无法捕获onFailure() GWT AsyncCallback

Question

我正在创建一个需要用户身份验证的appliaction。当我试图登录时，我有一个问题。当我键入正确的用户名和密码时，将调用onSuccess方法。但是，当我键入错误的字段或空字段时，就不会调用onFailure()方法。

我真的很想知道为什么会这样。因为我不想在用户名或密码不正确时显示某种对话框。

这是ClickHandler，它从字段中获取用户名和密码：

loginButton.addClickHandler(new ClickHandler() {

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

这是执行用户约束的方法，正如我所说，如果我有正确的用户名/密码，它就能工作。它显示我的警告消息，但如果不正确，则不显示任何警告消息。

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();
        }
    });
}

更新服务器部件。

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;
}

}

提前感谢

Answer 1

只有当您在服务器上抛出异常时，才会调用onFailure方法。现在，如果没有找到用户，您只需返回一个空对象。