Retrieve Data Using Apex Code with Viewer

Overview: use Apex (Callable interface) to return JSON data to Viewer templates.

Basic steps:

1. Create an Apex class implementing Callable.
2. Return a valid JSON object.
3. Update "External Data Class Name" in your template to the Apex API name.

Best practices: follow Salesforce Apex limits, write tests, and keep code lean.

Example Apex (simplified)

GetDataPluginExt.cls

global with sharing class GetDataPluginExt implements Callable {
	public Object call(String action, Map<String, Object> args) {
		Map<String, Object> input = (Map<String, Object>) args.get('input');
		Map<String, Object> output = (Map<String, Object>) args.get('output');
		Map<String, Object> options = (Map<String, Object>) args.get('options');
		return invokeMethod(action, input, output, options);
	}

	private Object invokeMethod(String methodName, Map<String, Object> inputMap, Map<String, Object> outMap, Map<String, Object> options) {
		switch on methodName {
			when 'getData' {
				String APIUrl = 'https://dummyjson.com/products/' + String.valueOf(Integer.valueOf(Math.round(Math.random()*30)));
				HttpRequest req = new HttpRequest();
				req.setEndpoint(APIUrl);
				req.setMethod('GET');
				req.setHeader('Content-Type', 'application/json');
				req.setTimeout(120000);
				HTTPResponse res = new Http().send(req);
				Map<String, Object> objectsList = (Map<String, Object>) JSON.deserializeUntyped(res.getBody());
				if (objectsList == null) return null;
				return objectsList;
			}
			when else {
				return '';
			}
		}
	}
}

You must return a valid JSON-serializable object that Viewer can consume.