和Spring其他框架一样，对于webflow,Spring也提供了2个系列，一个是servlet级别的webflow,它在org.springframework.webflow.mvc.servlet 包中,一个是portlet级别的webflow,它在org.springframework.webflow.mvc.portlet包中，我们这里讨论portlet级别的FlowHandler。
FlowHandlerAdapter,正如Spring官方注释所说的，它将特定的flow定义文件关联到Flow Handler上。它实现了HandlerAdaptor接口，这个接口的作用是让Spring的DispatcherPortlet对应各种类型的request(比如actionRequest,resourceRequest,renderRequest,event)可以用特定的Handler来进行处理。这个接口定义了如下方法：
publicinterface HandlerAdapter {
boolean supports(Object handler);
void handleAction(ActionRequest request, ActionResponse response, Object handler) throws Exception;
ModelAndView handleRender(RenderRequest request, RenderResponse response, Object handler) throws Exception;
ModelAndView handleResource(ResourceRequest request, ResourceResponse response, Object handler) throws Exception;
void handleEvent(EventRequest request, EventResponse response, Object handler) throws Exception;
}
那么如何处理呢，在FlowHandlerAdapter中给出了对应的实现，我们以render为例，它的代码如下：
public ModelAndView handleRender(RenderRequest request, RenderResponse response, Object handler) throws Exception {
FlowHandler flowHandler = (FlowHandler) handler;
checkAndPrepare(request, response);
populateConveniencePortletProperties(request);
FlowException e = clearActionRequestFlowException(request, response, flowHandler);
if (e != null) {
return handleException(e, flowHandler, request, response);
}
String flowExecutionKey = flowUrlHandler.getFlowExecutionKey(request);
if (flowExecutionKey != null) {
return resumeFlowRender(request, response, flowHandler, flowExecutionKey);
} else {
MutableAttributeMap input = flowHandler.createExecutionInputMap(request);
if (input == null) {
input = defaultCreateFlowExecutionInputMap(request);
}
return startFlowRender(flowHandler, input, request, response);
}
}
从这里我们可以看出，它在第2行中从参数获得FlowHandler对象，在3行做初始化工作，第4行从render request中填出必要的Portlet属性。