Question

We have a restlet server and client. We need to pass the error status and exception traces back to the client so that the client can take appropriate actions depending on the error status code. I read about StatusService and using response.setStatus() method but I can’t get the specific exceptions thrown during server side processing be displayed on client side. The DAO layer from the server throws specific DB related exceptions and status code such as (Unique key violation etc), which the client needs to see and take appropriate actions.

Also, what is the common way of doing this to have centralized error handling / processing on server and client side ? Filters ?

A brief example will really help.

Thanks,
Deep

Answer 1

You can only send HTTP status codes and optionally your own description message. You can also send a representation of the error by overriding the getRepresentation in the StatusService.

@Override
public Status getStatus(Throwable throwable, Resource resource) {
    Status ret = null;
    Throwable cause = throwable.getCause();
    if (cause == null) {
        Status status = super.getStatus(throwable, resource);
        ret = new Status(status, throwable.getMessage());
        log.log(Level.SEVERE, "Unexpected resource exception <" + ret.toString() + "> for throwable of type <" + throwable + "> at resource <" + resource + ">");
    } else if (cause instanceof NotFoundException) {
        ret = new Status(Status.CLIENT_ERROR_NOT_FOUND, cause, resource.getReference().toString());
        log.info("Not found <" + ret.toString() + "> for throwable of type <" + cause + "> at resource <" + resource + ">");
    } else if (cause instanceof ConstraintViolationsException) {
        ConstraintViolationsException e = (ConstraintViolationsException) cause;
        ret = new Status(Status.CLIENT_ERROR_BAD_REQUEST, cause, e.getViolations().iterator().next().getMessage());
        log.log(Level.SEVERE, "Constraint violation <" + e.getViolations().iterator().next().getMessage() + "> at resource <" + resource + ">");
    } else if (cause instanceof BusinessRuleException) {
        ret = new Status(Status.CLIENT_ERROR_BAD_REQUEST, cause, cause.getMessage());
        log.log(Level.SEVERE, "Business rule exception: <" + cause.getMessage() + "> at resource <" + resource + ">");
    } else {
        Status status = super.getStatus(throwable, resource);
        ret = new Status(status, throwable.getMessage());
        log.log(Level.SEVERE, "Unexpected server exception <" + ret.toString() + "> for throwable of type <" + throwable + "> at resource <" + resource + ">");
    }
    return ret;
}

@Override
public Representation getRepresentation(Status status, Request request, Response response) {
    String ret = "";
    if (status.getDescription() != null) {
        ret = status.getDescription();
    } else {
        ret = "unknown error";
    }
    return new StringRepresentation(ret, MediaType.TEXT_PLAIN);
}

You can return a representation of the error in getRepresentation in whatever format (XML, JSON, HTML) you want.