ResponseEntityExceptionHandler in Spring Boot

Introduction

ResponseEntityExceptionHandler helps you handle errors in your Spring Boot app in one place. It makes your app send clear error messages to users.

You want to send custom error messages when something goes wrong in your app.

You want to handle common errors like 'not found' or 'bad request' without repeating code.

You want to keep your code clean by managing exceptions in one class.

You want to return HTTP status codes with error details to the client.

You want to log errors and send friendly messages instead of default server errors.

Syntax

Spring Boot

public class MyExceptionHandler extends ResponseEntityExceptionHandler {

    @Override
    protected ResponseEntity<Object> handleMethodArgumentNotValid(
            MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
        // custom error response
        return new ResponseEntity<>("Custom error message", HttpStatus.BAD_REQUEST);
    }

    @ExceptionHandler(MyCustomException.class)
    public ResponseEntity<Object> handleMyCustomException(MyCustomException ex) {
        return new ResponseEntity<>(ex.getMessage(), HttpStatus.BAD_REQUEST);
    }
}

Extend ResponseEntityExceptionHandler to override default error handling methods.

Use @ExceptionHandler to handle specific exceptions not covered by default methods.

Examples

This example customizes the response when the JSON in a request is invalid.

Spring Boot

public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {

    @Override
    protected ResponseEntity<Object> handleHttpMessageNotReadable(
            HttpMessageNotReadableException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
        return new ResponseEntity<>("Malformed JSON request", HttpStatus.BAD_REQUEST);
    }
}

This method handles a custom exception and returns a 404 status with a message.

Spring Boot

@ExceptionHandler(ResourceNotFoundException.class)
public ResponseEntity<Object> handleResourceNotFound(ResourceNotFoundException ex) {
    return new ResponseEntity<>("Resource not found", HttpStatus.NOT_FOUND);
}

Sample Program

This class catches validation errors and illegal argument exceptions. It sends clear messages and HTTP 400 status to the client.

Spring Boot

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.context.request.WebRequest;
import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;

@ControllerAdvice
public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {

    @Override
    protected ResponseEntity<Object> handleMethodArgumentNotValid(
            MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
        String errorMessage = "Validation failed: " + ex.getBindingResult().getErrorCount() + " error(s)";
        return new ResponseEntity<>(errorMessage, HttpStatus.BAD_REQUEST);
    }

    @ExceptionHandler(IllegalArgumentException.class)
    public ResponseEntity<Object> handleIllegalArgument(IllegalArgumentException ex) {
        return new ResponseEntity<>("Illegal argument: " + ex.getMessage(), HttpStatus.BAD_REQUEST);
    }
}

Important Notes

Use @ControllerAdvice to apply exception handling globally across controllers.

Override methods from ResponseEntityExceptionHandler to customize common Spring exceptions.

Always return meaningful messages and proper HTTP status codes for better client understanding.

Summary

ResponseEntityExceptionHandler centralizes error handling in Spring Boot apps.

Override its methods or use @ExceptionHandler for custom error responses.

This improves user experience by sending clear, consistent error messages.

Practice

1. What is the main purpose of ResponseEntityExceptionHandler in a Spring Boot application?

easy

A. To handle user authentication and authorization

B. To centralize and customize error handling for REST controllers

C. To manage database connections automatically

D. To configure application properties at runtime

Solution

1. Step 1: Understand the role of ResponseEntityExceptionHandler

   This class provides a centralized way to handle exceptions thrown by REST controllers in Spring Boot.

2. Step 2: Compare with other options

   Options A, B, and D relate to authentication, database management, and configuration, which are not the responsibility of ResponseEntityExceptionHandler.

3. Final Answer:

   To centralize and customize error handling for REST controllers -> Option B

4. Quick Check:

   ResponseEntityExceptionHandler centralizes REST error handling [OK]

Hint: Remember: ResponseEntityExceptionHandler handles REST errors centrally [OK]

Common Mistakes:

• Confusing it with security or database management
• Thinking it configures app properties
• Assuming it handles UI rendering errors

2. Which method signature correctly overrides a method from ResponseEntityExceptionHandler to handle MethodArgumentNotValidException?

easy

A. protected ResponseEntity<Object> handleValidationException(Exception ex, HttpHeaders headers, HttpStatus status, WebRequest request)

B. public void handleMethodArgumentNotValid(Exception ex)

C. private ResponseEntity<String> handleValidationError(MethodArgumentNotValidException ex)

D. protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request)

Solution

1. Step 1: Check method signature requirements

   ResponseEntityExceptionHandler requires protected method returning ResponseEntity<Object> with parameters (MethodArgumentNotValidException, HttpHeaders, HttpStatus, WebRequest).

