GWT通过serviceimpl从数据存储区检索列表 [英] GWT retrieve list from datastore via serviceimpl

问题描述

我正在尝试从Google数据存储区检索一个linkedhashset，但似乎没有发生。我想在页面上使用GWT在Grid中显示结果。我已经把system.out.println（）放在所有的类中，看看我出错了，但它只显示一个，我没有收到任何错误。我在服务器包（ContactDAOJdo / ContactServiceImpl）中使用6个类2，在客户端包中使用4个类（ContactService / ContactServiceAsync / ContactListDelegate / ContactListGui）。我希望有人可以解释为什么这不是工作，并指出我正确的方向。

  public class ContactDAOJdo实现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实现ContactService {
 private static final long serialVersionUID = 1L; 
 private ContactDO contactDAO = new ContactDAOJdo（）{
 @Override 
 public LinkedHashSet< Contact> listContacts（）{
 LinkedHashSet< Contact> contacts = contactDAO.listContacts（）; 
 System.out.println（service imp+ contacts）; 
返回联系人; 
} 
} 
 
 @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 catch）{
 gui.service_eventListContactenFailed ）; 
 System.out.println（delegate+ catch）; 
} 
 public void onSuccess（LinkedHashSet< Contact> result）{
 gui.service_eventListRetrievedFromService（result）; 
 System.out.println（delegate+ result）; 
} 
}）; 
} 
} 
 
 public class ListContactGUI {
 protected Grid contactlijst; 
 protected ListContactDelegate listContactService; 
私人标签状态; 
 
 public void init（）{
 status = new Label（）; 
 contactlijst = new Grid（）; 
 contactlijst.setVisible（false）; 
 status.setText（正在检索联系人列表）; 
 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 catch）{
 status.setText（无法从数据库中检索联系人列表）; 
} 
} 
  

解决方案

可以查询返回一个懒惰列表。这意味着在列表发送给客户端时，并不是所有的值都在列表中。我使用一个技巧，只需调用列表中的 size（）（不知道我如何得到该解决方案，但似乎有效）：

  public LinkedHashSet< Contact> listContacts（）{
 final PersistenceManager pm = PmfSingleton.get（）。getPersistenceManager（）; 
 try {
 final LinkedHashSet< Contact> contacts = 
（LinkedHashSet< Contact>）pm.newQuery（Contact.class）.execute（）; 
 contacts.size（）; //这将触发获取所有值。 
返回联系人; 
} finally {
 pm.close（）; 
} 
  

}

但我不知道这是否是最佳做法...

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.");
}
}

解决方案

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...

这篇关于GWT通过serviceimpl从数据存储区检索列表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！