假设已经在session中存入了名为"currentUser"的User对象，则取出该数据的正确语句是（ ）
User user = session.getAttribute("currentUser");
User user = (User)session.getAttribute("currentUser");
Object user = session.getAttribute("currentUser");
String user = (String)session.getAttribute("currentUser");
session取对象要用getAttribute方法，取出的对象是Object类型
