Spring 3.2和Hibernate 4 - 由于SessionFactory为null而导致NullPointerException异常

Question

我试图将我的非常小的应用程序转换为Spring 3.2和Hibernate 4，但我无法使它与会话正常运行。本段下面的一些信息，但最终sessionFactory每次到达DAO时总是为空，我无法弄清楚原因。

比较控制台到Hibernate 3，在启动休眠3只显示了这个：
2012年11月23日下午10时51分52秒org.springframework.orm.hibernate3.LocalSessionFactoryBean buildSessionFactory INFO：构建新的SessionFactory

堆栈跟踪：
显示java.lang.NullPointerException dao.CSSDAOImpl.selectAllCSS（CSSDAOImpl.java:21）

休眠-CF g.xml

<?xml version="1.0" encoding="UTF-8"?> 


<beans xmlns="http://www.springframework.org/schema/beans" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx" 
    xsi:schemaLocation=" 
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd 
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd"> 

    <bean id="myDataSource" 
     class="org.springframework.jdbc.datasource.DriverManagerDataSource"> 
     <property name="driverClassName" value="org.apache.derby.jdbc.EmbeddedDriver"></property> 
     <property name="url" value="jdbc:derby:C:\Users\Steven\MyDB"></property> 
    </bean> 

    <bean id="sessionFactory" 
     class="org.springframework.orm.hibernate4.LocalSessionFactoryBean"> 
     <property name="packagesToScan" value="net.form" /> 
     <property name="dataSource" ref="myDataSource"></property> 
     <property name="hibernateProperties"> 
      <props> 
       <prop key="hibernate.dialect">org.hibernate.dialect.DerbyTenSevenDialect 
       </prop> 
       <prop key="hibernate.show_sql">true</prop> 
      </props> 
     </property> 
     <property name="annotatedClasses"> 
      <list> 
       <value>net.form.StyleChooser</value> 
      </list> 
     </property> 
    </bean> 

    <bean id="transactionManager" 
     class="org.springframework.orm.hibernate4.HibernateTransactionManager"> 
     <property name="sessionFactory" ref="sessionFactory" /> 
    </bean> 

    <tx:annotation-driven transaction-manager="transactionManager" /> 

    <bean id="CSSDAO" class="dao.CSSDAOImpl"> 
     <property name="sessionFactory" ref="sessionFactory" /> 
    </bean> 

</beans> 

DAO：

package dao; 

import java.util.List; 

import org.hibernate.Session; 
import org.hibernate.SessionFactory; 
import org.hibernate.Transaction; 
import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.transaction.annotation.Transactional; 

import net.form.StyleChooser; 

public class CSSDAOImpl implements CSSDAO { 

    private SessionFactory sessionFactory; 

    @Autowired 
    public void setSessionFactory(SessionFactory sessionFactory) { 
     this.sessionFactory = sessionFactory; 
    } 

    @Transactional 
    public List selectAllCSS() { 
     Session session = sessionFactory.openSession(); 
     Transaction tx = session.beginTransaction(); 
     List l = session.createCriteria(StyleChooser.class).list(); 
     session.flush(); 
     tx.commit(); 
     return l; 
    } 

    @Transactional 
    public StyleChooser selectCSSById(Integer ID) { 
     Session session = sessionFactory.openSession(); 
     Transaction tx = session.beginTransaction(); 
     StyleChooser sc = (StyleChooser) session.get(StyleChooser.class, ID); 
     session.flush(); 
     tx.commit();   
     return sc; 
    } 

    @Transactional 
    public Integer insertCSS(StyleChooser insertCSS) { 
     Session session = sessionFactory.openSession(); 
     Transaction tx = session.beginTransaction(); 
     Integer id = (Integer) session.save(insertCSS); 
     session.flush(); 
     tx.commit(); 
     return id; 
    } 

    @Transactional 
    public void deleteCSS(Integer CSSId) { 
     Session session = sessionFactory.openSession(); 
     Transaction tx = session.beginTransaction(); 
     StyleChooser sc = (StyleChooser) session.get(StyleChooser.class, CSSId); 
     session.delete(sc); 
     session.flush(); 
     tx.commit(); 
    } 

    @Transactional 
    public void updateCSS(StyleChooser cssWithNewValues) { 
     Session session = sessionFactory.openSession(); 
     Transaction tx = session.beginTransaction(); 
     session.update(cssWithNewValues); 
     session.flush(); 
     tx.commit();   
    } 
} 

访问DAO ...

package net.controllers; 

import java.util.List; 
import javax.servlet.http.HttpServletRequest; 
import net.form.StyleChooser; 
import org.springframework.beans.factory.BeanFactory; 
import org.springframework.beans.factory.xml.XmlBeanFactory; 
import org.springframework.core.io.FileSystemResource; 
import org.springframework.core.io.Resource; 
import org.springframework.stereotype.Controller; 
import org.springframework.web.bind.annotation.RequestMapping; 
import org.springframework.web.bind.annotation.RequestMethod; 
import org.springframework.web.servlet.ModelAndView; 
import org.springframework.web.servlet.mvc.multiaction.MultiActionController; 
import dao.CSSDAOImpl; 

@Controller 
@RequestMapping("/stylechoosertable.html") 
public class IndexController extends MultiActionController { 

    Resource resource = new FileSystemResource(
      "C:/Users/Steven/Desktop/Programming/workspace/CSSGeneratorHibernate4/WebContent/WEB-INF/hibernate.cfg.xml"); 
    BeanFactory beanFactory = new XmlBeanFactory(resource); 
    CSSDAOImpl dao = (CSSDAOImpl) beanFactory.getBean("CSSDAO"); 

    @RequestMapping(method = RequestMethod.GET) 
    public ModelAndView showIndex(HttpServletRequest request) throws Exception { 
     List<StyleChooser> styleChooser = dao.selectAllCSS(); 
     return new ModelAndView("stylechoosertable", "styleChooser", styleChooser); 
    } 
} 

Answer 1

在Spring配置文件中进行以下更改：

<bean id="CSSDAO" class="dao.CSSDAOImpl"> 
    <property name="sessionFactory" ref="sessionFactory" /> 
</bean> 

现在，CSSDAOImpl删除所有静态修饰符：

private SessionFactory sessionFactory; 

public void setSessionFactory(SessionFactory sessionFactory) { 
    this.sessionFactory = sessionFactory; 
} 

这应该可以解决NPE！

Answer 2

为了保持干净利落，您应该在所有方法中使用@Transactional-Annotation，而不是手动打开会话，但始终使用sessionFactory.getCurrentSession（）。 ...

我想你会这样做，因为你使用tx：annotation-driven并且已经导入了注释。

除了Muel的回答，您还可以在setSessionFactory（）方法上使用@ Autowired-Annotation。