Spring MVC: return a RFC7807 problem object for Spring controller exception

Problem.java

package fr.da_sha1.exceptions;

//... imports are skipped for simplicity

/**
 * Model class to send error details to a client in a form of a Problem details object, described in RFC7807.
 * Inspired  * by <a href="https://github.com/zalando/problem">zalando/problem</a> library.
 * For more information please refer to https://tools.ietf.org/html/rfc7807
 * @author Daria HERVIEUX
 */
public class Problem {

    private static final URI DEFAULT_URI = URI.create("about:blank");

    private final URI type;
    private final String title;
    private final String detail;
    private final HttpStatus status;
    private final Map<String, Object> customAttributes;

    /**
     * Instantiates a problem object.
     *
     * @param type a unique uri referencing the type of the problem
     * @param title title of the type of the problem
     * @param detail details of the particular instance of the problem
     * @param status Https status code associated
     * @param customAttributes a map of attributes associated with the particular instance of the problem
     */
    private Problem(URI type, String title, String detail, HttpStatus status,
            Map<String, Object> customAttributes) {
        this.type = type == null ? DEFAULT_URI : type;
        this.title = title;
        this.detail = detail;
        this.status = status;
        this.customAttributes = customAttributes;

    }

    /**
     * An absolute URI that identifies the problem type. When dereferenced, it SHOULD provide human-readable
     * documentation for the problem type (e.g., using HTML). When this member is not present, its value is assumed to
     * be "about:blank".
     *
     * @return an absolute URI that identifies this problem's type
     */
    public URI getType() {
        return type;
    }

    /**
     * A short, human-readable summary of the problem type. It SHOULD NOT change from occurrence to occurrence of the
     * problem, except for purposes of localisation.
     *
     * @return a short, human-readable summary of this problem
     */
    public String getTitle() {
        return title;
    }


    /**
     * A human readable explanation specific to this occurrence of the problem.
     *
     * @return A human readable explaination of this problem
     */
    public String getDetail() {
        return detail;
    }

    /**
     * The HTTP status code generated by the origin server for this occurrence of the problem.
     *
     * @return the HTTP status code
     */
    public HttpStatus getStatus() {
        return status;
    }

    /**
     * Optional, additional attributes of the problem.
     *
     * @return additional parameters
     */
    public Map<String, Object> getCustomAttributes() {
        return new LinkedHashMap<>(customAttributes);
    }

    public static final class ProblemBuilder {

        private static final Set<String> RESERVED_PROPERTIES = new HashSet<>(Arrays.asList(
                "type", "title", "status", "detail", "instance", "cause"
        ));
        private final Map<String, Object> parameters = new LinkedHashMap<>();
        private URI type;
        private String title;
        private HttpStatus status;
        private String detail;


        private ProblemBuilder() {
        }

        public static ProblemBuilder newBuilder() {
            return new ProblemBuilder();
        }

        public ProblemBuilder withType(@Nullable final URI type) {
            this.type = type;
            return this;
        }

        public ProblemBuilder withTitle(@Nullable final String title) {
            this.title = title;
            return this;
        }

        public ProblemBuilder withStatus(@Nullable final HttpStatus status) {
            this.status = status;
            return this;
        }

        public ProblemBuilder withDetail(@Nullable final String detail) {
            this.detail = detail;
            return this;
        }

        /**
         * Adds a custom attribute corresponding to an instance of the problem.
         *
         * @param key property name
         * @param value property value
         * @return problem builder current instance for chaining 
         */
        public ProblemBuilder with(final String key, final Object value) {
            if (RESERVED_PROPERTIES.contains(key)) {
                throw new IllegalArgumentException("Property " + key + " is reserved");
            }
            parameters.put(key, value);
            return this;
        }

        public Problem build() {
            return new Problem(type, title, detail, status, new LinkedHashMap<>(parameters));
        }

    }
}

RestResponseExceptionHandler.java

package fr.da_sha1.exceptions;

//... imports are skipped for simplicity

/**
 * Spring MVC exception handler for exception thrown by Spring controllers.
 * @author Daria HERVIEUX
 */
@ControllerAdvice
public class RestResponseExceptionHandler extends ResponseEntityExceptionHandler {

    private static final String PROBLEMS_SCHEME = "https";
    private static final String PROBLEMS_HOST = "errors.da-sha1.fr";
    private static final String BEGINNING_MSG_IMPOSSIBLE_FULFILL_REQUEST = "Impossible to fulfill the request. %s";

    private static final Logger log = LoggerFactory.getLogger(RestResponseExceptionHandler.class);

    // application specific exceptions
  
    @ExceptionHandler(value = {IllegalArgumentException.class, IllegalStateException.class})
    protected ResponseEntity<Object> handleInternalError(RuntimeException ex, WebRequest request) {
        return getObjectResponseEntity(ex, request, HttpStatus.INTERNAL_SERVER_ERROR,
                ProblemType.UNEXPECTED_ERROR,
                ex.getMessage());
    }

    @ExceptionHandler(value = {OperationFailedException.class})
    protected ResponseEntity<Object> handleOperationFailedException(OperationFailedException ex, WebRequest request) {
        return getObjectResponseEntity(ex, request, HttpStatus.INTERNAL_SERVER_ERROR,
                ProblemType.UNEXPECTED_ERROR,
                String.format(BEGINNING_MSG_IMPOSSIBLE_FULFILL_REQUEST, ex.getMessage()));
    }

    //... the full list of exception is skipped for simplicity

  // overriding Spring exception handling  
  @Override
    protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex,
            HttpHeaders headers, HttpStatus status, WebRequest request) {
        return getObjectResponseEntity(ex, request, status, ProblemType.INVALID_INPUT, ex.getMessage());
    }

    @Override
    protected ResponseEntity<Object> handleHttpMessageNotReadable(HttpMessageNotReadableException ex,
            HttpHeaders headers, HttpStatus status, WebRequest request) {
        return getObjectResponseEntity(ex, request, status, ProblemType.INVALID_INPUT, ex.getMessage());
    }

    //... the full list of overrides is skipped for simplicity

    @Override
    @Nullable
    protected ResponseEntity<Object> handleAsyncRequestTimeoutException(AsyncRequestTimeoutException ex,
            HttpHeaders headers, HttpStatus status, WebRequest request) {
        if (super.handleAsyncRequestTimeoutException(ex, headers, status, request) != null) {
            return getObjectResponseEntity(ex, request, status, ProblemType.UNEXPECTED_ERROR, ex.getMessage());
        }
        return null;
    }

    private ResponseEntity<Object> getObjectResponseEntity(Exception ex, WebRequest request,
            HttpStatus code,
            ProblemType type,
            String problemDetails) {
        log.error("Exception message : {} - HttpStatus code = {}", problemDetails, code, ex);
        String details = (problemDetails == null) ? "" : (": " + problemDetails);
        URI uri = null;
        try {
            uri = new URI(PROBLEMS_SCHEME, PROBLEMS_HOST, "/" + type.getUriPath(), null);
        } catch (URISyntaxException e) {
            log.warn("Impossible to create a problem type URI for the code='{}' and the problem='{}'", code, type,e);
        }
        // creating RFC7807 compliant problem object
        Problem bodyOfResponse = Problem.ProblemBuilder
                .newBuilder()
                .withType(uri)
                .withTitle(type.getTitle())
                .withDetail(details)
                .withStatus(code)
                .build();
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_PROBLEM_JSON_UTF8);
        
        // using super-class method
        return handleExceptionInternal(ex, bodyOfResponse,
                headers, code, request);
    }
}