2. Step 2: Match options to signature

   protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) matches exactly. Options B and C have wrong access modifiers or parameters. protected ResponseEntity<Object> handleValidationException(Exception ex, HttpHeaders headers, HttpStatus status, WebRequest request) uses wrong exception type and method name.

3. Final Answer:

   protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) -> Option D

4. Quick Check:

   Exact override signature required [OK]

Hint: Override with exact signature including all parameters [OK]

Common Mistakes:

• Using wrong access modifier like public or private
• Missing parameters like HttpHeaders or WebRequest
• Changing return type to something other than ResponseEntity<Object>

3. Given this code snippet inside a class extending ResponseEntityExceptionHandler:

  @Override
  protected ResponseEntity<Object> handleHttpMessageNotReadable(HttpMessageNotReadableException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
      String body = "Malformed JSON request";
      return new ResponseEntity<>(body, headers, HttpStatus.BAD_REQUEST);
  }

What will be the HTTP status code returned when a malformed JSON is sent to the API?

medium

A. 200 OK

B. 500 Internal Server Error

C. 400 Bad Request

D. 404 Not Found

Solution

1. Step 1: Analyze the overridden method

   The method returns a ResponseEntity with status HttpStatus.BAD_REQUEST when JSON is malformed.

2. Step 2: Identify the HTTP status code for BAD_REQUEST

   BAD_REQUEST corresponds to HTTP status code 400.

3. Final Answer:

   400 Bad Request -> Option C

4. Quick Check:

   BAD_REQUEST = 400 [OK]

Hint: BAD_REQUEST means 400 status code [OK]

Common Mistakes:

• Confusing BAD_REQUEST with 500 Internal Server Error
• Assuming 200 OK is returned on error
• Mixing up 404 Not Found with validation errors

4. Consider this custom exception handler class:

  @ControllerAdvice
  public class CustomExceptionHandler extends ResponseEntityExceptionHandler {

      @ExceptionHandler(NullPointerException.class)
      public ResponseEntity<Object> handleNullPointer(NullPointerException ex, WebRequest request) {
          String body = "Null value found";
          return new ResponseEntity<>(body, HttpStatus.INTERNAL_SERVER_ERROR);
      }

      @Override
      protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
          String body = "Validation failed";
          return new ResponseEntity<>(body, HttpStatus.BAD_REQUEST);
      }
  }

If a NullPointerException occurs, what will be the HTTP status code returned?

medium

A. 500 Internal Server Error

B. 400 Bad Request

C. 404 Not Found

D. 200 OK

Solution

1. Step 1: Identify the handler for NullPointerException

   The method annotated with @ExceptionHandler(NullPointerException.class) returns status INTERNAL_SERVER_ERROR.

2. Step 2: Map INTERNAL_SERVER_ERROR to HTTP status code

   INTERNAL_SERVER_ERROR corresponds to HTTP status 500.

3. Final Answer:

   500 Internal Server Error -> Option A

4. Quick Check:

   NullPointerException handled with 500 status [OK]

Hint: Check @ExceptionHandler annotation for exception type [OK]

Common Mistakes:

• Assuming validation error handler is called for NullPointerException
• Confusing 400 Bad Request with 500 Internal Server Error
• Ignoring @ExceptionHandler methods

5. You want to customize error responses for both validation errors and JSON parse errors in your Spring Boot REST API. Which approach correctly combines ResponseEntityExceptionHandler methods and @ExceptionHandler to achieve this?

hard

A. Override handleMethodArgumentNotValid for validation errors and add an @ExceptionHandler for HttpMessageNotReadableException

B. Use only @ExceptionHandler methods for all exceptions, no overrides needed

C. Override handleHttpMessageNotReadable for validation errors and use @ExceptionHandler for MethodArgumentNotValidException

D. Override handleExceptionInternal to catch all exceptions globally

Solution

1. Step 1: Understand which methods handle which exceptions

   handleMethodArgumentNotValid handles validation errors; handleHttpMessageNotReadable handles JSON parse errors.

2. Step 2: Combine overrides and @ExceptionHandler correctly

   Override handleMethodArgumentNotValid for validation errors and use @ExceptionHandler for HttpMessageNotReadableException to customize JSON parse error responses.

3. Final Answer:

   Override handleMethodArgumentNotValid for validation errors and add an @ExceptionHandler for HttpMessageNotReadableException -> Option A

4. Quick Check:

   Use overrides for validation, @ExceptionHandler for JSON errors [OK]

Hint: Override validation method, @ExceptionHandler for JSON parse errors [OK]

Common Mistakes:

• Mixing exception types in wrong handlers
• Using only @ExceptionHandler without overrides
• Overriding wrong methods for given exceptions