Unable to catch onFailure() GWT AsyncCallback

Question

I am creating an appliaction which requires user authentication. I have one problem when I'm trying to log in. When I type a correct username and password, the onSuccess method is called. But when I type a wrong one, or empty fields, then the onFailure() method is NOT called.

I really want to know why this is happening. Because I wan't to display some sort of dialogbox when the username or password is incorrect.

This is the ClickHandler, which takes the username and password from the fields:

loginButton.addClickHandler(new ClickHandler() {

        @Override
        public void onClick(ClickEvent event) {
            String username = usernameBox.getText();
            String password = passwordBox.getText();
            performUserConnection(username, password);
        }
    });

And this is the method that performs the user conenction, which as I said, works if I have a correct username/ password. It displays my alert message, but it does not display any alert message if it's not correct.

private static void performUserConnection(String username, String password) {
    DBConnectionAsync rpcService = (DBConnectionAsync) GWT.create(DBConnection.class);
    ServiceDefTarget target = (ServiceDefTarget) rpcService;
    String moduleRelativeURL = GWT.getModuleBaseURL() + "DBConnectionImpl";
    target.setServiceEntryPoint(moduleRelativeURL);

    rpcService.authenticateUser(username, password, new AsyncCallback<User>() {

        @Override
        public void onSuccess(User user) {
            Window.alert("TRALALA. Username: " + user.getUsername());
        }

        @Override
        public void onFailure(Throwable caught) {
            Window.alert("LALALALAL");
            // DialogBox dialogBox = createDialogBox();
            // dialogBox.setGlassEnabled(true);
            // dialogBox.setAnimationEnabled(true);
            // dialogBox.center();
            // dialogBox.show();
        }
    });
}

UPDATE Server Part.

public class DBConnectionImpl extends RemoteServiceServlet implements DBConnection {

private static final long serialVersionUID = 1L;

private String URL = new String("jdbc:mysql://localhost:3306");
private String user = "root";
private String pass = "andrei";
private String schema = "administrare_bloc";

public DBConnectionImpl() {
}

private Connection getConnection() throws Exception {
    Properties props = new Properties();
    props.setProperty("user", user);
    props.setProperty("password", pass);
    props.setProperty("zeroDateTimeBehavior", "convertToNull");
    Class.forName("com.mysql.jdbc.Driver").newInstance();
    Connection conn = DriverManager.getConnection(URL + "/" + schema, props);

    return conn;
}

@Override
public User authenticateUser(String username, String password) throws Exception {

    User returnUser = null;
    Connection conn = null;
    PreparedStatement stmt = null;
    ResultSet rs = null;

    try {
        conn = getConnection();

        try {
            String q = "select * from users where username=? and password=?";
            stmt = conn.prepareStatement(q);
            stmt.setString(1, username);
            stmt.setString(2, password);
            rs = stmt.executeQuery();

            while (rs.next()) {
                int id = rs.getInt("id");
                String user = rs.getString("username");
                String pass = rs.getString("password");
                String type = rs.getString("type");

                returnUser = new User(id, user, pass, type);
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }

    } catch (SQLException ex) {
        ex.printStackTrace();
    } finally {
        rs.close();
        stmt.close();
        conn.close();
    }

    return returnUser;
}

}

Thanks in advance

Answer 1

The onFailure method will only be Called if you throw an exception on the server. Now you just return a null object if no user is found.