Spring Portlet中的webflow

和Spring其他框架一樣，對於webflow,Spring也提供了2個系列，一個是servlet級別的webflow,它在org.springframework.webflow.mvc.servlet 包中,一個是portlet級別的webflow,它在org.springframework.webflow.mvc.portlet包中，我們這裡討論portlet級別的FlowHandler。

FlowHandlerAdapter,正如Spring官方注釋所說的，它將特定的flow定義文件關聯到Flow Handler上。它實現了HandlerAdaptor接口，這個接口的作用是讓Spring的DispatcherPortlet對應各種類型的request(比如actionRequest,resourceRequest,renderRequest,event)可以用特定的Handler來進行處理。這個接口定義了如下方法：

1. publicinterface HandlerAdapter {
2. boolean supports(Object handler);
3. void handleAction(ActionRequest request, ActionResponse response, Object handler) throws Exception;
4. ModelAndView handleRender(RenderRequest request, RenderResponse response, Object handler) throws Exception;
5. ModelAndView handleResource(ResourceRequest request, ResourceResponse response, Object handler) throws Exception;
6. void handleEvent(EventRequest request, EventResponse response, Object handler) throws Exception;
7. }

那麼如何處理呢，在FlowHandlerAdapter中給出了對應的實現，我們以render為例，它的代碼如下：

1. public ModelAndView handleRender(RenderRequest request, RenderResponse response, Object handler) throws Exception {
2. FlowHandler flowHandler = (FlowHandler) handler;
3. checkAndPrepare(request, response);
4. populateConveniencePortletProperties(request);
5. FlowException e = clearActionRequestFlowException(request, response, flowHandler);
6. if (e != null) {
7. return handleException(e, flowHandler, request, response);
8. }
9. String flowExecutionKey = flowUrlHandler.getFlowExecutionKey(request);
10. if (flowExecutionKey != null) {
11. return resumeFlowRender(request, response, flowHandler, flowExecutionKey);
12. } else {
13. MutableAttributeMap input = flowHandler.createExecutionInputMap(request);
14. if (input == null) {
15. input = defaultCreateFlowExecutionInputMap(request);
16. }
17. return startFlowRender(flowHandler, input, request, response);
18. }
19. }

從這裡我們可以看出，它在第2行中從參數獲得FlowHandler對象，在3行做初始化工作，第4行從render request中填出必要的Portlet屬性。