总是报nullpointException解决方案

总是报nullpointException
2013-11-28 19:16:54 org.apache.struts2.dispatcher.Dispatcher error
严重: Exception occurred during processing request: null
java.lang.NullPointerException
at com.sun.proxy.$Proxy6.findUser(Unknown Source)
at com.lovo.action.UserAction.login(UserAction.java:58)


我把对象都输出来了  都不是null  但是还是要报nullpointException
[解决办法]

     
    public String login() throws Exception{
//        ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
        String str  = "lose";
        us = (UserService)ac.getBean("usi");
        System.out.println("us="+us);
        System.out.println("user="+user);
        int i = us.findUser(user);
        if(i>0){
            ServletActionContext.getRequest().getSession().setAttribute("user", user);
            str = "loginSuccess";
        }
        return str;
    }