I apologize in advance, admittedly I lack understanding in Wicket.
I read that using LoadableDetachableModel will prevent the object from being serialized, but after running the test several times I could see that it still gets serialized (after session timeout or on page load after timeout, sometimes). I think maybe I am not using models correctly. Any help or direction would be greatly appreciated.
the code looks like this:
...
LoadableDetachableModel ldm = new LoadableDetachableModel<SomeSettings>() {
#Override
public SomeSettings load() {
if (someSettingsDao == null) someSettingsDao = new SomeSettingsDao();
return someSettingsDao.Retrieve("1") == null ? new SomeSettings()
: (SomeSettings) someSettingsDao.Retrieve("1");
}
};
final Form<SomeSettings> form = new Form<SomeSettings>("someSettings", new CompoundPropertyModel<SomeSettings>(ldm)) {
private static final long serialVersionUID = 1L;
#Override
protected void onSubmit() {
if (someSettingsDao == null) someSettingsDao = new SomeSettingsDao();
if (someSettingsDao.Retrieve("1") != null)
someSettingsDao.Update(getModelObject());
else
someSettingsDao.Insert(getModelObject());
setResponsePage(UserPanel.someSettingsPageProvider.getPageClass());
}
};
...
Is it my use of models? Or how the data is persisted?
Thanks.
You are right. Data are persisted/serialized when Wicket decides to persist. After a component/page is rendered all components and models are detached. It means loadable detachable model detaches its inner model and there is nothing to be serialized. Of course serialization is made ever after page is rendered and it is not necessarry to keep it in memory.
Related
I am using a Message Driven Bean for storing messages in a list as you can see in the code given below:
/**
*
* #author sana-naeem
*/
#MessageDriven(mappedName = "jms/Queue-0", activationConfig = {
#ActivationConfigProperty(propertyName = "acknowledgeMode", propertyValue = "Auto-acknowledge"),
#ActivationConfigProperty(propertyName = "destinationType", propertyValue = "javax.jms.Queue")
})
public class MyMessageBean implements MessageListener{
private static ArrayList<String> list = new ArrayList<String>();
public MyMessageBean() {
}
#Override
public void onMessage(Message message) {
Textmessage msg = (TextMessage) message;
try {
if (message instanceof TextMessage) {
list.add("Messages: "+msg.getText());
} else {
System.out.println("No Text!!!");
}
} catch (JMSException ex) {
System.out.println("JMS.Exception....!!!");
}
}
public static ArrayList<String> getList() {
return list;
}
public void setList(ArrayList<String> list) {
this.list = new ArrayList<String>();
}
}
Now the problem is when I access the getter method from another Java Class; it is displaying list size=0;
Can I please know why is this happening;
I want to get that list in another Java Class;
If there is something wrong with the Queue, kindly let me know How to fix it???
It was working fine before;
Actually, previously I was using a Servlet to send messages but now, I am using a simple Java class with some initial context parameters defined...; so now the list is not working as expected...
Any advice or suggestion would be highly appreciable.
Thank you!
You shouldn't be using mutable static fields in an MDB. When you think MDB, think stateless, because that's how the container treats them. Here is a good reference;
http://www.coderanch.com/t/312086/EJB-JEE/java/Clarification-static-fields
Unfortunately, there isn't one single answer for your question. Without knowing anything about the rest of your application, how it is designed, what components you are using, how they interact, how it will be deployed, etc., it is difficult to give advice. But the first thing that comes to mind, given what limited information I have, is that you can create a separate object to wrap a Private ArrayList, and store a reference to that object in an appropriate context. Your MDB can then access that object. In that case, you'd have methods in the object to modify/read the ArrayList, and you'd synchronize these methods internally on the underlying ArrayList because the methods will be accessible by multiple threads.
But this is a brute force approach, not knowing anything else about your application. And depending on how your application is designed and deployed, this might not be the right advice. But the point here is that;
You need to separate your stateful object from what is intended to be a stateless object.
You need to make it accessible from an appropriate context.
You need to synchronize modify/read methods on the underlying POJO (ArrayList) if the containing object will be accessible by multiple threads.
how is said in the title I can not to resolve this problem for several hours. I hope I will get some useful replies, thank you.
wicket version: 1.5.7
public class EvalSearcherPage extends MenuPage {
...
private Code selectedEvalChoice;
...
...
