Using a HandlerInterceptor to add model attributes with Spring Web Flow - spring-mvc

Question

I have a HandlerInterceptor to add some "global" model variables. It works.
Now, I try to reuse it in Spring Web Flow, for the same reason.
But HandlerInterceptors have the ModelAndView parameter set to NULL under Spring Web Flow (couldn't figure why, but it's a fact).
I have referenced my interceptor in the FlowHandlerMapping bean :
<bean class="org.springframework.webflow.mvc.servlet.FlowHandlerMapping">
<property name="order" value="0" />
<property name="flowRegistry" ref="flowRegistry" />
<property name="interceptors">
<list>
<ref bean="myInterceptor" />
</list>
</property>
</bean>
How can I add variables to the model ?
Is there a workaround, with the request parameter for example ?

Answer 1

Starting with Spring Webflow 2, the ModelAndView object is not generated anymore (see this post (and thread) at the SpringSource forum).
The FlowHandlerAdapter handle() function does not generate a ModedAndView anymore (it just returns null) even if this function is :
public ModelAndView handle(HttpServletRequest request,
HttpServletResponse response, Object handler)
So overriding this function is pointless, but this function creates a ServletExternalContext object, which holds all the flow variable, by calling its method :
protected ServletExternalContext createServletExternalContext(
HttpServletRequest request, HttpServletResponse response)
By overriding this function you can pretty much do what you want with this flow variables.
To do this, just create a class that extends FlowHandlerAdapter, register it instead of FlowHandlerAdapter and override the createServletExternalContext function.
Basically you use ServletExternalContext.getSessionMap() to access a SharedAttributeMap and register your properties.
As you have access to the HttpServletRequest and HttpServletResponse objects, this method can act petty much like a HandlerInterceptorAdapter.postHandle function.
See an example below.
I left out how to use generic way to reuse the same code for a HandlerInterceptor for the MVC and this object but it's easy to code, by implementing HandlerInterceptor.
MyFlowHandlerAdapter :
package my.package;
public class MyFlowHandlerAdapter extends FlowHandlerAdapter {
#Override
protected ServletExternalContext createServletExternalContext(
HttpServletRequest request,
HttpServletResponse response) {
ServletExternalContext context =
super.createServletExternalContext(request,response);
context.getSessionMap().put("myproperty", "myvalue");
return context;
}
}
You have the FlowHandlerAdapter object defined in you webflow-context.xml file like that :
<bean class="org.springframework.webflow.mvc.servlet.FlowHandlerAdapter">
<property name="flowExecutor" ref="flowExecutor"/>
</bean>
Just replace it with :
<bean class="my.package.MyFlowHandlerAdapter">
<property name="flowExecutor" ref="flowExecutor"/>
</bean>

Answer 2

ModelAndView can be null when the interceptor is processing an Ajax request.
Just check if ModelAndView is null. If not, that's because the interceptor is processing a view-model, so you can add your variables at this time.