RetrievePaymentCommandAdapter.java

public class RetrievePaymentAdapter implements JavaDelegate {

  public void execute(ActivityExecution ctx) {    
    // prepare message content, you can load variables from persistent flow context
   ctx.getVariable("orderId");
    // ...

    // Send command
    publishCommand("DoPayment", payload);
      // ant tell the engine to wait for the next event 
    addEventSubscription("PaymentReceived", ctx);
  }

}