REST resource for validating gadget configuration

The REST resource that is used to validate the configuration parameters of a gadget should simply return a 200 OK status if the parameters are valid.

If the configuration is not valid, the REST resource should return a 400 Bad Request status with a JSON format body containing error messages.

Error messages may either be general (e.g. pointing out an inter-field consistency problem) or specific to the value of a particular field.

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{
    "errorMessages":
    {
        "start.date.before.end.date",
        "some.other.error"
    }
    "errors":
    {
        "field": "bugzillaUrl", "error": "gadget.bugzilla.invalid.url"
    }
}

Here's an example of Java JAXB annotated classes which produce suitable JSON:

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@XmlRootElement
public class ErrorCollection
{
    /**
     * Generic error messages
     */
    @XmlElement
    private Collection<String> errorMessages = new ArrayList<String>();

    /**
     * Errors specific to a certain field.
     */
    @XmlElement
    private Collection<ValidationError> errors = new ArrayList<ValidationError>();

    ...
}

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@XmlRootElement
public class ValidationError
{
    // The field the error relates to
    @XmlElement
    private String field;
    // The Error key...
    @XmlElement
    private String error;

    @XmlElement
    private Collection<String> params;

    ...
}

Creating a Gadget JavaScript Object