javafx的GUI的用户名列中不显示用户名

Question

当前，我有一个方法在场景加载后填充表，但是现在只有一列根本没有加载，这是另一张表的用户名列，我怀疑其中存在错误我的sql语句，但是我可能错了，并且该错误在其他地方。当前输出的结果在提供的https://imgur.com/iX8beaH

链接中

初始化方法

@FXML
    public void initialize()
    {
        try{
            searchStaff();
        } catch(SQLException ex)
        {
            System.out.println("Error occurred while getting employees information from DB.\n" + ex);
        }
        catch(ClassNotFoundException e)
        {
            System.out.println(e);
        }

        staffTableView.setOnMouseClicked((MouseEvent event) -> {
                    if (event.getClickCount() > 0) {
                        Staff staff = new Staff();
                        Users users = new Users();
                        staff = staffTableView.getSelectionModel().getSelectedItem(); // *** get selection from TableView ***
                        staffIDtxtfld.setText(staff.getStaffID());
                        fnametxtfld.setText(staff.getFname());
                        lnametxtfld.setText(staff.getLname());
                        fullNametxtfld.setText(staff.getFullName());
                        userRoleBox.setValue(staff.getRole());
                        taskPreftxtfld.setText(staff.getTaskPref());
                        usernametxtfld.setText(users.getUsername());


                    }
                });
    }

搜索人员

@FXML
    private void searchStaff() throws SQLException, ClassNotFoundException{
        try{
        staffIDColumn.setCellValueFactory(new PropertyValueFactory<>("staffID"));
        fnameColumn.setCellValueFactory(new PropertyValueFactory<>("fname"));
        lnameColumn.setCellValueFactory(new PropertyValueFactory<>("lname"));
        fullNameColumn.setCellValueFactory(new PropertyValueFactory<>("fullName"));
        taskPrefColumn.setCellValueFactory(new PropertyValueFactory<>("taskPref"));
        roleColumn.setCellValueFactory(new PropertyValueFactory<>("role"));
        userColumn.setCellValueFactory(new PropertyValueFactory<>("username"));

        ObservableList<Staff> staffData = EditUsersDAO.getStaffList();


        populateStaff(staffData);

        } catch (SQLException e){
            System.out.println("Error");     
        }
    }

填充StaffTable

@FXML
    private void populateStaff (ObservableList<Staff> staffData) throws ClassNotFoundException {

        staffTableView.setItems(staffData);
    }

EditUsers DAO

获取staffList

public static ObservableList<Staff> getStaffList() throws SQLException, ClassNotFoundException{
        Connection conn = DBConnection.getConnection();
        try
        {
        String sql = "SELECT * FROM Staff INNER JOIN Login ON Staff.staffID = Login.staff_ID";
        ResultSet rs = conn.createStatement().executeQuery(sql);
        ObservableList<Staff> staffList = setStaffList(rs);

        return staffList;
        } finally {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }


    }

设置人员列表

private static ObservableList<Staff> setStaffList(ResultSet rs) throws SQLException, ClassNotFoundException {

        ObservableList<Staff> staffList = FXCollections.observableArrayList();

        while (rs.next()){

        Staff staff = new Staff();
        Users users = new Users();


        users.setUsername(rs.getString("username"));

        staff.setStaffID(rs.getString("staffID"));
        staff.setFname(rs.getString("fname"));
        staff.setLname(rs.getString("lname"));
        staff.setRole(rs.getString("role"));
        staff.setTaskPref(rs.getString("task_Preference"));
        staff.setFullName(rs.getString("full_Name"));

        staffList.add(staff);
        }
        return staffList;
    }

更新： Users.java

public class Users {

    public SimpleStringProperty username;
    public SimpleStringProperty password;
    public SimpleStringProperty role;
    public SimpleStringProperty staff_ID;

    public Users(){

        this.staff_ID = new SimpleStringProperty();
        this.password = new SimpleStringProperty();
        this.username = new SimpleStringProperty();
        this.role = new SimpleStringProperty();
    }

     public StringProperty staffIDProperty(){
        return staff_ID;
        } 

     public StringProperty usernameProperty(){
        return username;
        } 

     public StringProperty passwordProperty(){
        return password;
        } 

     public StringProperty roleProperty(){
        return role;
        }


      /**
     * @return the staff_ID
     */
    public String getStaffID() {
        return staff_ID.get();
    }

    /**
     * @param staffID the staff_ID to set
     */
    public void setStaffID(String staffID) {
        this.staff_ID.set(staffID);
    }

     /**
     * @return the username
     */
    public String getUsername() {
        return username.get();
    }

    /**
     * @param username the username to set
     */
    public void setUsername(String username) {
        this.username.set(username);
    }
     /**
     * @return the password
     */
    public String getPassword() {
        return password.get();
    }

    /**
     * @param password the password to set
     */
    public void setPassword(String password) {
        this.password.set(password);
    }
     /**
     * @return the role
     */
    public String getRole() {
        return role.get();
    }

    /**
     * @param role the role to set
     */
    public void setRole(String role) {
        this.role.set(role);
    }
}