framework/web/UrlManager.php
public function init()
    {
        parent::init();

        if ($this->normalizer !== false) {
            $this->normalizer = Yii::createObject($this->normalizer);
            if (!$this->normalizer instanceof UrlNormalizer) {
                throw new InvalidConfigException('`' . get_class($this) . '::normalizer` should be an instance of `' . UrlNormalizer::className() . '` or its DI compatible configuration.');
            }
        }

        if (!$this->enablePrettyUrl) {
            return;
        }
        if (is_string($this->cache)) {
            $this->cache = Yii::$app->get($this->cache, false);
        }
        if (empty($this->rules)) {
            return;
        }
        $this->rules = $this->buildRules($this->rules);
    }
public function init()
    {
        parent::init();

        if ($this->normalizer !== false) {
            $this->normalizer = Yii::createObject($this->normalizer);
            if (!$this->normalizer instanceof UrlNormalizer) {
                throw new InvalidConfigException('`' . get_class($this) . '::normalizer` should be an instance of `' . UrlNormalizer::className() . '` or its DI compatible configuration.');
            }
        }

        if (!$this->enablePrettyUrl) {
            return;
        }
        if (is_string($this->cache)) {
            $this->cache = Yii::$app->get($this->cache, false);
        }
        if (empty($this->rules)) {
            return;
        }
        $this->rules = $this->buildRules($this->rules);
    }
Initializes UrlManager.