RadioChoice<Code> evalRadioChoice = new RadioChoice<Code>("evalRadioChoice", new PropertyModel<Code>(this, "selectedEvalChoice"), EVAL_CHOICES, new ChoiceRenderer<Code>(getLocaleColumn()));
evalRadioChoice.add(new AjaxFormComponentUpdatingBehavior("onchange") {
private static final long serialVersionUID = 1L;
#Override
protected void onUpdate(AjaxRequestTarget target) {
...
target.add(...);
}
});
evalChoiceForm.add(evalRadioChoice);
...
in constructor:
EVAL_CHOICES is filled by choices,
selectedEvalChoice is filled by default choice
Everything works good till the moment when I want to select another choice. After that RadioChoice saves null to selectedEvalChoice.
So where is the problem, could anybody help, please?
Btw getter and setter are implemented for selectedEvalChoice but I learned that is not necessary.
For RadioChoice you have to use AjaxForm*Choice*ComponentUpdatingBehavior.
Check your log output, you should find a warning there.
Does anyone know for an example of GWT's CellTable using RequestFactory and that table is being edited? I would like to list objects in a table (each row is one object and each column is one property), be able to easily add new objects and edit. I know for Google's DynaTableRf example, but that one doesn't edit.
I searched Google and stackoverflow but wasn't able to find one. I got a bit confused with RF's context and than people also mentioned some "driver".
To demonstrate where I currently arrived, I attach code for one column:
// Create name column.
Column<PersonProxy, String> nameColumn = new Column<PersonProxy, String>(
new EditTextCell()) {
#Override
public String getValue(PersonProxy person) {
String ret = person.getName();
return ret != null ? ret : "";
}
};
nameColumn.setFieldUpdater(new FieldUpdater<PersonProxy, String>() {
#Override
public void update(int index, PersonProxy object, String value) {
PersonRequest req = FaceOrgFactory.getInstance().requestFactory().personRequest();
PersonProxy eObject = req.edit(object);
eObject.setName(value);
req.persist().using(eObject).fire();
}
});
and my code for data provider:
AsyncDataProvider<PersonProxy> personDataProvider = new AsyncDataProvider<PersonProxy>() {
#Override
protected void onRangeChanged(HasData<PersonProxy> display) {
final Range range = display.getVisibleRange();
fetch(range.getStart());
}
};
personDataProvider.addDataDisplay(personTable);
...
private void fetch(final int start) {
lastFetch = start;
requestFactory.personRequest().getPeople(start, numRows).fire(new Receiver<List<PersonProxy>>() {
#Override
public void onSuccess(List<PersonProxy> response) {
if (lastFetch != start){
return;
}
int responses = response.size();
if (start >= (personTable.getRowCount()-numRows)){
PersonProxy newP = requestFactory.personRequest().create(PersonProxy.class);
response.add(newP);
responses++;
}
personTable.setRowData(start, response);
personPager.setPageStart(start);
}
});
requestFactory.personRequest().countPersons().fire(new Receiver<Integer>() {
#Override
public void onSuccess(Integer response) {
personTable.setRowCount(response+1, true);
}
});
}
I try to insert last object a new empty object. And when user would fill it, I'd insert new one after it. But the code is not working. I says that user is "attempting" to edit a object previously edited by another RequestContext.
Dilemmas:
* am I creating too many context'es?
* how to properly insert new object into celltable, created on the client side?
* on fieldUpdater when I get an editable object - should I insert it back to table or forget about it?
Thanks for any help.
am I creating too many context'es?
Yes.
You should have one context per HTTP request (per fire()), and a context that is not fire()d is useless (only do that if you/the user change your/his mind and don't want to, e.g., save your/his changes).
You actually have only one context to remove here (see below).
Note that your approach of saving on each field change can lead to "race conditions", because a proxy can be edit()ed by at most one context at a time, and it remains attached to a context until the server responds (and once a context is fired, the proxy is frozen –read-only– also until the server responds).
(this is not true in all cases: when onConstraintViolation is called, the context and its proxies are unfrozen so you can "fix" the constraint violations and fire the context again; this should be safe because validation is done on the server-side before any service method is called).
how to properly insert new object into celltable, created on the client side?
Your code looks OK, except that you should create your proxy in the same context as the one you'll use to persist it.
on fieldUpdater when I get an editable object - should I insert it back to table or forget about it?
