public Entity getEntityWithOptions(@PathParam("id") String id, @QueryParam("option") String optValue) {
    if (optValue != null) {
        // Option is an enum
        try {
            Option option = Option.valueOf(optValue);
        } catch (IllegalArgumentException e) {
            throw new BadRequestException(e.getMessage());
        }
        return new Entity(option);
    }
    return new Entity();
}

public class CustomException extends RuntimeException {
    public CustomException(Throwable throwable) {
        super(throwable);
    }

    public CustomException(String string, Throwable throwable) {
        super(string, throwable);
    }

    public CustomException(String string) {
        super(string);
    }

    public CustomException() {
        super();
    }
}

@Provider
public class CustomExceptionMapper implements ExceptionMapper<CustomException> {
    private static Logger logger = Logger.getLogger(CustomExceptionMapper.class.getName());
    /**
     * This constructor is invoked when exception is thrown, after
     * resource-method has been invoked. Using @provider.
     */
    public CustomExceptionMapper() {
        super();
    }

    /**
     * When exception is thrown by the jersey container.This method is invoked
     */
    public Response toResponse(CustomException ex) {
        logger.log(Level.SEVERE, ex.getMessage(), ex);
        Response.ResponseBuilder resp = Response.status(Response.Status.BAD_REQUEST)
                        .entity(ex.getMessage());

        return resp.build();
    }
}

public Entity getEntityWithOptions(@PathParam("id") String id,
                                   @QueryParam("option") String optValue)
                                   throws CustomException {
    if (optValue != null) {
        // Option is an enum
        try {
            Option option = Option.valueOf(optValue);
        } catch (IllegalArgumentException e) {
            throw new CustomException(e.getMessage(),e);
        }
        return new Entity(option);
    }
    return new Entity();
}

Response.ResponseBuilder resp_builder=Response.status(Response.Status.BAD_REQUEST);
resp_builder.entity(e.getMessage());//message you need as the body
throw new WebApplicationException(resp_builder.build());

public class CustomBadReq extends WebApplicationException {
     public CustomBadReq(String message) {
         super(Response.status(Response.Status.BAD_REQUEST)
             .entity(message).type(MediaType.TEXT_PLAIN).build());
     }
}

String msg = e.getMessage();
throw new BadRequestException(Response.status(BAD_REQUEST)
                .entity(msg).build());