GWT retrieve list from datastore via serviceimpl - user-interface

Question

Hi I'm trying to retrieve a linkedhashset from the Google datastore but nothing seems to happen. I want to display the results in a Grid using GWT on a page. I have put system.out.println() in all the classes to see where I go wrong but it only shows one and I don't recieve any errors. I use 6 classes 2 in the server package(ContactDAOJdo/ContactServiceImpl) and 4 in the client package(ContactService/ContactServiceAsync/ContactListDelegate/ContactListGui). I hope someone can explain why this isn't worken and point me in the right direction.
public class ContactDAOJdo implements ContactDAO {
#SuppressWarnings("unchecked")
#Override
public LinkedHashSet<Contact> listContacts() {
PersistenceManager pm = PmfSingleton.get().getPersistenceManager();
String query = "select from " + Contact.class.getName();
System.out.print("ContactDAOJdo: ");
return (LinkedHashSet<Contact>) pm.newQuery(query).execute();
}
}
public class ContactServiceImpl extends RemoteServiceServlet implements ContactService{
private static final long serialVersionUID = 1L;
private ContactDAO contactDAO = new ContactDAOJdo() {
#Override
public LinkedHashSet<Contact> listContacts() {
LinkedHashSet<Contact> contacts = contactDAO.listContacts();
System.out.println("service imp "+contacts);
return contacts;
}
}
#RemoteServiceRelativePath("contact")
public interface ContactService extends RemoteService {
LinkedHashSet<Contact> listContacts();
}
public interface ContactServiceAsync {
void listContacts(AsyncCallback<LinkedHashSet <Contact>> callback);
}
public class ListContactDelegate {
private ContactServiceAsync contactService = GWT.create(ContactService.class);
ListContactGUI gui;
void listContacts(){
contactService.listContacts(new AsyncCallback<LinkedHashSet<Contact>> () {
public void onFailure(Throwable caught) {
gui.service_eventListContactenFailed(caught);
System.out.println("delegate "+caught);
}
public void onSuccess(LinkedHashSet<Contact> result) {
gui.service_eventListRetrievedFromService(result);
System.out.println("delegate "+result);
}
});
}
}
public class ListContactGUI {
protected Grid contactlijst;
protected ListContactDelegate listContactService;
private Label status;
public void init() {
status = new Label();
contactlijst = new Grid();
contactlijst.setVisible(false);
status.setText("Contact list is being retrieved");
placeWidgets();
}
public void service_eventListRetrievedFromService(LinkedHashSet<Contact> result){
System.out.println("1 service eventListRetreivedFromService "+result);
status.setText("Retrieved contactlist list");
contactlijst.setVisible(true);
this.contactlijst.clear();
this.contactlijst.resizeRows(1 + result.size());
int row = 1;
this.contactlijst.setWidget(0, 0, new Label ("Voornaam"));
this.contactlijst.setWidget(0, 1, new Label ("Achternaam"));
for(Contact contact: result) {
this.contactlijst.setWidget(row, 0, new Label (contact.getVoornaam()));
this.contactlijst.setWidget(row, 1, new Label (contact.getVoornaam()));
row++;
System.out.println("voornaam: "+contact.getVoornaam());
}
System.out.println("2 service eventListRetreivedFromService "+result);
}
public void placeWidgets() {
System.out.println("placewidget inside listcontactgui" + contactlijst);
RootPanel.get("status").add(status);
RootPanel.get("contactlijst").add(contactlijst);
}
public void service_eventListContactenFailed(Throwable caught) {
status.setText("Unable to retrieve contact list from database.");
}
}

Answer 1

It could be the query returns a lazy list. Which means not all values are in the list at the moment the list is send to the client. I used a trick to just call size() on the list (not sure how I got to that solution, but seems to work):
public LinkedHashSet<Contact> listContacts() {
final PersistenceManager pm = PmfSingleton.get().getPersistenceManager();
try {
final LinkedHashSet<Contact> contacts =
(LinkedHashSet<Contact>) pm.newQuery(Contact.class).execute();
contacts.size(); // this triggers to get all values.
return contacts;
} finally {
pm.close();
}
}
But I'm not sure if this is the best practice...