How to create custom observers in magento2

In this blog We are going to explain you how to create your own custom event (observer) in magento2. For this firstly we declare a event whenever we want like I am going to declare this observer in controller execute method-

Step 1- Declaration of observer

public function execute()
    {
        try{
            if($this->getRequest()->isPost()){
                if (!$this->_formKeyValidator->validate($this->getRequest())) {
                    return $this->resultRedirectFactory->create()->setPath('*/*/');
                }
                ..

                /* Here want to create to execute some code whenever this controller will be executed - So we create custom event here */

                $this->_eventManager->dispatch(
                    'custom_observer_name',
                    [$this->getRequest()->getParams()]
                );

                ..
            }            
        }catch (\Magento\Framework\Exception\LocalizedException $e) {
            $this->messageManager->addError($e->getMessage());
            return $this->resultRedirectFactory->create()->setPath('*/*/');
        }  catch (Exception $e) {
            $this->messageManager->addError($e->getMessage());
            return $this->resultRedirectFactory->create()->setPath('*/*/');
        }
    }

Step 2- Calling the custom observer

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="custom_observer_name">
        <observer name="custom_observer_method" instance="Webkul\Grid\Observer\CustomObserverMethod"/>
    </event>
</config>

Step 3- creating custom observer method

namespace Webkul\Grid\Observer;

use Magento\Framework\Event\ObserverInterface;

class CustomObserverMethod implements ObserverInterface
{
    /**
     * custom event handler
     *
     * @param \Magento\Framework\Event\Observer $observer
     * @return void
     */
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        try{
            $eventData = $observer->getData();
            // Write your code here
        }catch(Exception $e){
            $this->messageManager->addError($e->getMessage());
        }
    }
}

So in this way you can create and call your own custom event easily.