How to Call Apex Class Methods from a Custom Button or Link Using Visualforce

Step 1: Create the Visualforce Page

Create a Visualforce page that uses the standard controller of the target object (for example, Case) and an Apex extension class. Set the action attribute to reference the Apex method to be called on page load.
Key elements of the Visualforce page:

• standardController="Case" — binds the page to the Case object so that the Case record ID is automatically available
• extensions="EscalCase" — references the Apex class that extends the standard controller
• action="{!caseEscalation}" — calls the caseEscalation() method in the Apex extension class when the page loads
• The <apex:inputHidden> tag is used to pass the Case OwnerId to the Apex class

<apex:page standardController="Case" extensions="EscalCase" action="{!caseEscalation}">
<apex:form>
<apex:inputHidden value="{!case.OwnerId}"/>
</apex:form>
</apex:page>

Step 2: Create the Apex Controller Extension

The Apex extension class receives the standard controller in its constructor, retrieves the current Case record, and contains the business logic in the action method.
Key elements of the Apex class:

• The constructor EscalCase(ApexPages.StandardController controller) accepts the standard controller and retrieves the Case record
• The caseEscalation() method contains the custom business logic and returns a PageReference to redirect the user back to the Case record page
• The method uses setRedirect(true) on the PageReference to ensure a proper page redirect after processing

public class EscalCase {
    //Apex properties or variables

    public Id owner {get; set;}
    public Id Id { get; set; }
    public Case cas { get; set; }

    //constructor to get the Case record
    public EscalCase(ApexPages.StandardController controller) {
    cas =  (Case) controller.getRecord();
    Id = cas.Id;
    System.debug('The case record: ' + cas);
    owner = cas.OwnerId;
    }

    //Method that can is called from the Visual Force page action attribute
    public PageReference caseEscalation() {
       System.debug('Case Owner: ' + owner);
        System.debug('Case Id: ' + Id);
        //build your code logic here
       PageReference pageRef = new PageReference('/'+Id);
        pageRef.setRedirect(true);
       return pageRef; //Returns to the case page
    }
}