I'm not 100% certain but I think you should refresh the table (something like setRowData(index, Collections.singletonList(object)))
BTW, the driver people mention is probably the RequestFactoryEditorDriver from the Editor framework. It won't help you here (quite the contrary actually).
I am struggling with an issue using RequestFactory in GWT.
I have a User object : this object has login and password fields and other fields which are of collection type.
public class User {
private String login;
private String password;
private Set<Ressource> ressources;
// Getters and setters removed for brievety
}
I need to persist this object in db so I used RequestFactory because it seems like a CRUD-type operation to me.
Now for the RequestFactory part of the code, this is how I have tried to do it :
I create a UserRequestContext object to create a request object for the new User. Which gives something like :
public interface MyRequestFactory extends RequestFactory {
UserRequestContext userRequestContext();
RessourceRequestContext ressourceRequestContext();
}
and to create the user object I have something like this :
public class UserAddScreen extends Composite {
private UserProxy userProxy;
EventBus eventBus = new SimpleEventBus();
MyRequestFactory requestFactory = GWT.create(MyRequestFactory.class);
...
public UserAddScreen() {
...
requestFactory.initialize(eventBus);
}
public showUserAddScreen() {
// Textbox for password and login
// Listbox for ressources
}
}
I have tried to implement it as a wizard. So at the beginning of the UserAddScreen, I have a
a userProxy object.
This object fields are initialized at each step of the wizard :
the first step is adding the login and password
the second step is adding ressources to the userProxy object.
for this last step, I have two list boxes the first one containing the list of all the ressources i have in my DB table Ressources that I got from RessourceRequestContext.getAllRessource (I have a loop to display them as listbox item with the RessourceId as the value) and the second allows me to add the selected Ressources from this first listbox. Here is the first listbox :
final ListBox userRessourcesListBox = new ListBox(true);
Receiver<List<RessourceProxy>> receiver = new Receiver<List<RessourceProxy>>() {
#Override
public void onSuccess(List<RessourceProxy> response) {
for(RessourceProxy ressourceProxy : response) {
ressourcesListBox.addItem(ressourceProxy.getNom() + " " + ressourceProxy.getPrenom(), String.valueOf(ressourceProxy.getId()));
}
}
};
RessourceRequestContext request = requestFactory.ressourceRequestContext();
request.getAllRessource().fire(receiver);
So, as you can see, my code loops over the retrieved proxies from DB and initializes the items within the listbox.
Here are the control buttons :
final Button addButton = new Button(">");
addButton.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
for (int i = 0; i < ressourcesListBox.getItemCount(); i++) {
boolean foundInUserRessources = false;
if (ressourcesListBox.isItemSelected(i)) {
for (int j = 0; j < userRessourcesListBox
.getItemCount(); j++) {
if (ressourcesListBox.getValue(i).equals(
userRessourcesListBox.getValue(j)))
foundInUserRessources = true;
}
if (foundInUserRessources == false)
userRessourcesListBox.addItem(ressourcesListBox
.getItemText(i), ressourcesListBox
.getValue(i));
}
}
}
});
So when somebody selects one or more users and click on a ">" button, all the selected items go to the second listbox which is named userRessourceListBox
userRessourcesListBox.setWidth("350px");
userRessourcesListBox.setHeight("180px");
After that, I have a FINISH button, which loops over the items in the second listbox (which are the ones I have selected from the first one) and I try to make a request (again) with RequestFactory to retrieve the ressourceProxy object and initialize the userProxy ressources collection with the result
final Button nextButton = new Button("Finish");
nextButton.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
RessourceRequestContext request = requestFactory.ressourceRequestContext();
for(int i = 0; i < userRessourcesListBox.getItemCount(); i++) {
Receiver<RessourceProxy> receiver = new Receiver<RessourceProxy>() {
#Override
public void onSuccess(RessourceProxy response) {
userProxy.getRessource().add(response);
}
};
request.find(Long.parseLong(userRessourcesListBox.getValue(i))).fire(receiver);
}
creationRequest.save(newUserProxy).fire(new Receiver<Void>() {
#Override
public void onSuccess(Void response) {
Window.alert("Saved");
}
});
}
});
Finally, (in the code above) I try to save the UserProxy object (with the initial request context I have created userProxy with)... but it doesn't work
creationRequest.save(newUserProxy).fire(...)
