How to use the ocrd.validator.JsonValidator function in ocrd

def __init__(self, schema, validator_class=Draft4Validator):
        self.validator = validator_class(schema)

    def validate(self, obj):
        report = ValidationReport()
        if not self.validator.is_valid(obj):
            for v in self.validator.iter_errors(obj):
                report.add_error("[%s] %s" % ('.'.join(str(vv) for vv in v.path), v.message))
        return report

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class ParameterValidator(JsonValidator):

    def __init__(self, ocrd_tool):
        # TODO grep required properties
        required = []
        p = ocrd_tool['parameters']
        for n in p:
            if 'required' in p[n]:
                if p[n]['required']:
                    required.append(n)
                del(p[n]['required'])
        super(ParameterValidator, self).__init__({
            "type": "object",
            "required": required,
            "properties": p
        }, DefaultValidatingDraft4Validator)

def validate_json(obj, schema):
        if isinstance(obj, str):
            obj = json.loads(obj)
        return JsonValidator(schema).validate(obj)

def validate_json(obj, schema=OCRD_TOOL_SCHEMA):
        return JsonValidator.validate_json(obj, schema)

if 'required' in p[n]:
                if p[n]['required']:
                    required.append(n)
                del(p[n]['required'])
        super(ParameterValidator, self).__init__({
            "type": "object",
            "required": required,
            "properties": p
        }, DefaultValidatingDraft4Validator)


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class OcrdToolValidator(JsonValidator):

    @staticmethod
    def validate_json(obj, schema=OCRD_TOOL_SCHEMA):
        return JsonValidator.validate_json(obj, schema)

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class WorkspaceValidator(object):
    """
    Validates an OCR-D/METS workspace against the specs.

    Args:
        resolver (:class:`Resolver`) : Instance of a resolver
        mets_url (string) : URL of the METS file