jsp获取实体属性报错的问题 ?报错

报错为空指针，应该是没获取到值，但是我不知道具体哪里出了问题..
代码如下：
User实体
public class User{
private String username;
private String password;
//setter和getter
public User() {
}
public User(String username,String password){
this.username = username;
this.password = password;
}
}
登录Action
public class LoginAction extends ActionSupport
{
private User user;

public void setUser(User user){
    this.user = user;
}
public User getUser(User user){
    return this.user;
}
public String execute() throws Exception
{
    if (user.getUsername().equals("user") && user.getPassword().equals("123"))
    {
        return SUCCESS;
    }
    return ERROR;
}

}
登录jsp

 <s:form action="login">
    <s:textfield name="user.username" key="user"/>
    <s:textfield name="user.password" key="pass"/>
    <s:submit key="login"/>
</s:form>

能不能指教一下具体问题在哪里，卡着好几天了，看书调试一直是空指针错误