# GlobalExceptionHandler.java

    package io.github.js0ny.ilp_coursework.exception;

    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.http.HttpStatus;
    import org.springframework.http.converter.HttpMessageNotReadableException;
    import org.springframework.web.bind.annotation.ExceptionHandler;
    import org.springframework.web.bind.annotation.ResponseStatus;
    import org.springframework.web.bind.annotation.RestControllerAdvice;

    import java.util.Map;
    import java.util.Optional;

    /** Class that handles exception or failed request. Map all error requests to 400. */
    @RestControllerAdvice
    public class GlobalExceptionHandler {

        /// Use a logger to save logs instead of passing them to user
        private static final Logger log = LoggerFactory.getLogger(GlobalExceptionHandler.class);
        private final Map<String, String> badRequestMap =
                Map.of("status", "400", "error", "Bad Request");

        @ExceptionHandler(HttpMessageNotReadableException.class)
        @ResponseStatus(HttpStatus.BAD_REQUEST)
        public Map<String, String> handleHttpMessageNotReadable(HttpMessageNotReadableException ex) {
            log.warn("Malformed JSON received: {}", ex.getMessage());
            return badRequestMap;
        }

        @ExceptionHandler(IllegalArgumentException.class)
        @ResponseStatus(HttpStatus.BAD_REQUEST)
        public Map<String, String> handleIllegalArgument(IllegalArgumentException ex) {
            String errorMessage =
                    Optional.ofNullable(ex.getMessage()).orElse("Invalid argument provided.");
            log.warn("Illegal argument in request: {}", errorMessage);
            return badRequestMap;
        }

        @ExceptionHandler(NullPointerException.class)
        @ResponseStatus(HttpStatus.BAD_REQUEST)
        public Map<String, String> handleNullPointerException(Exception ex) {
            log.error("NullPointerException occurred. Return 400 by default.", ex);
            return badRequestMap;
        }

        @ExceptionHandler(Exception.class)
        @ResponseStatus(HttpStatus.BAD_REQUEST)
        public Map<String, String> handleGeneralException(Exception ex) {
            log.error("Fallback exception received: {}", ex.getMessage());
            return badRequestMap;
        }
    }