如何在cakephp 3.x中的插件中检索会话值

Question

I integrated "blueimp" image uploader in CakePHP 3, I put "imagehandler" in plugin folder who is responsible for uploading and all other actions. it is working perfectly but I need to access user_id from Session in "imageHandler" (plugin file) but I could not get it. I did it like this

include('../plugins/UploadHandler.php');  
$upload_handler = new UploadHandler(); 

It works but I learned from SO that I need to pass $this argument if i need to access session in plugin file like this.

$upload_handler = new UploadHandler($this);

In initiliaze function of this file, I tried to read it. but other code use $this give error.

But code in "UploadHandler" file gives the error.
can you suggest any idea how I can access session value in plugin file.