下面程序错误，麻烦帮忙看看怎么解决？还有什么需要的请各位大侠提出来

Question

严重: Servlet.service() for servlet default threw exceptionjava.lang.NullPointerExceptionat service.LoginAction.execute(LoginAction.java:43)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)at java.lang.reflect.Method.invoke(Method.java:597)at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:404)at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:267)at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:229)public class LoginAction extends ActionSupport{  private String username;  private String password;  private PersonDAO personManager;  /*其中的seter和geter方法省略了*/@Override  public String execute() throws Exception {  String flag = "";  Person per = new Person();  per.setUname(this.username);  per.setUpwd(this.password);  personManager.save(per);return flag;  } } save函数的的代码public class PersonDAO extends HibernateDaoSupport{public void save(Person transientInstance) {log.debug("saving Person instance");try {getHibernateTemplate().save(transientInstance);log.debug("save successful");} catch (RuntimeException re) {log.error("save failed", re);throw re;}}还有什么需要的请各位大侠提出来谢谢诶<bean id="PersonDAO" class="user.PersonDAO"><property name="sessionFactory"><ref bean="sessionFactory" /></property>

Answer 1

这个错误只能说明这个action在第43执行时出错了，具体什么错误应该贴出代码才能看的出
java.lang.NullPointerException，只能说明某个变量为空，如session 

你的PersonDAO 注主sessionFactory了吗，applicationContext有配置没有？

Answer 2

空指针的使用，这里很难看出问题，给全代码来看看