@ExceptionHandler in controllers in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to handle exceptions in a Spring Boot controller method.

Spring Boot

public class MyController {
    @[1]
    public ResponseEntity<String> handleException(Exception ex) {
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("Error occurred");
    }
}

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

ARequestMapping

BPostMapping

CGetMapping

DExceptionHandler

Attempts:

3 left

💡 Hint

Common Mistakes

Using @GetMapping or @PostMapping instead of @ExceptionHandler

Forgetting to annotate the method

The @ExceptionHandler annotation is used to define a method that handles exceptions thrown by controller methods.

2fill in blank

medium

Complete the code to specify which exception type the handler method should catch.

Spring Boot

@ExceptionHandler([1].class)
public ResponseEntity<String> handleNotFound(Exception ex) {
    return ResponseEntity.status(HttpStatus.NOT_FOUND).body("Resource not found");
}

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

AResourceNotFoundException

BRuntimeException

CNullPointerException

DIOException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a general exception like RuntimeException instead of a specific one

Not specifying the exception class

You specify the exception class inside @ExceptionHandler to catch that specific exception type.

3fill in blank

hard

Fix the error in the exception handler method signature to correctly handle exceptions.

Spring Boot

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

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

AString

BException

CResourceNotFoundException

DHttpServletRequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic Exception type when a specific exception is declared

Using unrelated types like String or HttpServletRequest

The method parameter should be the same exception type declared in @ExceptionHandler to access its specific methods.

4fill in blank

hard

Fill both blanks to create a global exception handler class with proper annotations.

Spring Boot

@[1]
public class GlobalExceptionHandler {
    @[2]
    public ResponseEntity<String> handleAllExceptions(Exception ex) {
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("Server error");
    }
}

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

AControllerAdvice

BRestController

CExceptionHandler

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using @RestController instead of @ControllerAdvice for global handling

Missing @ExceptionHandler on the method

@ControllerAdvice marks the class as a global exception handler, and @ExceptionHandler marks the method to handle exceptions.

5fill in blank

hard

Fill all three blanks to handle a specific exception and return a custom message with status.

Spring Boot

@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

Mismatching exception class and parameter type

Using wrong HTTP status codes

The method handles CustomException and returns a 400 Bad Request status with a custom message.

Practice

1. What is the main purpose of using @ExceptionHandler in a Spring Boot controller?

easy

A. To catch and handle exceptions thrown in controller methods

B. To define the URL path for a controller method

C. To inject dependencies into the controller

D. To configure database connections

Solution

1. Step 1: Understand the role of @ExceptionHandler

   @ExceptionHandler is used to catch exceptions that occur in controller methods to prevent the app from crashing.

2. Step 2: Identify what @ExceptionHandler does in controllers

   It allows sending user-friendly error messages and proper HTTP status codes when exceptions happen.

3. Final Answer:

   To catch and handle exceptions thrown in controller methods -> Option A

4. Quick Check:

   @ExceptionHandler catches exceptions [OK]

Hint: Remember: @ExceptionHandler handles errors in controllers [OK]

Common Mistakes:

• Confusing @ExceptionHandler with URL mapping annotations
• Thinking it injects dependencies
• Assuming it configures database settings

2. Which of the following is the correct way to declare an exception handler method in a Spring Boot controller?

easy

A. @RequestMapping(Exception.class) public String handleError() { return "error"; }

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

C. @Autowired(Exception.class) public String handleError() { return "error"; }

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

Solution

1. Step 1: Identify the correct annotation for exception handling

   @ExceptionHandler is the annotation used to mark methods that handle exceptions.

2. Step 2: Check the method signature

   The method should be annotated with @ExceptionHandler(Exception.class) and return a response, here a String view name.

3. Final Answer:

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

4. Quick Check:

   @ExceptionHandler syntax [OK]

Hint: Use @ExceptionHandler with exception class to handle errors [OK]

Common Mistakes:

• Using @RequestMapping or @GetMapping instead of @ExceptionHandler
• Misusing @Autowired annotation
• Missing the exception class in @ExceptionHandler

3. Given the following controller code snippet, what will be the HTTP status code returned when a NullPointerException occurs?

@RestController
public class MyController {
  @GetMapping("/test")
  public String test() {
    throw new NullPointerException("Null error");
  }

  @ExceptionHandler(NullPointerException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  public String handleNullPointer() {
    return "Null pointer error handled";
  }
}

medium

A. 200 OK

B. 400 Bad Request

C. 500 Internal Server Error

D. 404 Not Found

Solution

1. Step 1: Identify the exception and handler

   The controller throws NullPointerException, which is caught by the method annotated with @ExceptionHandler(NullPointerException.class).

2. Step 2: Check the response status annotation

   The handler method has @ResponseStatus(HttpStatus.BAD_REQUEST), so it sets the HTTP status to 400.

3. Final Answer:

   400 Bad Request -> Option B

4. Quick Check:

   @ResponseStatus sets HTTP code = 400 [OK]

Hint: Look for @ResponseStatus on @ExceptionHandler method [OK]

Common Mistakes:

• Assuming default 500 error without @ResponseStatus
• Confusing exception type with HTTP status
• Ignoring the @ExceptionHandler method

4. Consider this controller code snippet:

@RestController
public class DemoController {
  @GetMapping("/demo")
  public String demo() {
    throw new IllegalArgumentException("Invalid argument");
  }

  @ExceptionHandler(NullPointerException.class)
  public String handleNull() {
    return "Null error";
  }
}

What will happen when the /demo endpoint is called?

medium

A. The exception will be handled by handleNull method

B. The response will be "Null error" with HTTP 200

C. The exception will not be handled and a 500 error is returned

D. The server will return HTTP 404 Not Found

Solution

1. Step 1: Identify the thrown exception

   The method throws IllegalArgumentException, but the handler only catches NullPointerException.

2. Step 2: Check if exception is handled

   Since no handler matches IllegalArgumentException, Spring Boot returns a default 500 Internal Server Error.

3. Final Answer:

   The exception will not be handled and a 500 error is returned -> Option C

4. Quick Check:

   Handler mismatch causes 500 error [OK]

Hint: Handler must match exception type exactly [OK]

Common Mistakes:

• Assuming handler catches all exceptions
• Thinking handler method runs for different exception types
• Expecting 404 instead of 500 error

5. You want to create a global exception handler in Spring Boot that catches RuntimeException for all controllers and returns a JSON error message with HTTP status 500. Which approach correctly achieves this?

hard

A. Create a class annotated with @ControllerAdvice and define a method with @ExceptionHandler(RuntimeException.class) returning a JSON response and @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR).

B. Add @ExceptionHandler(RuntimeException.class) method inside each controller class returning a view name.

C. Use @RestController on a class with @ExceptionHandler(Exception.class) returning a String message.

D. Configure exception handling in application.properties file.

Solution

1. Step 1: Understand global exception handling

   @ControllerAdvice allows defining exception handlers that apply to all controllers globally.

2. Step 2: Define handler method for RuntimeException

   Use @ExceptionHandler(RuntimeException.class) with @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR) to set status 500 and return JSON response.

3. Final Answer:

   Create a class annotated with @ControllerAdvice and define a method with @ExceptionHandler(RuntimeException.class) returning a JSON response and @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR). -> Option A

4. Quick Check:

   Global handler uses @ControllerAdvice + @ExceptionHandler [OK]

Hint: Use @ControllerAdvice for global exception handling [OK]

Common Mistakes:

• Putting handlers only inside controllers for global effect
• Using application.properties for exception handling
• Not setting proper HTTP status in handler