@ControllerAdvice for global handling in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when an exception is thrown in a controller with @ControllerAdvice?

Consider a Spring Boot application with a @ControllerAdvice class that handles NullPointerException globally. What will happen if a controller method throws a NullPointerException?

Spring Boot

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

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(NullPointerException.class)
    public ResponseEntity<String> handleNullPointer(Exception ex) {
        return ResponseEntity.status(400).body("Null pointer error caught globally");
    }
}

// In some controller:
// public String someMethod() {
//     throw new NullPointerException();
// }

A The global handler method handleNullPointer will catch the exception and return a 400 response with the message.

B The exception will propagate and cause a server error 500 without using the global handler.

C The application will crash because @ControllerAdvice cannot handle NullPointerException.

D The exception will be ignored and the controller will return a successful empty response.

💡 Hint

Think about how @ControllerAdvice works for exceptions thrown in controllers.

@ControllerAdvice with @ExceptionHandler methods catches exceptions thrown in any controller globally. Here, NullPointerException is caught and a custom response is returned.

📝 Syntax

intermediate

Which @ExceptionHandler method signature is correct inside @ControllerAdvice?

You want to handle IllegalArgumentException globally. Which method signature is valid inside a @ControllerAdvice class?

A public ResponseEntity<String> handleIllegalArg(IllegalArgumentException ex)

B public void handleIllegalArg() throws IllegalArgumentException

C public String handleIllegalArg(Exception ex, HttpServletRequest req)

D public int handleIllegalArg(IllegalArgumentException ex)

💡 Hint

The method should accept the exception type and return a response type.

The method must accept the exception type to handle and return a response (like ResponseEntity or String). Option A matches this pattern.

🔧 Debug

advanced

Why is the global exception handler not catching exceptions?

Given this @ControllerAdvice class, exceptions thrown in controllers are not caught. What is the likely cause? @ControllerAdvice public class GlobalHandler { @ExceptionHandler(RuntimeException.class) public String handleRuntime(RuntimeException ex) { return "Error caught"; } } Controllers throw IllegalArgumentException which extends RuntimeException.

A The @ExceptionHandler method must handle IllegalArgumentException explicitly, not RuntimeException.

B The exception is not caught because IllegalArgumentException is not a RuntimeException.

C The @ControllerAdvice class must be annotated with @Component to be detected.

D The @ControllerAdvice class is missing @RestControllerAdvice annotation to handle REST responses.

💡 Hint

Consider the difference between @ControllerAdvice and @RestControllerAdvice for response bodies.

@ControllerAdvice alone does not serialize return values as JSON or response bodies. Using @RestControllerAdvice ensures the response is sent as JSON or text. Without it, the handler may not work as expected for REST APIs.

🧠 Conceptual

advanced

What is the scope of @ControllerAdvice in a Spring Boot app?

Which statement best describes the scope of a class annotated with @ControllerAdvice?

A @ControllerAdvice applies only to controllers in the same package as the advice class.

B @ControllerAdvice applies globally to all controllers in the application by default.

C @ControllerAdvice applies only to controllers explicitly listed in its annotations.

D @ControllerAdvice applies only to controllers annotated with @RestController.

💡 Hint

Think about the default behavior of @ControllerAdvice without filters.

By default, @ControllerAdvice applies globally to all controllers in the Spring Boot application unless filters like basePackages or assignableTypes are specified.

❓ state_output

expert

What is the HTTP status code returned by this global handler?

Given this @ControllerAdvice handler: @ControllerAdvice public class GlobalErrorHandler { @ExceptionHandler(IllegalStateException.class) public ResponseEntity handleIllegalState(IllegalStateException ex) { return ResponseEntity.status(409).body("Conflict error"); } } If a controller throws IllegalStateException, what HTTP status code will the client receive?

A 400

B 500

C 409

D 200

💡 Hint

Look at the ResponseEntity.status() call in the handler.

The handler sets the HTTP status to 409 Conflict explicitly, so the client receives status 409.