code: public static Flow perform(ServletRewrite<?, ?> event, EvaluationContext context, Flow subflow,
              SubflowTask subflowTask)
     {
        Flow flow = event.getFlow();
        try
        {
           event.setFlow(subflow);
           subflowTask.performInSubflow(event, context);
           return event.getFlow();
        }
        finally
        {
           event.setFlow(flow);
        }
     }
docs: Perform the given {@link SubflowTask} using the given {@link ServletRewrite} event initialized with a new
  {@link ServletRewriteFlow}. The original {@link ServletRewriteFlow} will be restored after task completion.
  
  @param event the {@link ServletRewrite} event used in the given {@link SubflowTask}
  @param subflow the {@link ServletRewriteFlow} to be us as the initial state for the given {@link SubflowTask}
  
  @return the resultant {@link ServletRewriteFlow} from the {@link SubflowTask} execution.