I am trying to learn Spring MVC recently. It seems that i did not understand well the functionalities of #ModelAttribute annotation and HttpSession.
#SessionAttributes({"shoppingCart", "count"})
public class ItemController {
#ModelAttribute("shoppingCart")
public List<Item> createShoppingCart() {
return new ArrayList<Item>();
}
#ModelAttribute("count")
public Integer createCount() {
return 0;
}
#RequestMapping(value="/addToCart/{itemId}", method=RequestMethod.GET)
public ModelAndView addToCart(#PathVariable("itemId") Item item,
#ModelAttribute("shoppingCart") List<Item> shoppingCart, #ModelAttribute("count") Integer count) {
if(item != null) {
shoppingCart.add(item);
count = count + 1;
}
return new ModelAndView(new RedirectView("showAllItems")).addObject("count", count);
}
#RequestMapping(value="/deleteFromCart/{itemId}", method=RequestMethod.GET)
public ModelAndView deleteFromCart(#PathVariable("itemId") Item item,
HttpSession session) {
List<Item> list = (List<Item>) session.getAttribute("shoppingCart");
list.remove(item);
//session.setAttribute("shoppingCart", list);
Integer count = (Integer) session.getAttribute("count");
count = count - 1;
session.setAttribute("count", count);
return new ModelAndView(new RedirectView("showAllItems"));
}
ShoppingCart and count are the session attributes.
The problem is in the deleteFromCart method. I get the count from session, reassign it and overwrite it in session. But i cant see the updated value of count on jsp. However, the updated shoppingCart object can be seen updated, although i do not overwrite the session object (since the object is the same object which is already in session).
But why is the count not updated, although i overwrite it with session.setAttribute?
When i add the new count object to the model (model.addObject("count", count)) then i can see the updated value of count. But why does not session.setAttribute give the same result?
First of all, #SessionAttribute does not have to use the http session. It uses a SessionAttributeStore which can have anything as its backing storage. Only the default implementation uses the http session.
The reason why your code does not work as expected lies in how #SessionAttribute works.
Before a controller method is invoked, everything listed in #SessionAttributes, in your case {"warenkorb", "count"}, is read from the session and added to the model.
After the method has returned the session is updated with everything that has been added to the model within the method.
.addObject("count", count)
-> count is added to the model and afterwards to the session.
session.setAttribute("count", count)
-> count is added to the session but not to the model. It will be added to the model before the next invocation of any controller method. But as for now the model still has the old count. And the model is what gets added to the request. And if an attribute can be found in the request scope then the jsp does not care about what's in the session.
When you use #SessionAttributesand #ModelAttribute (or Spring MVC in general) then avoid using HttpSession or HttpRequest. Even HttpResponseis of limited use. Embrace the beauty of Spring MVC instead :)
model.addObject puts object to the request scope while HTTPsession.setAttribute puts it to the session scope. And since variables on jsp are resolved on the next order: page scope -> request scope -> session scope -> application scope, you get what you get.
Java method params are passed by values. You can assign to this paramateter anything yoou want inside the method, but it won't have ny effect outside of it . Insisde of the method you're dealing with the copy of the param
Related
I am pretty new in Spring MVC and I have the following doubt about how correctly achieve the following task.
I am working on a web application that implement a user registration process. This registration process is divided into some consecutive steps.
For example in the first step the user have to insert a identification code (it is a code that identify uniquely a user on some statal administration systems) and in the second step it have to compile a form for his personal data (name, surname, birth date, and so on).
So, actually I have the following controller class that handle these steps:
#Controller
public class RegistrazioneController {
#Autowired
private LoadPlacesService loadPlacesService;
#RequestMapping(value = "/iscrizioneStep1")
public String iscrizioneStep1(Model model) {
return "iscrizioneStep1";
}
#RequestMapping(value = "/iscrizioneStep2", method=RequestMethod.POST)
public String iscrizioneStep2(Model model, HttpServletRequest request, #RequestParam("cf") String codicFiscale) {
System.out.println("INTO iscrizioneStep2()");
//String codicFiscale = request.getParameter("cf");
System.out.println("CODICE FISCALE: " + codicFiscale);
model.addAttribute("codicFiscale", codicFiscale);
return "iscrizioneStep2";
}
#RequestMapping(value = "/iscrizioneStep3", method=RequestMethod.POST)
public String iscrizioneStep3(#ModelAttribute("SpringWeb")Step2FormCommand step2Form, ModelMap model, HttpServletRequest request) {
System.out.println("INTO iscrizioneStep3()");
System.out.println("NOME: " + step2FormCommand.getName());
return "iscrizioneStep3";
}
Into the iscrizioneStep2() it is retrieved the first code (#RequestParam("cf") String codicFiscale).
