Symfony：从控制器外部读取parameter.yml

I Want to read a pareameter from parameters.yml. the solution is to extend the Controller but I got this error :

Error: Call to a member function getParameter() on null

I know that the container is null, but i don't know how to get the container?

class Configuration extends Controller
{
    public function __construct()
   {
     $this->tempFolderPath = sys_get_temp_dir();
     $parameter = $this->container->getParameter('a');
   }
}

Any solution ? Any help ?

this is not a best practice, but for me this is the only solution :( because in my code I have a static method that instantiate the hole class. so the solution will be.

public function __construct()
{
    $this->tempFolderPath = sys_get_temp_dir();
    global $kernel;
    $this->host = $kernel->getContainer()->getParameter('ws_host');
}

In classes which extend Controller calling $this->container->getParameter('a') is possible because of Container being injected into such classes. When you are in other class you need to inject parameter you want by defining your class as a service.

Your service definition will look something like:

services:
    class: App\Your\FooClass
    arguments:
        - %a%

Note % - it's special character to inject parameters

Then your class will look like:

class FooClass
{
    protected $a;

    public function __construct($a)
    {
        $this->a = $a;
        //you have your "a" parameter value injected into constructor
    }
}