jsp出现java.lang.NullPointerException 异常

[cmxhuman]

public ActionForward doSelectteacher(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) {
Map map = new HashMap();
try {
int teacherId = Integer.parseInt(request.getParameter("id"));//这里id可以取到
System.out.print("teacherId="+teacherId);
String sql="from Teacher where teacherId = "+teacherId+"";
System.out.println(sql);
List<Teacher> teachers = teacherDAO.findByHQL(sql);单步调试只能到这里，再往下就直接报异常java.lang.NullPointerException
Teacher teacher = teachers.get(0);
if(teacher != null) {
int courseId = teacher.getCourseId();
DetachedCriteria dc = org.hibernate.criterion.DetachedCriteria.forClass(Teacher.class);
dc.createAlias("coursse", "cou");
dc.add(Restrictions.eq("cou.courseId", courseId));
Page.util( request, achievementService,dc,"dataList","param=doSelect",map,Page.PAGESIZE);//分页
}
return mapping.findForward("show");
} catch (Exception e) {
request.setAttribute("exceptions",e);
return mapping.findForward("exceptions");
}
}

hibernate配置都是正常的，可以正常连接，有teacher和course表，teacher通过courseId和course关联，DEBUG调试可以运行到以上红色，再往下就直接捕获异常显示了

[海会圣贤]

teacherDAO为空啊，你没有set进去吧。

看看你的配置文件吧。

[qiheia]

确定下teacherDAO这个对象是否为空

[cmxhuman]

设置了。。

public class AchievementAction extends DispatchAction {

private ITeacherDAO teacherDAO;

public void setTeacherDAO(ITeacherDAO teacherDAO) {
this.teacherDAO = teacherDAO;
..... }

[gulang76]

teacherDAO的代码也贴出来看看

[Mybeautiful]

[Quote=引用 3 楼 cmxhuman 的回复:]
设置了。。

public class AchievementAction extends DispatchAction {

private ITeacherDAO teacherDAO;

public void setTeacherDAO(ITeacherDAO teacherDAO) {
this.teacherDAO = teacherDAO;
..... }
[/Quote]

在这个set方法设断点，我可以确定程序不会进这里。 spring没有正确的注入。

[cmxhuman]

果然是teacherDAO没有注入，问题解决了，这个注入的我当时忘了，各位谢谢了

[cmxhuman]

package com.dao;

import com.po.Teacher;

/**
* TeacherDAO
* @author JSmart Tools
*/
public class TeacherDAO extends GenericHibernateDAO<Teacher, Integer> implements ITeacherDAO {

}


package com.dao;

import com.po.Teacher;

/**
* TeacherDAO
* @author JSmart Tools
*/
public interface ITeacherDAO extends GenericDAO<Teacher,Integer> {

}


package com.dao;

import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.LockMode;
import org.hibernate.criterion.DetachedCriteria;

/**
* @author JSmart Tools
*/
public interface GenericDAO<T extends Serializable, PK extends Serializable> {
......
public abstract List findByHQL(String queryString);
......
}


package com.dao;

import java.io.Serializable;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.SQLException;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;

import org.apache.commons.beanutils.PropertyUtils;
import org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.LockMode;
import org.hibernate.SQLQuery;
import org.hibernate.Session;
import org.hibernate.criterion.DetachedCriteria;
import org.hibernate.criterion.Example;
import org.hibernate.criterion.MatchMode;
import org.hibernate.criterion.Order;
import org.hibernate.criterion.Projections;
import org.hibernate.criterion.Restrictions;
import org.springframework.orm.hibernate3.HibernateCallback;
import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

/**
* GenericHibernateDao 继承 HibernateDao，简单封装 HibernateTemplate 各项功能，
* 简化基于Hibernate Dao 的编写。
* @author JSmart Tools
*/
@SuppressWarnings("unchecked")
public class GenericHibernateDAO<T extends Serializable, PK extends Serializable> extends HibernateDaoSupport implements GenericDAO<T, PK>
{
// 实体类类型(由构造方法自动赋值)
private Class<T> entityClass;

// 构造方法，根据实例类自动获取实体类类型
public GenericHibernateDAO() {
this.entityClass = null;
Class c = getClass();
Type t = c.getGenericSuperclass();
if (t instanceof ParameterizedType) {
Type[] p = ((ParameterizedType) t).getActualTypeArguments();
this.entityClass = (Class<T>) p[0];
}
}
.......

public List<T> findByHQL(final int currPage, final int pagesize,
final String hql) {
List list = this.getHibernateTemplate().executeFind(
new HibernateCallback() {
public Object doInHibernate(Session session)
throws HibernateException, SQLException {
List result = session.createQuery(hql).setFirstResult(
currPage > 1 ? (currPage - 1) * pagesize : 0)
.setMaxResults(pagesize).list();
return result;
}
});
return list;
}
.....
}

[dbx915]

teacherDAO为空，应该是配置文件的问题吧，检查一下在Spring注入时是不是不对，是不是名字写的不对应

[bossdai]

应该是你的dao注入失败了 要么就是你的查询sql数据库连接错误

[muler1988]

恩？？ 我晕 那个findByHQL明明是传了3个三个参数吗

[muler1988]

Sorry 我看错了

[Java技术栈]

teacherDAO这个接口没有在spring中注入 或是没有set方法 LZ试试看吧

[Joy]

teacherDAO 加个静态修饰符

[wymaweiyue]

可能是Spring注入的时候配置文件中那里写错了，说不定就是大小写的问题，仔细看看。

[kuailexiaobuding4]

哈哈看看的daoimpl方法测试写个main方法测试下。

[rainsilence]

断点打在this.teacherDAO = teacherDAO;这句上
看看有没有进来

[空心兜兜]

肯定是什么值没有得到