Using Grails 'respond' for HTML, JSON and XML responses

1_obvious_approach.groovy

def show(Widget widget){
    // renders a blank page for null objects
    respond widget, [model: [widget: widget]]
}

2_html_only.groovy

def show(Widget widget){
    if(!widget){
        // Pretty 404 page displayed, even for JSON requests
        response.sendError(404)
    }else{
        // Responds normally for non-empty, non-null objects
        respond widget, [model: [widget: widget]]
    }
}

3_working_html_json_xml.groovy

def show(Widget widget){
    if(!widget){
        // 404 status for all, pretty 404 page for users
        respond null, [status: 404, view: 'error404']
    }else{
        respond widget, [model: [widget: widget]]
    }
}

4_the_full_sausage.groovy

def show(Widget widget){
    if(!widget){
        def model = [ success: false, msg: [ code: 404, text: "The widget could not be found"]]
        // 404 status for all, JSON/XML/HTML appropriate response with detail
        respond model as Object, [model: model, status: 404, view: 'error404']
    }else{
        respond widget, [model: [widget: widget]]
    }
}