How to get CustomFieldManager in WebWork class

[Jorge Jerez]

I have to show all custom fields objects in a template, I render this template with a webwork, so I have to get this fields there, how can i do it? 

public WebworkProvider(CustomFieldManager cfm) {
    //EMPTY CONSTRUCTOR
    List<CustomField> customFieldObjects = cfm.getCustomFieldObjects();
    names = new String[customFieldObjects.size()];
    for (int i = 0; i < customFieldObjects.size(); i++) {
        names[i] = customFieldObjects.get(i).getFieldName();
    }
}

I just tried that, but return a 404, I have another method for return that Array