Into the iscrizioneStep3() it is retrieved a command object containing the data inserted into the form of the view in which this form was submitted, this one:
#ModelAttribute("SpringWeb")Step2FormCommand step2FormCommand
It works fine.
Now my problem is that I have another object named Step3View that have to be initialized with the aggregation of the #RequestParam("cf") String codicFiscale object retrieved into the iscrizioneStep2() method and the #ModelAttribute("SpringWeb")Step2FormCommand step2FormCommand retrieved into the iscrizioneStep3() method.
This Step3View class simply contain the String codicFiscale and all the fields of the Step2FormCommand class.
Now my doubts are: what is the best way to handle this situation? Where have I to declare this Step3View object? at controller level? (so I can use it in all my controller methods?). Have I to annotate this class with #Component (or something like this) to inject it in my controller?
What is the best solution for this situation?
I think in order to get an answer you need to understand the question and ask the right question. I think your question is "how do I pass a parameter from one page to another page in SpringMVC?". You specifically want to know how to pass the "cf" param, but readers here will tend to pass over questions that are too specific because it takes too much time to figure out what you want.
In answer to that, see Spring MVC - passing variables from one page to anther as a possible help.
Also, there are many good answers about this question for JSP in general, which can be worked into the SpringMVC architecture. See How to pass value from one jsp to another jsp page? as a possible help.
For years I have been using #ModelAttribute to create and initialize my command object like so:
#RequestMapping()
public String someHandler(#ModelAttribute("formBean") FormBean formBean) {
// Do something
}
#ModelAttribute("formBean")
public FormBean createFormBean() {
FormBean formBean = new FormBean();
// Do some sort of initialization
return formBean;
}
In this example, I have a handler in a Controller that needs a FormBean, and a "create" method that gives it one if one isn't already in the Model (or session, if using #SessionAttributes). So, when my someHandler() method is ran, the FormBean is already there and populated because my createFormBean() had already ran.
However, my colleague is claiming that, although this works just fine, that I am misusing the #ModelAttribute for a purpose it wasn't intended for, namely in the creation of the Command object. In his interpretation from the JavaDoc, you should only use #ModelAttribute to create static data, like items used to populate a dropdown list or such.
I know this works for creating and initializing my Command object quite well, but am I using this for a purpose it was not originally intended for? Am I breaking some cardinal rule here?
#ModelAttribute("formBean")
public FormBean createFormBean() {
FormBean formBean = new FormBean();
// Do some sort of initialization
return formBean;
}
This can be useful if you need to initialize model attribute before binding form values from view. For example, you can query object from database (to get available it in current session).
In other cases I prefer to use this method:
#RequestMapping
public String someHandler(final Model model) {
FormBean formBean = new FormBean();
// Do some sort of initialization
model.addAttribute("formBean", formBean);
}
I think it more clear to understand. But I don't think that you "breaking some cardinal rule here".
I am trying to learn Spring MVC recently. It seems that i did not understand well the functionality of #SessionAttributes and #ModelAttribute annotations.
This is a part of my controller:
#SessionAttributes({"shoppingCart", "count"})
public class ItemController {
#ModelAttribute("shoppingCart")
public List<Item> createShoppingCart() {
return new ArrayList<Item>();
}
#ModelAttribute("count")
public Integer createCount() {
return 0;
}
#RequestMapping(value="/addToCart/{itemId}", method=RequestMethod.GET)
public ModelAndView addToCart(#PathVariable("itemId") Item item,
#ModelAttribute("shoppingCart") List<Item> shoppingCart, #ModelAttribute("count") Integer count) {
if(item != null) {
shoppingCart.add(item);
count = count + 2;
}
return new ModelAndView(new RedirectView("showAllItems"));
}
Basically there is a jsp listing all the items. Wenn user click "addToCart" for a specific item, this item will be added to the shoppingCart list. I better explain my understanding of this controller first and you can tell me what i do not get.
First time when the ItemController is called, the createShoppingCart and createCount methods will be executed and the return parameters will be saved in session under names "shoppingCart" and "count". When the user calls the url ".../addToCart/1", addToCart method will be called. Since i need there in the method signature 2 values from session, the controller will look in the session whether the values are already there. Yes they are.. At this time shoppingCart is an empty list, and count is 0. In the method body, the selected item will be added to list, count will be 2. The jsp will be displayed again.
