nullpointer 谁帮我看看原因在哪里
用JSF+Hibernate+Spring编写一个新闻发布系统，结果在登录过程那一步就卡住了，在前台输入用户名密码后出现以下错误信息：
严重: java.lang.NullPointerException
javax.faces.el.EvaluationException: java.lang.NullPointerException
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:97)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:91)
at javax.faces.component.UICommand.broadcast(UICommand.java:383)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:447)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:752)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:97)
at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:251)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:117)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:244)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at cr.kiwan.bean.Login.validate(Login.java:23)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.el.parser.AstValue.invoke(AstValue.java:191)
at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:276)
at com.sun.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:68)
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:77)
... 20 more
2012-5-26 3:01:08 com.sun.faces.lifecycle.InvokeApplicationPhase execute
警告: #{login.validate}: java.lang.NullPointerException
javax.faces.FacesException: #{login.validate}: java.lang.NullPointerException
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:107)
at javax.faces.component.UICommand.broadcast(UICommand.java:383)
at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:447)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:752)
at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:97)
at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:251)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:117)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:244)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Unknown Source)
Caused by: javax.faces.el.EvaluationException: java.lang.NullPointerException
at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:97)
at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:91)
... 19 more

我的login.java部分代码如下：
public class Login {
private String name;
private String pass;
private String nerror = "";
private String perror = "";
public static final String USER = "user";
private AdminDAO adminDao;
public String validate(){
String forward = "failure";
System.out.print("username="+name+";password="+pass);
List<Admin> checkedUser = adminDao.findByUsername(name);try{
if(checkedUser.isEmpty()||checkedUser.get(0).getUserpass()!=pass)
{
if(adminDao.findByUsername(name).isEmpty())
{
nerror = "用户名错误";
}
else{
perror = "密码错误";
}
}
else{
FacesContext fxt = FacesContext.getCurrentInstance();
Map session = fxt.getExternalContext().getSessionMap();
session.put(USER, checkedUser);
forward = "success";
}

提示空指针异常出在红色那一行
findbyusername（）方法如下：
public List<Admin> findByUsername(Object username)
{
try {
String queryString = "from Admin where username="
+"'"+username+"'";
return getHibernateTemplate().find(queryString);
} catch (RuntimeException re) {
log.error("find username failed", re);
throw re;
}

不知道为什么出现空指针异常，哪位大神给小弟指点下，做不下去了，非常急

}


[解决办法]
adminDao 是null,spring中，没有正确设置值
[解决办法]
private AdminDAO adminDao;
dao申明后没有实例化所以为null；
如果用的是spring的javabean管理的话需要给dao加上注解！
[解决办法]
你要把dao的值注入进去，才不会为空。
[解决办法]

Java code

@Autowiredprivate AdminDAO adminDao;