How to force restful responses in json? - yii2

Question

I want to add some api to my Yii2 site. Api must be only in json. I don't want to set Accept: application/json headers for each request. I can set 'response' => ['format' => \yii\web\Response::FORMAT_JSON] in application configuration but it breaks all pages. Also my api function returns data in xml.
I tried to use rest\ActiveRecord for my purposes. Maybe I do it's wrong. What I want.
To have my Yii2 based site with some api acсessed through https://example.com/api/controller/action. In project I want to see folder controllers/api which contains my controllers. Controllers must use standard \yii\db\ActiveRecord based models. Also controllers input paramaters only in json body or as part url and output data only in json.

Answer 1

You may need to set the following code in the controller's action somewhere before return or in beforeAction() method:
\Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
also since Yii 2.0.11 there is a dedicated asJson() method to return a response in JSON format:
return $this->asJson($array);

Answer 2

The more elegant solution is to use yii\filters\ContentNegotiator.
When the Accept header is missing ContentNegotiator assumes it allows any type and send response in first format defined in its $formats property. If the requested format is not among accepted formats the content negotiator will throw yii\web\NotAcceptableHttpException and app will respond with http status 406 Not Acceptable.
You can add it in your controller in behaviors() method like this:
public function behaviors()
{
return [
[
'class' => 'yii\filters\ContentNegotiator',
'formats' => [
'application/json' => \yii\web\Response::FORMAT_JSON,
],
],
];
}
If your controller extends yii\rest\Controller it already has the ContentNegotiator filter added among its behaviors. You only need to limit allowed formats like this:
public function behaviors()
{
$behaviors = parent::behaviors();
$behaviors['contentNegotiator']['formats'] = [
'application/json' => \yii\web\Response::FORMAT_JSON,
];
return $behaviors;
}
Using ContentNegotiator instead of explicitly forcing the JSON format in beforeAction() will allow for easier addition of other formats if they are needed in future.