public function postStore(Request $request)
 {
     $existSite = Site::whereUser_id(Auth::id())->whereUrl($request->url);
     // 若站点已存在则更新站点
     if ($existSite->count()) {
         return self::postUpdate($request, $existSite->first()->id);
     }
     // 若站点不存在则存储站点
     $site = $request->all();
     $site['user_id'] = Auth::id();
     $tag = TagController::getCreate($request->tag);
     $site['tag_id'] = $tag->id;
     if (Site::create($site)) {
         return redirect('site/tag/' . $tag->name);
     }
     exit('书签保存失败');
 }