对于Java类，我假设您是指Servlet类，因为在任意Java类中设置会话属性没有意义。您可以在servlet的doGet /
doPost方法中执行类似的操作

public void doGet(HttpServletRequest request, HttpServletResponse response) {

    HttpSession session = request.getSession();
    String username = (String)request.getAttribute("un");
    session.setAttribute("UserName", username);
}