The problem is, jsp can see that the list shoppingCart is now not empty. but the count is still 0. When i add Items to basket, I can see on jsp that the shoppingCart is filled with items, but the value of count is always 0.
Actually there is no any difference between shoppingCart and count objects.. i dont get it why it behaves like this. I first doubted that the count type was primitive int, then i changed it to Integer typ, still the problem is not solved.
You don't change count (You can't in fact), you assign to it. So the model still points to the old value. You would have to add the new value manually.
myModelAndView.add("count", count);
But why bothering with count if you can use warenkorb.size anyway?
My MVC action method receives an entity object (Page) that the default model binder creates from form collection data. Some of the fields are wrong or null because they were not sent in the request to the server, for example I do not send "CreateDate" and the default model binder sets this property to some default value which I don't need.
Once the object is attached it of course tries to persist all the values (including invalid/not needed ones to the database). I could of course assign manually on a per property basis but was wondering if maybe I can somehow flag a property so it is not persisted when EntityState is set to modified and SaveChanges() is called..
public ActionResult SomeMethod(Page page)
{
page.ModifyDate = DateTime.Now;
_db.NewsPages.Attach(page);
_db.ObjectStateManager.ChangeObjectState(page, System.Data.EntityState.Modified);
_db.SaveChanges();
_db.Dispose();
}
The correct way to handle this is using different class for view model, attach empty entity to the context and assign real values per property (or let AutoMapper to handle this scenario) as #Darin suggested in the comment.
If you want to go your way you must not change state of the POCO entity but you must change state of every changed property:
public ActionResult SomeMethod(Page page)
{
page.ModifyDate = DateTime.Now;
_db.NewsPages.Attach(page);
ObjectStateEntry entry = _db.ObjectStateManager.GetObjectStateEntry(page);
entry.SetModifiedProperty("ChangedPropertyName");
// Do the same for all other changed properties
_db.SaveChanges();
_db.Dispose();
}
What is the method to refresh data on subsequent pages - second page, third page, etc - of a Primefaces dataTable using the LazyDataModel method?
Also, if I select an item in a dataTable to view its detail on another page, then came back to the dataTable using either the browser's Back button or implement JavaScript's history.back() method, it seems that the dataTable always reset its position to the first page instead of going back to the page the user was on. How can I force the dataTable to stay on the last viewed page?
My codes for lazy loading are:
private final class LazyLoader extends LazyDataModel<BookModel>
{
private static final long serialVersionUID = 1L;
public LazyLoader(String sort, String category, String operator, String input) {
setListing(getBookService().getListing(sort, category, operator, input));
}
#Override
public List<BookModel> load(int first, int pageSize, String sortField, boolean sortOrder, Map<String, String> filters) {
return getListing();
}
}
And for the Submit method is:
public String Submit()
{
sort = sortBean.getSort();
category = categoryBean.getCategory();
operator = operatorBean.getOperator();
input = searchBean.getInput();
lazyModel = new LazyLoader(sort, category, operator, input);
lazyModel.setRowCount(listing.size());
return null;
}
I'm using #ViewScoped for listing the book records as well as showing detail of a book record.
Does anyone has similar issues with Primefaces dataTable?
Keep using #ViewScoped. You should not use #SessionScoped unless you have real needs for it.
To remember the last page, you have to set the first attribute of the load method. You can do that with request parameters. Something like: yourview.xhtml?f=3 .
About the refreshing, the thing is that you are using a lazy loader but you're loading everything at once... Your load method is the one that should do the query on demand, that is, page by page.
Does pagination work for you without lazy loading? I would verify that works as expected before you jump into the hardest case.
If you want your dataTable to remember the last pagination after you navigate away from the JSF page then you need to make your managed bean SessionScoped. The lifecycle of the ViewScoped managed bean ends after navigation leaves the view.
In order to keep the selected page you have to do 2 things.
First make the managedBean session scoped.
Second set a binding between the datatable and a UIData object. In your backend bean for example put
private UIData filasUIData = null;
public UIData getFilasUIData() {
return filasUIData;
}
public void setFilasUIData(UIData filasUIData) {
this.filasUIData = filasUIData;
}
Now in your data table
<ice:dataTable
binding="#{yourBean.filasUIData}"
that´s all.