AliasManager::getAliasByPath

public AliasManager::getAliasByPath($path, $langcode = NULL)

public function getAliasByPath($path, $langcode = NULL) {
  if ($path[0] !== '/') {
    throw new \InvalidArgumentException(sprintf('Source path %s has to start with a slash.', $path));
  }
  // If no language is explicitly specified we default to the current URL
  // language. If we used a language different from the one conveyed by the
  // requested URL, we might end up being unable to check if there is a path
  // alias matching the URL path.
  $langcode = $langcode ? : $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_URL)->getId();

  // Check the path whitelist, if the top-level part before the first /
  // is not in the list, then there is no need to do anything further,
  // it is not in the database.
  if ($path === '/' || !$this->whitelist->get(strtok(trim($path, '/'), '/'))) {
    return $path;
  }

  // During the first call to this method per language, load the expected
  // paths for the page from cache.
  if (empty($this->langcodePreloaded[$langcode])) {
    $this->langcodePreloaded[$langcode] = TRUE;
    $this->lookupMap[$langcode] = array();

    // Load the cached paths that should be used for preloading. This only
    // happens if a cache key has been set.
    if ($this->preloadedPathLookups === FALSE) {
      $this->preloadedPathLookups = array();
      if ($this->cacheKey) {
        if ($cached = $this->cache->get($this->cacheKey)) {
          $this->preloadedPathLookups = $cached->data;
        }
        else {
          $this->cacheNeedsWriting = TRUE;
        }
      }
    }

    // Load paths from cache.
    if (!empty($this->preloadedPathLookups[$langcode])) {
      $this->lookupMap[$langcode] = $this->storage->preloadPathAlias($this->preloadedPathLookups[$langcode], $langcode);
      // Keep a record of paths with no alias to avoid querying twice.
      $this->noAlias[$langcode] = array_flip(array_diff_key($this->preloadedPathLookups[$langcode], array_keys($this->lookupMap[$langcode])));
    }
  }

  // If we already know that there are no aliases for this path simply return.
  if (!empty($this->noAlias[$langcode][$path])) {
    return $path;
  }

  // If the alias has already been loaded, return it from static cache.
  if (isset($this->lookupMap[$langcode][$path])) {
    return $this->lookupMap[$langcode][$path];
  }

  // Try to load alias from storage.
  if ($alias = $this->storage->lookupPathAlias($path, $langcode)) {
    $this->lookupMap[$langcode][$path] = $alias;
    return $alias;
  }

  // We can't record anything into $this->lookupMap because we didn't find any
  // aliases for this path. Thus cache to $this->noAlias.
  $this->noAlias[$langcode][$path] = TRUE;
  return $path;
}