起因: org.o7planning.impl.EmployeDAOImpl.<init>(EmployeDAOImpl.java:34)的java.lang.NullPointerException

Question

这是我尝试实例化bean的file.XML : applicationDaoContext.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"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans-4.1.xsd">

 <bean id="EmployeDAO" class="org.o7planning.impl.EmployeDAOImpl">
     <property name="sessionFactory" ref="SessionFactory" />
 </bean>
</beans>  `

这是我的类EmployeDaooImpl，实例化失败：( hibernate spring maven tomcat server ) with eclipse

package org.o7planning.impl;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.o7planning.dao.EmployeDao;
import org.o7planning.Entity.Employe;
import org.hibernate.Query;

import org.hibernate.cfg.Configuration;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.transaction.annotation.Transactional;

@Transactional
public class EmployeDAOImpl implements EmployeDao {

    public EmployeDAOImpl() {
        super();


    }

        public void init(){
            new EmployeDAOImpl();
            System.out.println(" mossab method initi de la classe employimpldao");
        }
    private SessionFactory sessionFactory;

    Session session = sessionFactory.getCurrentSession();

            // methode implementer par l'interface
            @SuppressWarnings("unchecked")
            public List<Employe> getAllEmploye() {

                Session session = this.sessionFactory.getCurrentSession();

                List<Employe> list = session.createQuery("from EMPLOYEES").getResultList()  ;
                session.close();
                return list;
}
                // method implementer par l'interface   
            public Integer getMaxEmployeByID() {
                Session session = this.sessionFactory.getCurrentSession();
                String sql = "Select max(E.EMPLOYEE_ID) from EMPLOYEES E ";
                Query query = session.createQuery(sql);
                Integer maxEmployId = (Integer) query.uniqueResult();
                  if (maxEmployId == null) {
                      return 0;
                  }

                  return maxEmployId;
            }

                // methode implementer par l'interface
            public void createEmploy(String nom, String prenom) {

          Integer employId = getMaxEmployeByID() + 1;
          Employe employ = new Employe();
          employ.setId_Employe(employId);
          employ.setNom(nom);
          employ.setPrenom(prenom);
          Session session = this.sessionFactory.getCurrentSession();
          session.persist(employ);

    }

            public SessionFactory getSessionFactory() {
                return sessionFactory;
            }

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

}

Answer 1

您需要更改代码，如下所示：

private SessionFactory sessionFactory;
// Remove this line:
// Session session = sessionFactory.getCurrentSession();

此时，sessionFactory没有被赋值，所以它是null。当Spring向其注入值时，它的值不为空。Spring将调用setSessionFactory方法向Spring字段注入值。

你可以用setSessionFactory方法写更多的代码。