Magento 2 Action allow the developers using $request $response and $resultRedirectFactory  objects without injecting (DI) by hand .
By extending \Magento\Backend\App\Action for backend action case or \Magento\Framework\App\Action\Action for global case , you have $request $response and $resultRedirectFactory .

1 – Request :

the top level parent class of action is Magento\Framework\App\Action\AbstractAction ,  AbstractAction injected by di with \Magento\Framework\App\Action\Context $context .
 

 
    public function __construct(
        \Magento\Framework\App\Action\Context $context
    ) {
        $this->_request = $context->getRequest();
        $this->_response = $context->getResponse();
        $this->resultRedirectFactory = $context->getResultRedirectFactory();
        $this->resultFactory = $context->getResultFactory();
    }
 

 
    /**
     * Retrieve request object
     *
     * @return \Magento\Framework\App\RequestInterface
     */
    public function getRequest()
    {
        return $this->_request;
    }
 
    /**
     * Retrieve response object
     *
     * @return \Magento\Framework\App\ResponseInterface
     */
    public function getResponse()
    {
        return $this->_response;
    }
 

Ok inside your action you can get it :
$request = $this->getRequest() ;
the request object give you many method you can find inside interface RequestInterface  :
 

 
    public function getModuleName();
    public function setModuleName($name);
    public function getActionName();
    public function setActionName($name);
    public function getParam($key, $defaultValue = null);
    public function setParams(array $params);
    public function getParams();
    public function getCookie($name, $default);
    public function isSecure();
  

Example of how use:

A - ok imagine we want restrict the access to categories by customer group and we want execute a code just if we point in the specific module :
 

 
     if($request->getModuleName()  == “Magento_Catalog”)
    {
      //you code
    }
 

B – get value of parameter in url :
 

 
     $id = $request-> getParam(“id”,0);
 

C – forward to other module controller and action (this method isusefulin unit test):
 

 
     $this->getRequest()->setModuleName($currentModuleName);
     $this->getRequest()->setControllerName($currentControllerName);
     $this->getRequest()->setActionName($currentActionName);
 

But for almost for full stack method you need open Magento\Framework\App\Request\Http because Magento 2 when you  call RequestInterface  give you with preference  Http class as result .

2 – Response :

Ok see :
    <preference for="Magento\Framework\App\ResponseInterface" type="Magento\Framework\App\Response\Http" />

A – Return Json Content:
 

 
return $this->getResponse()->representJson($this->jsonHelper->jsonEncode($response_array));
 

the $this->jsonHelper is instance of \Magento\Framework\Json\Helper\Data you can injected by DI

B – Append content to body :
 

 
$this->getResponse()->appendBody($this->jsonHelper->jsonEncode($data));
 

C – Public and private cache :
you can use two method for that :
setPrivateHeaders($ttl) and setPublicHeaders($ttl) ;
$ttl :is int variable represent max-age and expire date by second
To handle this situation, every response may be set to be public or private:
public
Indicates that the response may be cached by both private and shared caches.
private
Indicates that all or part of the response message is intended for a single user and must not be cached by a shared cache.

3 – resultRedirectFactory :

Yes for redirect your page to other Url you can use :
 

 
$resultRedirect = $this->resultRedirectFactory->create();
$resultRedirect->setPath('customer/account/');
return $resultRedirect;