How to get output parameters in the Async Task?

Issue

Async task is being used for Service Task Execution, during this execution it is desired to retrieve Data Input and Output parameters (Result parameters) that have been defined for the task.

Using following code:

public class EJBCommand implements Command {

    public ExecutionResults execute(CommandContext ctx) throws Exception {

    Map data=ctx.getData();
    WorkItem workitem = data.get("workitem");
    Map parameters = workitem.getParameters();
    Map result = workitem.getResults();

The result returned an empty map. How to get data output keys that have been defined previously?