Preserving model state with Post/Redirect/Get pattern

Question

At the moment I am trying to implement the Post/Redirect/Get pattern with Spring MVC 3.1. What is the correct way to preserve and recover the model data + validation errors? I k

Answer 1

public class BindingHandlerInterceptor extends HandlerInterceptorAdapter {

    public static final String BINDING_RESULT_FLUSH_ATTRIBUTE_KEY = BindingHandlerInterceptor.class.getName() + ".flashBindingResult";

    private static final String METHOD_GET = "GET";
    private static final String METHOD_POST = "POST";


    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {


        if(METHOD_POST.equals(request.getMethod())) {

            BindingResult bindingResult = getBindingResult(modelAndView);

            FlashMap outFlash = RequestContextUtils.getOutputFlashMap(request);

            if(bindingResult == null || ! bindingResult.hasErrors() || outFlash == null ) {
                return;
            }

            outFlash.put(BINDING_RESULT_FLUSH_ATTRIBUTE_KEY, bindingResult);

        }

        Map inFlash = RequestContextUtils.getInputFlashMap(request);

        if(METHOD_GET.equals(request.getMethod()) && inFlash != null && inFlash.containsKey(BINDING_RESULT_FLUSH_ATTRIBUTE_KEY)) {

            BindingResult flashBindingResult = (BindingResult)inFlash.get(BINDING_RESULT_FLUSH_ATTRIBUTE_KEY);

            if(flashBindingResult != null) {

                BindingResult bindingResult = getBindingResult(modelAndView);

                if(bindingResult == null) {
                    return;
                }

                bindingResult.addAllErrors(flashBindingResult);

            }

        }

    }

    public static BindingResult getBindingResult(ModelAndView modelAndView) {

        if(modelAndView == null) {
            return null;
        }

        for (Entry key : modelAndView.getModel().entrySet()) {
            if(key.getKey().startsWith(BindingResult.MODEL_KEY_PREFIX)) {
                return (BindingResult)key.getValue();
            }
        }

        return null;
    }


}