How do I get my own Excpetion into the client?

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cmp...@zfin.org

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Nov 20, 2018, 10:14:44 AM11/20/18

to RestyGWT

When I throw my own Exception in my controller class somehow, Restygwt seems to ignore this and return a 200 HTTP status code.

If I set my status code to 500 I get a FailedResponseException in the client I cannot inject an error message.

How can I throw an exception and have the client code pick up that exception with my error message?

Thanks.

Stanislav Spiridonov

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Nov 22, 2018, 2:30:35 AM11/22/18

to RestyGWT

Hi,

There is no simple way to do it. In my applications, I use the HTTP codes for exceptions from backend that should be processed on frontend along with serialized exception in the response body.

1. All such exception inherited from a base class - GwtException

@JsonIgnoreProperties({ "cause", "stackTrace", "localizedMessage", "suppressed" })
public class GwtException extends RuntimeException {

	private static final long serialVersionUID = -2385815955673412683L;

	public enum ErrorCode {
		GWT_EXCEPTION(500),
		ACCESS_DENIDED_REST_EXCEPTION(403),
		ANONYMOUS_USER_REST_EXCEPTION(600),
		//...oters
		EXPIRED_AUTH_TOKEN_EXCEPTION(609),
                ;

		private final int code;

		private ErrorCode(final int code) {
			this.code = code;
		}

		public int getCode() {
			return code;
		}

		public static ErrorCode find(final int code) {
			final ErrorCode[] values = ErrorCode.values();
			for (final ErrorCode value : values) {
				if (value.getCode() == code) {
					return value;
				}
			}
			return GWT_EXCEPTION;
		}

	}

	private int code = 500;
	private String message;

	public GwtException() {
		super();
	}

	public GwtException(final String message) {
		super(message);
		this.message = message;
	}

	public GwtException(final Throwable cause) {
		super(cause);
	}

	public GwtException(final String message, final Throwable cause) {
		super(message, cause);
		this.message = message;
	}

	public int getCode() {
		return code;
	}

	/**
	 * @param code
	 *            the code to set
	 */
	public void setCode(final int code) {
		this.code = code;
	}

	/**
	 * @return the message
	 */
	@Override
	public String getMessage() {
		return message;
	}

	/**
	 * @param message
	 *            the message to set
	 */
	public void setMessage(final String message) {
		this.message = message;
	}

}

2. Methods in controllers simple throws necessary exceptions

3. Base controller registers the following exception handler. So exception cached and result response contains code and serialized exception in the body

	@ExceptionHandler(GwtException.class)
	public ResponseEntity<GwtException> setStatusException(final GwtException ex) {
		return ResponseEntity.status(ex.getCode()).body(ex);
	}

4. On the client side, I register the exception mapper and process know exceptions.

public class AdminModuleEntryPoint extends AbstractModuleEntryPoint {
    //....
	public static interface AnonymousUserRestExceptionMapper extends ObjectMapper<AnonymousUserRestException> {}
	private static final AnonymousUserRestExceptionMapper anonymousUserRestExceptionMapper = GWT.create(AnonymousUserRestExceptionMapper.class);
        //.....

	public void onModuleLoad() {
		// ...
		Defaults.setExceptionMapper(new ExceptionMapper() {
			@Override
			public Throwable createFailedStatusException(final Method method, final Response response) {
				final int statusCode = response.getStatusCode();
				final ErrorCode errorCode = GwtException.ErrorCode.find(statusCode);
				switch (errorCode) {
				case ANONYMOUS_USER_REST_EXCEPTION:
					return anonymousUserRestExceptionMapper.read(response.getText());
				case NO_USER_REST_EXCEPTION:
					return noUserRestExceptionMapper.read(response.getText());
                                //.....
				default:
					return new FailedResponseException(response);
				}
			}
		});
                //......
	}