returning 404 JSON, another for Exception returning generic JSON with 500 status -> Option D

4. Quick Check:

   Separate handlers for specific and general exceptions [OK]

Hint: Use multiple @ExceptionHandler methods for different exceptions [OK]

Common Mistakes:

• Using one method with manual type checks inside
• Handling specific exceptions in controllers, not globally
• Ignoring general exceptions in @ControllerAdvice