Exception while running GWT application

Question

I have built my first GWT app. giving no compilation errors neither run-time errors. However, when the application is loaded into the browser (using Interner Explorer) and I enter username and password field to validate the user, it throws exceptions. Using GWT-RPC method, entire code and interfaces are provided. I'm using HSQL for database connection(back end).

------------------CODE (CLIENT)

package com.vin.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.PasswordTextBox;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.TextBox;

public class HelloWorld implements EntryPoint{
    private UserServiceAsync UserService = (UserServiceAsync) GWT.create(UserService.class);
    public void onModuleLoad() {
        Button click=new Button("Click Here");
        Label name=new Label("Enter Name");
        Label passwrd=new Label("Enter Password");
        final TextBox t_name=new TextBox();
        final PasswordTextBox t_passwrd=new PasswordTextBox();
        click.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent ev) {
            String temp_user=t_name.getText();
            String temp_pass=t_passwrd.getText();
                 UserService.loginuser(temp_user, temp_pass, new AsyncCallback<String>() {
                     public void onFailure(Throwable caught) {
                             Window.alert("Please enter valid details");
                      }
                     public void onSuccess(String result) {
                         Window.alert("Welcome");
//                         Window.open("http://127.0.0.1:8888/ExWid.html?gwt.codesvr=127.0.0.1:9997", "Dem", null);
                     }
                 });
            }
        });
        RootPanel.get().add(name);
        RootPanel.get().add(t_name);
        RootPanel.get().add(passwrd);
        RootPanel.get().add(t_passwrd);
        RootPanel.get().add(click);
}
}

-----------------------------CLIENT INTERFACE (1)

package com.vin.client;

import com.google.gwt.user.client.rpc.RemoteService;

public interface UserService extends RemoteService {
    public String loginuser(String username, String password);
}

----------------------------CLIENT ASYNC INTERFACE

package com.vin.client;

import com.google.gwt.user.client.rpc.AsyncCallback;

public interface UserServiceAsync {
    public void loginuser(String username, String password, AsyncCallback<String> callback);
}

--------------------------IMPLEMENTATION OF CLIENT USERSERVICE (SERVER)...DATABASE CONNECTION

package com.vin.server;

import java.sql.DriverManager;
import java.sql.ResultSet;
import com.google.gwt.dev.generator.ast.Statement;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.server.rpc.RemoteServiceServlet;
import com.vin.client.UserService;

public class UserServiceImpl extends RemoteServiceServlet implements UserService{
    private static final long serialVersionUID = 1L;

    public String loginuser(String username,String password) {
        try {
            java.sql.Connection con = null;
            Class.forName("org.hsqldb.jdbcDriver");
            con = DriverManager.getConnection("jdbc:hsqldb:hsql://localhost/", "SA", "");
            Statement st=(Statement) con.createStatement();
            ResultSet rs=((java.sql.Statement) st).executeQuery("select username,password from lgfrm");
            String user=rs.getString(1);
            String pass=rs.getString(2);
            if(username.equals(user) && password.equals(pass)) {
                Window.alert("success");
            }
        }
    catch (Exception ae) {}
        return "success";
    }
}

------------------THE EXCEPTION LIST WHILE I'M TRYING TO VALIDATE A USER

15:22:54.583 [ERROR] [helloworld] Uncaught exception escaped com.google.gwt.event.shared.UmbrellaException: One or more exceptions caught, see full set in UmbrellaException#getCauses at com.google.gwt.event.shared.HandlerManager.fireEvent(HandlerManager.java:129) at com.google.gwt.user.client.ui.Widget.fireEvent(Widget.java:129) at com.google.gwt.event.dom.client.DomEvent.fireNativeEvent(DomEvent.java:116) at com.google.gwt.user.client.ui.Widget.onBrowserEvent(Widget.java:177) at com.google.gwt.user.client.DOM.dispatchEventImpl(DOM.java:1351)

And many more like these.

Answer 1

com.google.gwt.user.client.Window class provides access to the browser window's methods, properties, and events. So you can't use it in Serverside. Better you return String "success" when requirement meets, else return Exception, so that it is caught by onFailure on clientside.

Answer 2

I think you can't use Window.alert on server side (in UserServiceImpl class). There can be many clients and server can't know about what client it directed for.

But i'm not sure that it causes this error.