It seems like when looping over the result in the onSuccess method :
userProxy.getRessource().add(response);
I retrieve the response (of type RessourceProxy) but beyond this method, for example when I try to save the userProxy object AFTER THE LOOP, there are no RessourceProxy objects in the ressourceProxy collection of userProxy...
Have you guys ever experienced something like this ?
Perhaps I am not doing it right : do I have to get the ressource with the UserRequestContext ? so that my newUser object and ressources are managed by the same request Context ?
if yes then I think it's a little bit weird to have something mixed together : I mean what is the benefit of having a Ressource-related operation in the User-related request context.
any help would be really really ... and I mean really appreciated ;-)
Thanks a lot
The message "… has been frozen" means that the object has been either edit()ed or passed as an argument to a service method, in another RequestContext instance (it doesn't matter whether it's of the same sub-type –i.e. UserRequestContext vs. RessourceRequestContext– or not) which hasn't yet been fire()d and/or the response has not yet come back from the server (or it came back with violations: when the receiver's onViolation is called, the objects are still editable, contrary to onSuccess and onFailure).
UPDATE: you have a race condition: you loop over the resource IDs and spawn as many requests as the number of items selected by the user, and then, without waiting for their response (remember: it's all asynchronous), you save the user proxy. As soon as you fire() that last request, the user proxy is no longer mutable (i.e. frozen).
IMO, you'd better keep the RessourceProxys retrieved initially and use them directly in the user proxy before saving it (i.e. no more find() request in the "finish" phase). Put them in a map by ID and get them from the map instead of finding them back from the server again.
If I run the following code it throws the following error:
An entity object cannot be referenced by multiple instances of IEntityChangeTracker
public void Save(Category category)
{
using(var db = new NorthwindContext())
{
if(category.CategoryID == 0)
{
db.AddToCategorySet(category);
}
else
{
//category.RemoveTracker();
db.Attach(category);
}
db.SaveChanges();
}
}
The reason is of course that the category is sent from interface which we got from GetById method which already attached the EntityChangeTracker to the category object. I also tried to set the entity tracker to null but it did not update the category object.
protected void Btn_Update_Category_Click(object sender, EventArgs e)
{
_categoryRepository = new CategoryRepository();
int categoryId = Int32.Parse(txtCategoryId.Text);
var category = _categoryRepository.GetById(categoryId);
category.CategoryName = txtUpdateCategoryName.Text;
_categoryRepository.Save(category);
}
I'm still learning Entity Framework myself, but maybe I can help a little. When working with the Entity Framework, you need to be aware of how you're handling different contexts. It looks like you're trying to localize your context as much as possible by saying:
public void Save(Category category)
{
using (var db = new NorthwindContext())
{
...
}
}
... within your data access method. Did you do the same thing in your GetById method? If so, did you remember to detach the object you got back so that it could be attached later in a different context?
public Category GetById(int categoryId)
{
using (var db = new NorthwindContext())
{
Category category = (from c in db.Category where Category.ID == categoryId select c).First();
db.Detach(category);
}
}
That way when you call Attach it isn't trying to step on an already-attached context. Does that help?
As you pointed out in your comment, this poses a problem when you're trying to modify an item and then tell your database layer to save it, because once an item is detached from its context, it no longer keeps track of the changes that were made to it. There are a few ways I can think of to get around this problem, none of them perfect.
If your architecture supports it, you could expand the scope of your context enough that your Save method could use the same context that your GetById method uses. This helps to avoid the whole attach/detach problem entirely, but it might push your data layer a little closer to your business logic than you would like.
You can load a new instance of the item out of the new context based on its ID, set all of its properties based on the category that is passed in, and then save it. This costs two database round-trips for what should really only need one, and it isn't very maintainable.
You can dig into the context itself to mark the Category's properties as changed.
For example:
public void Save(Category category)
{
using (var db = new NorthwindContext())
{
db.Attach(category);
var stateEntry = db.ObjectStateManager.GetObjectStateEntry(category);
foreach (var propertyName in stateEntry.CurrentValues.DataRecordInfo.FieldMetadata.Select(fm => fm.FieldType.Name)) {
stateEntry.SetModifiedProperty(propertyName);
}
db.SaveChanges();
}
}
This looks a little uglier, but should be more performant and maintainable overall. Plus, if you want, you could make it generic enough to throw into an extension method somewhere so you don't have to see or repeat the ugly code, but you still get the functionality out of it.