refactor(engine-rest): Ensure Proper Exception Code Assignment in ExceptionHandlerHelper

[yhao3]

Background

While implementing custom exception handling for my Camunda REST API, I used the ExceptionHandlerHelper class from the engine-rest module to ensure that the behavior of error handling is consistent with the built-in Camunda REST API error handling. The custom exception handler code is as follows:

@ControllerAdvice
public class CustomExceptionHandler extends ResponseEntityExceptionHandler {

    protected static final ExceptionLogger LOGGER = ExceptionLogger.REST_LOGGER;
    private static final ExceptionHandlerHelper DELEGATE = ExceptionHandlerHelper.getInstance();

    @ExceptionHandler
    public ResponseEntity<Object> handleAnyException(Throwable ex, NativeWebRequest request) {
         ExceptionDto exceptionDto = DELEGATE.fromException(ex);
         return handleExceptionInternal((Exception) ex, exceptionDto, buildHeaders(ex), HttpStatusCode.valueOf(DELEGATE.getStatus(ex).getStatusCode()), request);
    }

    @Nullable
    @Override
    protected ResponseEntity<Object> handleExceptionInternal(
            Exception ex,
            @Nullable Object body,
            HttpHeaders headers,
            HttpStatusCode statusCode,
            WebRequest request
    ) {
        LOGGER.log(ex);
        if (body == null) {
            return super.handleExceptionInternal(ex, DELEGATE.fromException(ex), headers, statusCode, request);
        }
        return super.handleExceptionInternal(ex, body, headers, statusCode, request);
    }

    private HttpHeaders buildHeaders(Throwable err) {
        // ...
    }

}

However, the code field value in the response body (ExceptionDto) was always null, resulting in outputs like the following:

{
    "type": "AuthorizationException",
    "message": "The user with id 'tom' does not have 'CREATE' permission on resource 'Deployment'.",
    "code": null,
    "userId": "tom",
    "resourceName": "Deployment",
    "resourceId": null,
    "permissionName": "CREATE",
    "missingAuthorizations": [
        {
            "permissionName": "CREATE",
            "resourceName": "Deployment",
            "resourceId": null
        }
    ]
}

Changes Overview

This PR resolves an issue where the code field in ExceptionDto was always null. The following adjustments were made:

1. Refactored fromException Method: Ensured the provideExceptionCode method is called for all exception types, correctly assigning the exception code.
2. Removed Redundant Code: Eliminated the redundant provideExceptionCode call in the getResponse method to avoid unnecessary processing.

[yanavasileva]

@yhao3, thank you for reaching out to us with this.

We will have look at it in the next weeks.