Spring MVC @RequestParam和@SessionAttribute

Question

I'm new to Spring and Portlet development.

I'm using the spring-webmvc-portlet but I think the workflow is almost the same with servlets.

My use case is pretty common but it's still a bit of a struggle to make everything work the way i would like to.

I got a controller like this :

@Controller
@RequestMapping(value = "VIEW")
@SessionAttributes(value = "persons")
public class MyController

// Display a list of person in personList.jsp
@RenderMapping(params = "actionPerson=query")
public String showList() {
  return "personList";
}

@ActionMapping(params = "actionPerson=query"){

  // Here is a trick I use to avoid the MissingPortletRequestParameterException
  // to be raised 
  response.setRenderParameter("query","")
  response.setRenderParameter("actionPerson","query");
}

// Return a list of person and store it in the model
@ModelAttribute("persons")
public List<Person> getPersons(@RequestParam(value="query") String query) {
  List<Person> personList = personService.SearchByName(query);
  return personList;
}

So far i understand that methods annoted with @ModelAttribute are invoked every time to generate the model before any rendering process.

I don't want this method to invoked every time. I tried to use the annotation @SessionAttributes to store my list of person in the handler's conversational state.

My problem is the annotation @RequestParam raise the following expection :

org.springframework.web.portlet.bind.MissingPortletRequestParameterException: Required String parameter 'query' is not present
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter$PortletHandlerMethodInvoker.raiseMissingParameterException(AnnotationMethodHandlerAdapter.java:559)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveRequestParam(HandlerMethodInvoker.java:514)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveHandlerArguments(HandlerMethodInvoker.java:353)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:155)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:369)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.doHandle(AnnotationMethodHandlerAdapter.java:356)
at org.springframework.web.portlet.mvc.annotation.AnnotationMethodHandlerAdapter.handleRender(AnnotationMethodHandlerAdapter.java:296)
at org.springframework.web.portlet.DispatcherPortlet.doRenderService(DispatcherPortlet.java:764)
at org.springframework.web.portlet.FrameworkPortlet.processRequest(FrameworkPortlet.java:537)
at org.springframework.web.portlet.FrameworkPortlet.doDispatch(FrameworkPortlet.java:483)
at javax.portlet.GenericPortlet.render(GenericPortlet.java:248)

My guess is even if the method getPersons is not invoked. The @RequestParam(value="query) is still evaluated.

When I display my list of person, users can select a person to get detailed informations. I would like them to go back to the list of result without submitting a new query.

How can i handle this case properly ? Is there a way to skip @RequestParam to be evaluated ?

Thanks !

Answer 1

You could make @RequestParam as not required . This would allow your request to succeed, but query would then be null.

@ModelAttribute("persons")
public List<Person> getPersons(@RequestParam(value="query" , required=false) String query) {
  List<Person> personList = personService.SearchByName(query);
  return personList;
}

For more details on RequestParam