I created a page by using following way
Portal portal = PortalRequest.getInstance().getPortal();
Page newpage = portal.createPage(new PageId("classic", "mypage"));
newpage.setDisplayName("My New Page");
But now my problem is how to add portlet into that page?
No, not at the moment. We only support 'page meta data' and not the page layout which would include your applications (portlets). First we wanted to reduce scope so we could focus on full navigation API and second we wanted to use newly developed internal services like NavigationService and PageService; however, development has not been done to support the data you want internally.