大家帮我看看 这是怎么回事？

Question

HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception javax.servlet.ServletException: java.lang.NullPointerException
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:515)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:419)
root cause java.lang.NullPointerException
com.csu.dao.UsersDaoImpl.findLogin(UsersDaoImpl.java:97)
com.csu.service.LoginService.isLogin(LoginService.java:22)
com.csu.action.LoginAction.execute(LoginAction.java:46)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:404)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:267)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:229)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:221)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:86)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)
com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)
com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:150)
org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:48)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:86)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)
com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:123)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)
com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:167)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:86)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)
com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)
com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:105)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)
com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)
com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept

Answer 1

com.csu.dao.UsersDaoImpl.findLogin(UsersDaoImpl.java:97)
UsersDaoImpl类的findLogin方法报空

Answer 2

java.lang.NullPointerException
 com.csu.dao.UsersDaoImpl.findLogin(UsersDaoImpl.java:97)
 com.csu.service.LoginService.isLogin(LoginService.java:22)
 com.csu.action.LoginAction.execute(LoginAction.java:46)
 空指针异常，找到上面的类，对应的行的代码。

Answer 3

package com.csu.dao;import java.util.Iterator;
import java.util.List;import org.hibernate.Query;
import org.hibernate.Session;
import org.springframework.orm.hibernate3.HibernateTemplate;
import org.springframework.orm.hibernate3.support.HibernateDaoSupport;import com.csu.po.Users;
import com.csu.util.*;public class UsersDaoImpl extends  HibernateDaoSupport implements UsersDao { public void delete(Long id) {
/*Session session=HibernateUtil.getSession();
session.beginTransaction();
//使用HQL查询
String hql="DELETE Users WHERE id=?";
Query q = session.createQuery(hql);
q.setLong(0, id);
q.executeUpdate();

//事务提交
session.getTransaction().commit();
//关闭session
HibernateUtil.closeSession(session);
        */
this.getHibernateTemplate().delete(this.getHibernateTemplate().get(Users.class, id));
} public List queryAll() {
/*Session session=HibernateUtil.getSession();
String hql="FROM Users as users ";
Query q=session.createQuery(hql);
List list = q.list();
Users user = (Users) list.get(0);
System.out.println(user.getName());
HibernateUtil.closeSession(session);
return list;
*/
return this.getHibernateTemplate().find("from Users");
} public Users queryById(Long id) {
/*
 * 
 Session session=HibernateUtil.getSession();
String hql="FROM Users as users WHERE users.id=?";
Query q=session.createQuery(hql);
q.setLong(0, id);
List list=q.list();
Users u=null;
//遍历是否存在该id的产品，如果存在就进行输出
Iterator  iter=list.iterator();
if(iter.hasNext()){
u=(Users) iter.next();
}

HibernateUtil.closeSession(session);
return u;
*/
return (Users)this.getHibernateTemplate().get(Users.class, id);

}
    
//添加用户
public void save(Users u) {
//创建Session
//Session session = HibernateUtil.getSession();

//开启事物
//session.beginTransaction();
//保存数据
//session.save(u);
//事务提交
//session.getTransaction().commit();
//关闭session
//HibernateUtil.closeSession(session);
this.getHibernateTemplate().save(u);
} public void update(Users u) {
/*
 Session session = HibernateUtil.getSession();
session.beginTransaction();
session.update(u);
session.getTransaction().commit();
HibernateUtil.closeSession(session);
*/
this.getHibernateTemplate().saveOrUpdate(u);
} public boolean findLogin(Users u) {
// TODO Auto-generated method stub
String hql="from Users where name='"+u.getName()+"'and password='"+u.getPassword()+"'";
System.out.println(hql);
List userlist=this.getHibernateTemplate().find(hql);
if(userlist.size()>0)  return true;
else 
return false;
} }

Answer 4

if(userlist.size()>0) return true;
如果没有找到用户，userlist = null;这句就会报空

Answer 5

看了你的代码，应该是Users对象的name或者password为空，所以报错，如下：
String hql="from Users where name='"+u.getName()+"'and password='"+u.getPassword()+"'";
上边代码在使用 u.getName() 进行字符连接操作时，要确保u.getName()不等于null。
具体做法是，使用之前进行为空判断if（null!=u.getName()）{...}

Answer 6

把 userlist.size() 换成 userlist.isEmpty(),同时确保参数穿过来正常