Get Web Service

//GET: Retrieve data or resources from Salesforce.
    
    // Method to asynchronously retrieve contacts from an external service
    @future(callout=true)
    public static void getContacts() {
        // Instantiate HTTP request and response objects
        HttpRequest req = new HttpRequest();
        HttpResponse response = new HttpResponse();
        
        try {
            // Set up HTTP request parameters
            // SourceOrgNamedCredential is your SourceORG Named Credential
            req.setEndpoint('callout:SourceOrgNamedCredential/services/apexrest/Contact/');
            req.setHeader('Content-Type', 'application/json; charset=UTF-8');
            req.setHeader('Accept', 'application/json');
            req.setMethod('GET');
            
            // Send HTTP request
            Http http = new Http();
            response = http.send(req);
            
            // Check if response is successful
            if (response.getStatusCode() == 200) {
                // Log successful retrieval of contacts
                System.debug('Contacts successfully retrieved.');
                System.debug('Response Body: ' + response.getBody());
            } else {
                // Log failure to retrieve contacts
                System.debug('Failed to retrieve contacts. Status code: ' + response.getStatusCode());
                System.debug('Response Body: ' + response.getBody());
            }
        } catch (Exception e) {
            // Log any exceptions that occur during the process
            System.debug('Exception occurred while retrieving contacts: ' + e.getMessage());
        }
    }